Techniques to Measure Surface Recombination Velocity in Solar Cells

A solar cell with reduced recombination losses at side edges, comprising a substrate, a doped conductive layer, a first passivation film layer, and a first dielectric layer. The first passivation film layer completely covers the side surfaces of the substrate, and a second passivation film layer is stacked on the surface of a passivated contact layer facing away from the substrate. The second passivation film layer is made of a material including at least one of SiNx, SiONx, and SiOx.

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Method for diagnosing internal loss mechanisms in solar cells by analyzing the type of simulated current density-voltage (JV) curve, enabling identification of specific loss mechanisms such as recombination, series resistance, and shunt resistance.

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A method for evaluating the recombination lifetime of a semiconductor sample with precision, comprising: measuring the sample using a photoconductivity decay method to obtain a decay curve; fitting the decay curve with a model expression including an exponential decay term and a constant term; and determining the recombination lifetime from the fitted expression. The method enables accurate measurement of recombination lifetime in semiconductor samples, particularly those with high cleanliness where surface recombination dominates.

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A method for evaluating semiconductor samples using photoconductive decay (PCD) measurements, comprising multiple measurements with varying surface charge densities, signal processing using a model equation with exponential and constant terms, and determination of recombination lifetime and surface recombination lifetime from the processed data. The method enables extraction of recombination lifetime and surface recombination lifetime from PCD measurements, and can be used for evaluating semiconductor wafers and determining manufacturing conditions.

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I V testing during production is a valuable tool not only for evaluating and sorting cells and modules based on their performance but also for identifying the underlying causes driving the performance. The amount of available information is increased by the high volume of measurements, revealing some information that would not be accessible with a measurement of only a few samples. To make full use of I V testing, a comprehensive measurement and analysis system is required that takes into consideration the characteristics of different device types. The goal of characterizing the electronic parameters of a solar cell at I V test requires more than the typical I sc , V oc , power, and FF measurement. In addition to these traditional figures of merit, the complete characterization of the solar cell requires measurement of the substrate doping, the series resistance, the lifetime and surface recombination parameters, and reverse breakdown characteristics. This chapter discusses several distinct methods for characterizing cells and modules at I V test, with a focus on making use o... Read More

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The study of the crystalline silicon solar cell (n+/p/p+) with vertical multi junction connected in series through the resolution of the diffusion equation (2D) in dynamic regime relative to the density of minority carriers in the (p) base, provided with the boundary conditions associated with the recombination velocity at the junction and on the rear side, leads to the electrical characteristics, current-voltage, power-voltage delivered and Fill factor.This work shows and analyzes on these quantities, the effects of the frequency of modulation of the incident polychromatic light, of the recombination velocity of the minority carriers on the back side and the junction, the thickness of the base and its depth of the solar cell.

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The effects of surface recombination on the steady-state carrier profiles and photocurrent in perovskite solar cells are investigated in this paper. The continuity equations for both holes and electrons are solved considering carrier drift and diffusion under the exponential carrier generation profile in the perovskite layer and considering both bulk and interface carrier recombination. An analytical expression for the solar-induced photocurrent is derived. The rate of carrier recombination at the interfaces has a very significant effect on the carrier profile, photocurrent, and, hence, on the charge collection efficiency. The external current density is calculated considering the dark current and nominal solar spectrum-induced photocurrent. The proposed model is fitted and verified with published experimental results from various publications. The fittings of the model with experimental results provide information about the interface and bulk charge carrier transport parameters.

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Abstract The SchockleyQuisser (SQ) limit of 28.64% is distant from the Sb 2 S 3 solar cells record power conversion efficiency ( PCE ), which is 8.00%. Such poor efficiency is mostly owing to substantial interface-induced recombination losses caused by defects at the interfaces and misaligned energy levels. The endeavor of this study is to investigate an efficient Sb 2 S 3 solar cell structure via accurate analytical modeling. The proposed model considers different recombination mechanisms such as non-radiative recombination, Sb 2 S 3 /CdS interface recombination, Auger, SRH, tunneling-enhanced recombination, and their combined impact on solar cell performance. This model is verified against experimental work (Glass/ITO/CdS/Sb 2 S 3 /Au) where a good coincidence is achieved. Several parameters effects such as thickness, doping, electronic affinity, and bandgap are scrutinized. The effect of both bulk traps located in CdS and Sb 2 S 3 on the electrical outputs of the solar cell is analyzed thoroughly. Besides, a deep insight into the effect of interfacial traps on solar cell figures... Read More

