Back Surface Field Research Articles

Effects of Na doping on the distribution of elements and the formation of back surface field in CIGS absorption layer

Effects of Na doping on the distribution of elements and the formation of back surface field in CIGS absorption layer

Surface Reconstruction for Tin-Based Perovskite Solar Cells

Open-circuit voltage loss and instability from surface Sn(II) oxidation and high-density Sn vacancies pose great hurdles for developing high-performance Sn-based perovskite solar cells (PSCs). Turning attention from the bulk microstructure to surface reconstruction is promising to push the performance enhancement of Sn-based PSCs. Herein, a surface-modulation strategy based on 6-maleimidohexanehydrazide trifluoroacetate is rationally designed to reconstruct the surface structure of FASnI3 films to manage the Fermi level and passivate defects. The electronic state evolution results in an n-type Fermi level shift of the shallow surface, thereby forming an extra back-surface field for electron extraction. Meanwhile, the ion-pairing agent affords passivating cationic and anionic defects, thereby nullifying the charged-defect-rich surface. In particular, the reductive hydrazide group and carboxyl groups alleviate superficial Sn(IV) and inhibit Sn(IV) formation, homogenizing surface potential and prolonging carrier lifetime. Accordingly, devices deliver a champion power conversion efficiency (PCE) of 13.64% and an elongated lifespan, with over 75% of the original PCE after 1000 h of illumination (O2 < 50 ppm). This work presents a new insight on the surface reconstruction strategy for developing high-performance Sn-based PSCs.

P‐Type Nb‐Doped MoS2 Layer for Solar Cell Application

Herein, under a H2S/Ar ambient, a p+‐type Nb‐doped MoS2 (MoS2:Nb) film is developed via a sulfurization for a cosputtered Mo–Nb metal precursor to be applied to chalcogenide thin‐film solar cells. With the [Nb]/([Nb] + [Mo]) compositional ratio, the surface roughness and growth rate increase with the domination and diminishment of the (100) and (002) planes, respectively. By increasing the [Nb]/([Nb] + [Mo]) compositional ratio from 0 to 0.06, simultaneously, the carrier density of the MoS2:Nb films increases from 2.9 × 1016 up to 3.7 × 1020 cm−3, and the conductivity type changes from n‐type to p‐type as a result of the Nb atoms acting as acceptors. The ionization energy indicates a transition from a broad Nb acceptor band to a vacuum level for the highly doped p‐type MoS2:Nb films. Thus, by utilizing the p+‐type MoS2:Nb intermediate layer in the chalcogenide solar cells, a suppressed carrier recombination at the Mo back electrode/chalcogenide absorber interface by a back surface field is expected. Overall, it is believed that the obtained findings in this work can help boost the power conversion efficiency of the chalcogenide solar cells owing to the back junction modification.

Optimization of N-PERT Solar Cell under Atacama Desert Solar Spectrum.

In the Atacama Desert, the spectral distribution of solar radiation differs from the global standard, showing very high levels of irradiation with a particularly high ultraviolet content. Additionally, the response of photovoltaic (PV) technologies is spectrally dependent, so it is necessary to consider local conditions and type of technology to optimize PV devices since solar cells are usually designed for maximum performance under standard testing conditions (STC). In this work, we determined geometrical and doping parameters to optimize the power of an n-type bifacial passivated emitter and rear totally diffused solar cell (n-PERT). Six parameters (the thicknesses of cell, emitter, and back surface field, as well as doping concentration of emitter, base, and back surface field) were used to optimize the cell under the Atacama Desert spectrum (AM 1.08) and under standard conditions (AM 1.5) through a genetic algorithm. To validate the model, the calculated performance of the n-PERT cell was compared with experimental measurements. Computed and experimental efficiencies showed a relative difference below 1% under STC conditions. Through the optimization process, we found that different geometry and doping concentrations are necessary for cells to be used in the Atacama Desert. Reducing the thickness of all layers and increasing doping can lead to a relative increment of 5.4% in the cell efficiency under AM 1.08. Finally, we show the potential effect of metallization and the viability of reducing the thicknesses of the emitter and the back surface field.

Detailed Study on the Role of Nature and Distribution of Pinholes and Oxide Layer on the Performance of Tunnel Oxide Passivated Contact (TOPCon) Solar Cell

Industrial silicon solar cells are now mostly based on aluminum back surface field (Al-BSF) or passivated emitter rear cell (PERC) technologies on p-type crystalline silicon wafers. Recently tunnel oxide passivated contact (TOPCon) solar cell on p-type Si wafers has attracted attention due to its demonstrated higher efficiency than either Al-BSF or PERC type solar cell. Numerical analysis using 3-D Sentaurus Technology Computer Aided Design (3-D-TCAD) software leads to the enhancement of the efficiency of the p- and n-type TOPCon solar cells by optimizing the size, nature, and number density of pinholes in the oxide layer; thickness of the oxide layer with and without pinholes and B doping concentration in the hole selective p+ poly-Si layer at the rear. Effects of both types of pinholes, either completely through (physical contact) or partially through (localized thinner oxide), are studied on cell performance. Simulation results show that pinholes in tunnel oxide have an advantage in lowering of series resistance and improvement of fill factor. To achieve optimum performance, the size, nature, and number density of pinholes and thickness of the oxide layer should be optimized. Considering both types of pinholes, the efficiency achieved is 25.3% for p-TOPCon and 26% for n-TOPCon. Also, the outputs of simulated p-TOPCon are compared with simulated p-PERC solar cell. The analysis shows that TOPCon solar cell on p-type wafer has significant ability to be adopted for industrial production.

