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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