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Recombination of free charges is a key loss mechanism limiting the performance of organic semiconductor-based photovoltaics such as solar cells and photodetectors. The carrier density-dependence of the rate of recombination and the associated rate coefficients are often estimated using transient charge extraction (CE) experiments. These experiments, however, often neglect the effect of recombination during the transient extraction process. In this work, the validity of the CE experiment for low-mobility devices, such as organic semiconductor-based photovoltaics, is investigated using transient drift-diffusion simulations. We find that recombination leads to incomplete CE, resulting in carrier density-dependent recombination rate constants and overestimated recombination orders; an effect that depends on both the charge carrier mobilities and the resistancecapacitance time constant. To overcome this intrinsic limitation of the CE experiment, we present an analytical model that accounts for charge carrier recombination, validate it using numerical simulations, and employ it to correct... Read More

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The recombination rate in the space charge region (SCR) of a silicon-based barrier structure with a long ShockleyReedHall lifetime is calculated theoretically by taking into account the concentration gradient of excess electron-hole pairs in the base region. Effects of the SCR lifetime and applied voltage on the structure ideality factor have been analyzed. The ideality factor is significantly reduced by the concentration gradient of electron-hole pairs. This mechanism provides an increase of the effective lifetime compared to the case when it is insignificant, which is realized at sufficiently low pair concentrations. The theoretical results have been shown to be in agreement with experimental data. A method of finding the experimental recombination rate in SCR in highly efficient silicon solar cells (SCs) has been proposed and implemented. It has been shown that at the high excess carrier concentration exceeding 1015 cm3 the contribution to the SCR recombination velocity from the initial region of SCR that became neutral is significant. From a comparison of theory with experimen... Read More

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Impedance spectroscopy provides relevant knowledge on the recombination and extraction of photogenerated charge carriers in various types of photovoltaic devices. In particular, this method is of great benefit to the study of crystalline silicon (c-Si)-based solar cells, a market-dominating commercial technology, for example, in terms of the comparison of various types of c-Si devices. This study investigates the dark and light electrophysical characteristics of a heterojunction silicon solar cell fabricated using plasma-enhanced chemical vapor deposition. The measurements are performed at various applied biases, enabling the determination of complex resistance, characteristic time, capacitive response and impurity concentration within the semiconductor junction and to correlate them with the device performance. In addition, the impedance spectra of the studied cell were investigated as a function of temperature. Studies of the frequency and temperature dependences of capacitance do not reveal a significant presence of thermally activated centers of free carrier capture, concomitant ... Read More

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Determining exactly how the performance of a thin-film photovoltaic device is limited by a particular recombination mechanism can be difficult, particularly in the case of CdTe solar cells. As a result, efforts are being made to improve all parts of the device without good knowledge of which improvements are necessary. To understand where the device limitation is, the recombination current densities of at least one on of the interfaces must be known. Here, we present a method to determine which recombination mechanisms is limiting. First, back illuminated quantum efficiency measurements are used to determine the key parameters of the back interface the back surface recombination velocity and the band bending near the back surface. Once these back interface parameters are determined, the recombination current densities can be calculated for a front illuminated device to determine the limiting mechanism. The validity of the approach is tested using previously reported data.

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Abstract With the improvement of surface passivation, bulk recombination is becoming an indispensable and decisive factor to assess the theoretical limiting efficiency ( ) of crystalline silicon (cSi) solar cells. In simultaneous consideration of surface and bulk recombination, a modified model of evaluation is developed. Surface recombination is directly depicted with contact selectivity while bulk recombination is revised on the aspects of ideality factor and wafer thickness. The of the doubleside silicon heterojunction (SHJ) and doubleside tunnelingoxide passivating contact (TOPCon) solar cells are numerically simulated using the new model as 28.99% and 29.19%, respectively. However, the of singleside TOPCon solar cells, the more practicable scenario, is only 27.79%. Besides, the of the doubleside SHJ solar cells would exceed the doubleside TOPCon solar cells if the recombination parameter of the noncontacted area is higher than 0.6 fA/cm 2 , instead of perfect passivation. Our results are instructive in accurately assessing efficiency potential and accordingly optimizing ... Read More