Device modeling and study of AZO/i-ZnO/ZnS/CZTS-bilayer solar cell for different series and shunt resistances

The low open-circuit voltage is one of the main reasons to deteriorate the efficiency of copper zinc tin sulfide (CZTS) based solar cells. The double-layer structures (pp+) for CZTS cells are beneficial for reaching high open-circuit voltage due to the presence of the back surface field. Our simulation-based study on ZnS/CZTS-bilayer solar cell reveals the effect of band gap of dual CZTS layers, the thickness of different layers, front and back contact metal work-function, which helps to optimize the solar cell for these parameters. The different experimental conditions and techniques offer a wide range of shunt and series resistance for the fabricated cell. Our device reported the highest efficiency of 20.34% and 20.19% for shunt-series resistance pair of (1424.05 Ω-cm2, 1.97 Ω-cm2) and (840 Ω-cm2, 1.5 Ω-cm2) respectively. The double CZTS layer based device shows an enhancement in cell efficiency compared to a single layer.

Al-Si contact formation involving back surface field and voids of PERC

Local Al–Si contacts are a vital part of passivated emitter and rear cell (PERC) solar cells. They are generally fabricated using laser ablation to open the passivation dielectric layers, which is followed by Al paste printing and high-temperature alloying. However, the alloying process of Al–Si contacts and the formation mechanism of voids remain unclear in parts. In this study, based on the Al–Si binary phase diagram, we revealed the formation path associated with the back surface field (BSF) of the Al–Si alloying process and elucidated the formation mechanism of voids for dashed shape local contact openings. Also, a calculation model is proposed to determine and verify the Si concentration at the peak temperature. During peak-temperature firing, an equilibrium is established between the dissolution and diffusion of Si; subsequently, Si in the melt reaches its saturation concentration and laterally diffuses into the Al layer, thereby causing the net outflow of Si with the contact trench expansion and forming partial voids. During cooling, supersaturated Si precipitates to form BSF, while the degree of precipitated Si limits the thickness and forms the hypereutectic alloy. After the BSF formation, the melt was redistributed along the contact trench, resulting in partial voids turning into complete voids and fully filled contacts. This study also provides a new approach for regulating and optimizing Al–Si contacts. • The formation path of the back surface field of Al Si contact is revealed from the phase diagram. • Silicon saturated at peak temperature and BSF thickness is limited by the degree of silicon precipitation. • The contact of Hypereutectic component Al Si will affect the electrical properties. • The formation of voids is related to the lateral diffusion of silicon and the redistribution of melt. • The redistribution of melt transforms partial voids into complete voids.

Performance Analysis of CZTSe Kesterite Solar Cell by Adding CZTSSe as BSF Layer

Kesterite are chalcogenide materials which is popular for its inexpensive, environment friendly and whose elements are abundantly available. However, its efficiency is less than 12% as it processes high recombination rate. To boost the efficiency of CZTSe kesterite solar cell use of tunable bandgap material CZTSSe as back surface field layer (BSF) prevent the material from these problems. In this analysis, the novel configuration: Mo/CZTSSe/CZTSe/CdS/ZnO/AZO influence of varying compositions S and Se and their parameters are analyzed. The Efficiency, J sc and V oc of the optimized solar cell is investigated to be 33.83%, 56.29(mA/cm2) and 0.689(V) respectively.

Comprehensive cell to module optical loss analysis of metal assisted chemically etched inverted pyramid textured multi-crystalline silicon solar cells and modules by ray-tracing method

Most of the recent articles addressing the texturing issues of diamond wire sawn multi-crystalline silicon (mc-Si) wafers propose metal-assisted chemical etching (MACE) inverted pyramid texturing scheme as the best suited industrial process for the fabrication of low-cost, high efficiency solar cells. However, a detailed generation loss analysis of such textured solar cells are not widely investigated yet, especially after module conversion. We present a comprehensive analysis of various optical losses in MACE inverted pyramid textured mc-Si solar cells and modules using the SunSolve module ray-tracer simulator from PV Lighthouse. The simulation model accurately predicted the optical properties of MACE inverted pyramid textured samples and the simulated reflectance values were nearly identical to experimentally measured values at different stages of solar cell processing (before and after ARC). This study quantifies and benchmarks the optical generation losses of not-encapsulated and encapsulated inverted pyramid textured cells with well established models of random pyramid textured and iso-textured solar cells for aluminum back surface field (Al-BSF) architecture. Moderate cell to module (CTM) generation current loss was noticed for inverted pyramid textured solar cells, which was nearly 0.71 mA-cm−2 lower than random pyramid textured and 1.05 mA-cm−2 higher than iso-textured solar cells. We find that adoption of MACE inverted pyramid texturing over acid texturing enhances the photo-generation in mc-Si modules by ∼0.5% and that the total photo-generation current density in mc-Si solar modules approach 99.6% of that in random pyramid textured c-Si modules.