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Knowledge regarding the temperature dependence of the surface recombination at the interface between silicon and various dielectrics is critically important as it 1) provides fundamental information regarding the interfaces and 2) improves the modeling of solar cell performance under actual operating conditions. Herein, the temperature and carrierdependent surface recombination at the siliconoxide/silicon and aluminumoxide/silicon interfaces in the temperature range of 2590 C using an advanced technique is investigated. This method enables to control the surface carrier population from heavy accumulation to heavy inversion via an external bias voltage, allowing for the decoupling of the bulk and surface contributions to the effective lifetime. Thus, it offers a simple and versatile manner to separate the chemical passivation from the chargeassisted population control at the silicon/dielectric interface. A model is established to obtain the temperature dependence of the capture cross sections, a critical capability for the optimization of the dielectric layers and the investiga... Read More

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Cadmium telluride (CdTe) solar cells represent a commercially successful photovoltaic technology, with an annual production capacity approaching 20 GW. However, improving the opencircuit voltage ( V OC ) remains challenging. This study aims to deepen the understanding of charge carrier recombination in CdTe solar cells and to explore alternative dynamical characterization methods that address the limitations found in conventionally used timeresolved photoluminescence for CdTe solar cells. Transient photovoltage and transient photocurrent techniques are utilized to investigate charge carrier dynamics under conditions resembling realworld solar cell operation. The results reveal that an effective nonradiative recombination lifetime of 580 ns dominates the charge dynamics at V OC values below 850 mV. Above this threshold, radiative recombination becomes significant, with a radiative recombination coefficient of 1.1 10 9 cm 3 s 1 . Additionally, the stationary charge carrier density at 1 sun is determined to be around 1 10 14 cm 3 . By accurately determining both radiative and ... Read More

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Abstract Perovskite solar cells have reached an impressive certified efficiency of 26.1%, with a considerable fraction of the remaining losses attributed to carrier recombination at perovskite interfaces. This work demonstrates how timeresolved photoluminescence spectroscopy (TRPL) can be utilized to locate and quantify remaining recombination losses in perovskite solar cells, analogous to methods established to improve silicon solar cell passivation and contact layers. It is shown how TRPL analysis can be extended to determine the bulk and surface lifetimes, surface recombination velocity, the recombination parameter, J 0 , and the implied opencircuit voltage ( iV oc ) of any perovskite device configuration. This framework is used to compare 18 carrierselective and passivating contacts commonly used or emerging for perovskite photovoltaics. Furthermore, the iV oc values calculated from the TRPLbased framework are directly compared to those calculated from photoluminescence quantum yields and the measured solar cell V oc . This simple technique serves as a practical guide for scr... Read More

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In various types of organic/inorganic solar cells, optical response enhancement is consistently observed within the external quantum efficiency spectra owing to the improvement in interface passivation and the suppression of carrier recombination. In this study, we focused on crystalline silicon solar cells and systematically investigated the impact of interface recombination on the optical response upon dual-side illumination using numerical simulations. The results shed light on the interesting phenomenon that the surface recombination velocity has a significant impact on the external quantum efficiency, and it changes as the illumination direction changes. Moreover, from a practical perspective, the spectra of external quantum efficiency under dual-side illumination conditions can act as a powerful tool for the quick diagnosis of the passivation quality at the top and bottom interfaces.

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Current-voltage measurements are a standard testing protocol to determine the efficiency of any solar cell. However, perovskite solar cells display significant kinetic phenomena that modify the performance at several time scales, due to hysteresis, internal capacitances, and related mechanisms. Here, we develop a method to analyze the current-voltage curves by using large amplitude sinusoids as the excitation waveforms, specifically addressed to determine the influence of cycling frequency on the performance parameters. We solve a system of equations representative of charge collection and recombination, that provide the frequency-dependent dynamical behavior of the internal ion-controlled surface recombination processes that cause open-circuit voltage variations often observed in high performance devices. We analyze several reported experimental data, and we feature the key parameters governing the evolution of hysteresis phenomena as the scan speed is increased in relation to Impedance Spectroscopy.

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The monochromatic absorption coefficient of silicon, inducing the depth of penetration of light into the base of the solar cell, is used through back surface recombination velocity expressions, to determine the optimum thickness necessary for the production of a large photocurrent. The absorption-generation-diffusion and recombination (bulk and surface) phenomena are taken into account in determining the optimum thickness of an n+ -p-p+ bifacial solar cell, for it manufacture process optimization.

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Understanding carrier recombination processes in metal halide perovskites is fundamentally important to further improving the efficiency of perovskite solar cells, yet the accurate recombination velocity at grain boundaries (GBs) has not been determined. Here, we report the determination of carrier recombination velocities at GBs (SGB) of polycrystalline perovskites by mapping the transient photoluminescence pattern change induced by the nonradiative recombination of carriers at GBs. Charge recombination at GBs is revealed to be even stronger than at surfaces of unpassivated films, with average SGB reaching 2200 to 3300 cm/s. Regular surface treatments do not passivate GBs because of the absence of contact at GBs. We find a surface treatment using tributyl(methyl)phosphonium dimethyl phosphate that can penetrate into GBs by partially dissolving GBs and converting it into one-dimensional perovskites. It reduces the average SGB by four times, with the lowest SGB of 410 cm/s, which is comparable to surface recombination velocities after passivation.

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Solar cells are essentially minority carrier devices, and it is therefore of central importance to understand the pertinent carrier transport processes. Here, we advanced a transport imaging technique to directly visualize the charge motion and collection in the direction of relevant carrier transport and to understand the cell operation and degradation in state-of-the-art cadmium telluride solar cells. We revealed complex carrier transport profiles in the inhomogeneous polycrystalline thin-film solar cell, with the influence of electric junction, interface, recombination, and material composition. The pristine cell showed a unique dual peak in the carrier transport light intensity decay profile, and the dual peak feature disappeared on a degraded cell after light and heat stressing in the lab. The experiments, together with device modeling, suggested that selenium diffusion plays an important role in carrier transport. The work opens a new forum by which to understand the carrier transport and bridge the gap between atomic/nanometer-scale chemical/structural and submicrometer optoel... Read More

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The optimum thickness of a silicon solar cell base is determined using phenomelogic parameters, which are the minority carriers diffusion coefficient and the recombination velocity at the back side, influenced by Lorentzs law and the Umklapp process.The results obtained are consistent with the generation of minority charge carriers deep in the base by a monochromatic light of long wavelength.

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Herein, we numerically elucidate the effect of varying surface recombination velocity (S r v ) at the front and back metal contact on the device performance for our reported lead-free formamidinium tin triiodide (FASnI 3 ) perovskite solar cell.The S r v is generally contemplated as a trivial non-radiative recombination loss factor but determinately impacts the characteristics of the solar cell.Given that, we simultaneously varied the S r v at the back and front metal contacts in the range of 1 10 1 -1 10 7 cm/s.Such values for S r v can be realized by ideally passivating the perovskite film and with passivated perovskite films or metallic contact resistive nature.It was inferred that at S r v of 1 10 7 cm/s, the device efficiency was 21.24% and was steeply increased to 21.42% after decreasing the S r v rate to 1 10 1 cm/s, revealing that recombination losses are enhanced at a higher S r v rate because of increased carrier recombination at the defect surface, thereby reducing the efficiency and overall performance of the solar cell.

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Method for determining the volume lifetime of charge carriers in semiconductor substrates, comprising: passivating the substrate surfaces with a first and second passivation structure; characterizing the recombination rate of the passivation structures using a witness substrate with known volume lifetime; measuring the effective lifetime of the substrate; and determining the volume lifetime from the effective lifetime, substrate thickness, and recombination rate.

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Investigations into the temperature dependence of the surface recombination at the interface between silicon and various dielectrics in modern solar cells are of significant interest as they (a) provide fundamental information regarding the interfaces, and (b) allow to improve predictions regarding the performance of solar cells under actual operating conditions. In this study, we use a novel technique based on external bias voltages to control the carrier population at the silicon-oxide/silicon, silicon-nitride/silicon, and aluminum-oxide/silicon interfaces from heavy accumulation to heavy inversion in the temperature range 2590 C. We find that the effective lifetime slightly increases at elevated temperatures when the imbalance of the carrier populations is amplified. In the studied temperature range, it seems that the electron and hole capture cross-sections at all the interfaces are temperature-dependent. The technique offers a simple and versatile manner to separate the chemical passivation from the charge-assisted population control at the silicon/dielectric interface, as a f... Read More

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In this study, we evaluate the effects of perimeter recombination to the performance of GaAs solar cells with different geometries. Two wafers with identical epi-structures were processed into both thin-film and substrate-based devices, which allowed the precise determination of the effect of a rear mirror as well as of the thin-film processing steps to the cells output. In each wafer, a series of solar cells with varying areas was fabricated, and the different contributions to the solar cells dark currents were extracted. We observed that, aside from an expected lower J01, the thin-film devices also showed a larger reduction in illuminated performance with decreasing cell area. From these results, we demonstrate that, in high quality solar cells with low interface recombination velocities and high photon recycling factors, the power output is limited by J02, which is highly affected by perimeter recombination. Therefore, the employment of perimeter passivation techniques might become necessary for these solar cells to achieve higher efficiencies, particularly in small scale applicat... Read More

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The ability to profile and understand carrier concentration throughout thin film absorbers is important to advance solar cell technology. Here, the historical impediments of grain boundary potentials, lateral resistance, and high work functions to such measurements on polycrystalline solar cells are overcome by applying electrochemical capacitance-voltage profiling across the solar cell p-n junction and an electrolyte/semiconductor junction made at the back. Despite the presence of two junctions, modeling indicates that accurate carrier concentrations at the rear of the device can be measured under certain conditions. This is validated by experiments on CdTe solar cells.

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The most significant challenge for environment and renewable energy researchers is to achieve good performance, as well as cost efficiency in terms of solar generators especially in the PV sector. Regarding the thin film solar cells based on Cu(In,Ga)Se2, the present work dissertation is concerned with the performance of a graded band gap solar cell based on (CIGS). The aim is to determine the influence of physical and geometrical parameters on performance. Results indicate that the increase in electric field resulting from the gradient of the band gap dismantles the effects of surface recombination. The results obtained are an efficiency of 26 % for Eg0=1.67 eV, Eg1=1.02 eV and a thickness of layer p and n d1=1m, d2=2m respectively.

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The surface recombination velocity (SRV), which reflects the fundamental characteristics of surface defects of semiconductor wafers, is an important parameter in evaluating the quality of surface passivation and electrical performance of surface devices. In conventional photocarrier radiometry (PCR) used for characterizing the electronic transport properties of electronically thick silicon wafers, the rear SRV usually cannot be determined directly due to the relatively low sensitivity of PCR signal to the rear SRV. On the other hand, the determination of front SRV is also very sensitive to the experimental measurement error, especially the measurement error of instrumental frequency response, which is not always easy to be accurately measured in the experiment. In this paper, the front and rear SRVs of silicon wafers are extracted simultaneously with high accuracy by a differential PCR via multi-parameter fitting of the experimental frequency dependences of amplitude ratio and phase difference of PCR signals obtained from the regular measurements and measurements with wafers being fl... Read More

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In this article, we study the influence of interface and surface recombination effects on the performance of a solar cell and on the photocurrent profile.This study is applied to chalcopyrite thin film solar cell comprising 4 active layers following the model ZnO(n + )/CdS(n)/CuInS2(p)/CuInSe2(p + ) where CuInS2 represents the base and CuInSe2 the substrate.It is based on the continuity equation of charge carriers in semiconductor material and the consideration of certain optical, geometric and electrical parameters (photon absorption coefficient, diffusion length, recombination velocity at the front and the back surface and at the interface between different layers, thicknesses of the layers, etc.).We also consider monochromatic illuminations ranging from visible to near infrared.The results obtained in two-dimensional and three-dimensional representations, show that surface and interface recombination centers can dramatically reduce the efficiency of the collection of carriers for certain wavelength ranges and that the efficiency depends on the area of photon absorption.The photons... Read More

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Method for testing the lifetime of surface state carriers in semiconductors using near-field light excitation and high-frequency ultrasonic detection. The method selectively generates surface carriers through near-field illumination, while high-frequency ultrasonic transducers, laser Doppler vibrometers, and interferometers detect the resulting surface stress waves with nanosecond resolution. By analyzing the stress wave dynamics, the method can isolate and measure the lifetime of surface state carriers, eliminating bulk recombination influences.

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A silicon solar cell (n + /p/ p + ), under monochromatic long-wavelength illumination from the rear face (p + ), corresponding to a low absorption (), is studied in dynamic frequency regime ().The density of photogenerated minority carriers in the base is obtained by solving the diffusion equation provided with the boundary conditions of the surfaces, respectively at the junction (n + /p) and at the back face (p/p + ).The photocurrent density is calculated and represented as a function of the surface recombination velocity (Sf) at the junction, for different values of the modulation frequency ().The two expressions for the dynamic recombination velocity (Sb) at the rear face are deduced as a function of the thickness (H).Moreover, one is dependent on the absorption coefficient of silicon () and the other on the intrinsic parameters of the diffusion D ().Therefore, by making a graphical comparison of the expressions of the dynamic recombination rate, the optimum thickness (Hopt) of the base is extracted for each modulation frequency and modeled in a mathematical relation.Th... Read More

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In this article, a method for obtaining the interface recombination velocity in a solar cell from a measurement of the dark curve is presented. The front interface recombination <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S_f</i> between window and emitter of a GaAs-InGaP heterojunction cell passivated by an AlInP window is used to demonstrate the method. By choosing a proper emitter thickness, the equation for the dark saturation current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> reduces to two terms, one related to the bulk recombination and the other to the interface recombination. The growth direction (either upright or inverted) is found to have a huge influence on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S_f</i> as a result of the formation of an interfacial layer in the inverted grown c... Read More

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In this work, GaAs solar cell has been analyzed by using PC1D simulation software. Optimization of thickness and doping concentration of emitter and absorber layer of solar cell is done. Effect of front and rear surface recombination velocity is analyzed in this work. When surface recombination velocity increases, the value of efficiency decreases due to increase in recombination process. The optimum value of surface recombination velocity are Sn = Sp = 102 cm/s. Front surface reflection is minimized by the use of TiO2 single layer ARC and double layer LiF/HfO2 ARC. Increase in efficiency around 2.71% is achieved as compared to cell without ARC after applying anti-reflection coating of optimum thickness. Simulation results shows GaAs solar cell with efficiency of 26.68%.

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Surface recombination has a great impact on the performance of solar cells and photodetectors, and thus is necessary to be accurately determined. In this paper, a self-normalized photocarrier radiometry (PCR) with mean square variance graph is employed to improve the determination accuracy of the surface recombination velocities of silicon wafers and to reduce the influence of initial values on multi-parameter estimations. In this method data obtained from both the illuminated front surface and the illuminated rear surface are employed. The uncertainties of the estimated carrier recombination parameters, especially for the surface recombination velocities are improved significantly. Moreover, the influence of instrumental frequency response (IFR) on the multi-parameter estimation is totally eliminated. Theoretical simulations and experiments are performed to confirm the theoretical predictions. The estimated average uncertainties of the front and back surface recombination velocities for the sample used are approximately 7.60% and 5.71% by the proposed method, which are much impr... Read More

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A new method of representation based on the generation-decay time (GDT) maps is presented to estimate the recombination dynamic behavior in solar cells. The method quantitively describes the open circuit voltage transients versus carrier density dependence. An accurate estimation of recombination dynamics through GDT maps enables more easily identifying the dominant recombination processes. Moreover, the method provides deeper insight on the consistent interpretation of recombination order and ideality factor.

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We present the surface lifetime characterization of the textured silicon surface for the application in solar cells.The measurement by the Sinton WCT-120 PL lifetime tester is compared with the simulation by the Silvaco TCAD software to get possible values of the surface recombination velocity.The n-type silicon textured surface wafers were used as the substrate.In the first experiment, the carrier lifetime was measured and simulated of the pure textured surface.The second experiment was done after deposition of aluminum oxide by the Atomic Layer Deposition on the textured surface.The thermal method was used with TMA as a precursor.The twodimensional TCAD calculation was realized on the silicon structure with textured surface.The surface profile was determined by the AFM measurement.Two electrodes were placed on both sides of the structure to calculate the current flow generated by the light pulse.The real Sinton optical source spectrum was approximated by the five beams in the range 690 -830 nm with different intensities.The current decrease connected with the decay of the optical i... Read More

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In this article, the front surface field (FSF) passivation of n-type interdigitated back contact (IBC) solar cell was studied and a method to improve the FSF passivation performance of n-type IBC solar cell was proposed. We optimized the phosphorus diffusion on the front surface of IBC solar cell to form a field passivation structure with low surface concentration and shallow junction depth. The surface recombination rate was calculated using EDNA2. Solar cell parameters were simulated by Quokka, and finally we did experiment verification. The results showed that when the deposition time and flow rate of POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> in the phosphorus diffusion process time is 3 min and POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> flow rate is 80 sccm, the front surface saturation current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) is reduced to 3.71 fA/cm <sup xmlns:mml="ht... Read More

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With the progress in device research, the power conversion efficiency (PCE) of perovskite solar cells is continuously improving and is approaching its theoretical limit. Nonetheless, it is still below the efficiency limit predicted by Shockley-Queisser owing to the presence of loss mechanisms. In this paper, we comprehensively analyze the loss factors limiting performance of devices utilizing an equivalent circuit model and identify the dominant loss mechanisms. The results demonstrate that Shockley-Read-Hall recombination and series resistance is the most important two of factors limiting the performance of perovskite solar cell. Shunt resistance and surface recombination plays slight roles in PCE when they are greater than 104cm2 and less than 104cm/s, respectively. Auger recombination has almost no impact on the device performance.

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Abstract Carrier loss mechanisms at microscopic regions is imperative for high-performance polycrystalline inorganic thin-film solar cells. Despite the progress on Kesterite, a promising environmental-benign and earth-abundant thin-film photovoltaic material, the microscopic carrier loss mechanisms and their impact on device performance remain unknown. Herein, we unveil these mechanisms in state-of-the-art Cu 2 ZnSnSe 4 (CZTSe) solar cells using a framework that links microscopic-structural and optoelectronic characterizations with three-dimensional device simulations. The results indicate the CZTSe films have an encouraging intragrain minority carrier lifetime of &gt;10 ns, a marginal radiative recombination loss through sub-band recombination and electrostatic potential fluctuation, whilst a large effective grain boundary recombination velocity of around 10 4 cm s -1 and a low net carrier density of ~110 15 cm -3 . We identify that severe grain boundary recombination and low net carrier density are the current limiting factors of device performance. The established framework can g... Read More

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Abstract Charge transfer (CT) state is a key intermediate to understand recombination processes in organic solar cells (OSCs). In this study, we measured the recombination emission from the CT state under different applied voltages in OSCs and a photocurrent density flowing on the circuit simultaneously. We proposed a photoluminescence (PL) voltage ( V ) plot that is the voltage dependence of PL intensity of the CT state. The PL V plot includes information only from the CT state recombination at the donor/acceptor interface and is complementary to the current density ( J ) V plot that is the most important information for evaluating OSCs. The results demonstrated that the fill factor (FF) of the PL V plot is higher than that of the JV plot, predicting the ideal FF of the device. Our result demonstrated that the simultaneous measurement of photocurrent and recombination emission could be a strong tool for evaluating photoconversion characteristics in OSCs.

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A method for improving the performance of n-type heterojunction solar cells through a novel annealing process that involves illuminating the cell surface with high-intensity light at temperatures above 200°C, while actively cooling the cell to prevent overheating. The process enhances the open-circuit voltage and fill factor of the cells, with improvements attributed to improved surface passivation.

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Non-geminate recombination, as one of the most relevant loss mechanisms in organic and perovskite solar cells, deserves special attention in research efforts to further increase device performance. It can be subdivided into first, second, and third order processes, which can be elucidated by the effects that they have on the time-dependent open-circuit voltage decay. In this study, analytical expressions for the open-circuit voltage decay exhibiting one of the aforementioned recombination mechanisms were derived. It was possible to support the analytical models with experimental examples of three different solar cells, each of them dominated either by first (PBDBT:CETIC-4F), second (PM6:Y6), or third (irradiated CH3NH3PbI3) order recombination. Furthermore, a simple approach to estimate the dominant recombination process was also introduced and tested on these examples. Moreover, limitations of the analytical models and the measurement technique itself were discussed.

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Despite a decade of research, much remains unknown about the role that grain boundaries play in determining the photovoltaic performance of perovskite solar cells. In this talk, I will describe how by combining experimental studies with theoretical device simulations, we find that the recombination at grain boundaries is diffusion limited and depends on the grain area with small grains acting as recombination hot spots. We show that the distribution of grain sizes not only influences the overall performance of perovskite solar cells, but also leads to significant current exchange between small and large grains at open-circuit conditions.

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A comprehensive equivalent circuit model is developed to investigate the surface recombination, bulk recombination, shunt resistance, series resistance and the abnormal hysteresis effect for perovskite solar cells. By comparing the introduced model and the ionic drift-diffusion model, two typical capacitance expressions are summarized to characterize the hysteresis. The proposed equivalent circuit model together with typical capacitance expressions reveals the hidden device physics of solar cells, being a valuable synthesis tool for device simulation and analysis.

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The book presents a comprehensive survey about advanced solar cell technologies. Focus is placed on semiconductor materials, solar cell efficiency, improvements in surface recombination velocity, charge density, high ultraviolet (UV) sensitivity, modeling of solar cells etc. The book references 281 original resources with their direct web links for in-depth reading.

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Thin film solar cells have, in general, three recombination locations that can limit the device performance the bulk, front interface, and back interface. Unfortunately, it is difficult to determine which of these mechanisms limit any given device. Time resolved photoluminescence measurements provide an estimate for the carrier lifetime and, therefore, bulk recombination. Determining the role of the front and back interface in device performance, though, is more complicated. With this in mind, we investigated the use of current densityvoltage measurements with front and back illumination at varying intensities. Using numerical modeling, we show that recombination information about each interface can be gleaned, and the limiting interface can be determined. The response curve signatures learned from modeling are then applied to measurements of real devices.

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This work describes a made home system for measuring electrical properties in solar cells and semiconductor material for photovoltaic application, in an environment with low electrical noise and controlled radiation. It consists of a Faraday cage connected to a source measuring unit (SMU) KEITHLEY 2450, which gets the characteristic curve in solar cells and the resistivity in thin sheets of semiconductor material. The system includes a halogen lamp that allows taking measurements at controlled irradiation. As preliminary results, we have obtained -V curves for solar cells and thin film resistivity at different temperatures in the same system.

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The aim of this work is to present a study of the recombination velocities at the junction initiating the shortcircuit (Sfsc) and limiting the open circuit (Sfoc) of a silicon solar cell under magnetic field in the static regime. From the continuity equation, the density of minority charge carriers in the base, the photocurrent density, and the phototension are determined. The study of the photocurrent density and the phototension, as a function of the junction recombination velocity, makes it possible to determine the recombination velocities at the junction initiating the short-circuit and limiting the open circuit respectively. From the profile of the variation of the photocurrent density and of the phototension as a function of the junction recombination velocity, a technique for determining the junction recombination velocities initiating the short circuit situation and limiting the open circuit is presented.

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Characterisation and optimization of next-generation silicon solar cell concepts rely on an accurate knowledge of intrinsic charge carrier recombination in crystalline silicon. Reports of measured lifetimes exceeding the previous accepted parameterisation of intrinsic recombination indicate an overestimation of this recombination in certain injection regimes and hence the need for revision. In this work, twelve high-quality silicon sample sets covering a wide doping range are fabricated using state-of-the-art processing routes in order to permit an accurate assessment of intrinsic recombination based on wafer thickness variation. Special care is taken to mitigate extrinsic recombination due to bulk contamination or at the wafer surfaces. The combination of the high-quality samples with refined sample characterisation and lifetime measurements enables a much higher level of accuracy to be achieved compared to previous studies. We observe that reabsorption of luminescence photons inside the sample must be accounted for to achieve a precise description of radiative recombination. With t... Read More

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