Impact of ion implantation and annealing parameters on bifacial PERC and PERT solar cell performance

Passivated Emitter and Rear Contact (PERC) and Passivated Emitter Rear Totally Diffused (PERT) solar cell designs are now a market reality. In the production of these cells, ion implantation is another method for creating emitters and back surface field (BSF) regions, since it can facilitate the process flow and precise doping control. Here, Technology Computer Aided Design (TCAD) is utilized to assess the effects of ion implantation fluences, annealing temperature, and duration, on the performance of bifacial PERC solar cells. To ensure realistic simulation results, the solar cell model is developed using experimentally demonstrated bifacial counterparts. The process simulation models are also calibrated to match experimentally obtained doping profiles. Simulation results show that by replacing emitter diffusion with phosphorus ion implantation, both the front/rear efficiencies can be improved by 0.07%. The rear boron implantation is also optimized to provide an effective BSF, improving the front/rear efficiencies by 0.21/0.15%, respectively. Moreover, co-annealing of emitter and BSF regions exhibits a 0.2% increase in efficiency than separately annealed PERT cells. Hence an overall improvement of 0.48/0.42% is achieved in the front/rear efficiencies when compared to the original diffused emitter PERC design. The fabrication process sequence is also suggested for these solar cells.

A qualitative study of SnSe thin film solar cells using SCAPS 1D and comparison with experimental results: A pathway towards 22.69% efficiency

We simulated a tin selenide (SnSe) based solar cell device in a standard planar substrate configuration (glass/Mo/SnSe/CdS/i-ZnO/AZO/Al) using a Solar Cell Capacitance Simulator (SCAPS-1D) software to elucidate a path to higher power conversion efficiency (PCE). A baseline model for the device was simulated and established using the experimental results of our recent study on a 2.51% device. A stepwise fitting procedure observed a higher effective density of states in SnSe, along with a band offset of −0.11 eV for conduction between SnSe and CdS; these factors are responsible for limiting the open-circuit voltage ( V OC ). We optimized the buffer and absorber layer parameters to improve the working capabilities to achieve higher efficiency by improving V OC . In particular, the effects of carrier concentration, absorber–buffer interface recombination, absorber thickness, buffer layer thickness, and defect densities were studied and analyzed in detail via simulation. Interestingly, optimal absorber and buffer layer thicknesses of 1.2 μm and 60 nm were obtained for the baseline and simulated devices. Finally, a NiO back-surface field (BSF) layer was introduced, and its performance was evaluated. Significant improvements in V OC and fill factor (FF) were observed with implementing the NiO BSF layer at the SnSe/CdS interface. The optimal device without a BSF layer exhibited a maximum efficiency of 13.79% with a V OC of 0.590 V; a short-circuit current density ( J SC ) of 36.28 mA cm −2 , and an FF of 64.33%. Finally, the highest PCE of 22.69% with a V OC of 0.818 V, J SC of 33.65 mA cm −2 , and FF of 82.41% was observed after applying the BSF layer. • Simulation of SnSe/CdS-based solar cells using experimental results. • Role of NiO BSF in SnSe/CdS planar heterojunction solar cells. • Importance of VB and CB eDOS to enhance the solar cell performance. • Improvement in the fill factor and open-circuit voltage by introducing a NiO BSF layer.

Numerical simulation and performance optimization of GeSe based thin film solar cell with NiO as back surface field layer

Germanium monoselenide (GeSe) has emerged as a viable candidate for absorber material in thin film solar cell (TFSC) due to its favorable material characteristics. Herein, the novel GeSe based TFSC with CdS as buffer layer and NiO as back surface field (BSF) layer has been proposed and its photovoltaic performance has been evaluated theoretically using wxAMPS software. The device output parameters have been assessed by varying thickness and carrier concentration for the GeSe layer, CdS layer and NiO layer, respectively. Moreover, the defect densities in GeSe absorber layer, CdS/GeSe and GeSe/NiO interface layers, and the work function of metal electrode at the cell rear side have been altered to evaluate the photovoltaic characteristics. Conversion efficiency of 31.37% has been obtained for the proposed GeSe-based TFSC with the new architecture under the conditions such as the thicknesses of the CdS layer, GeSe layer and NiO layer are optimized to be 0.03 μm, 0.3 μm and 0.05 μm, respectively; the carrier concentrations of the CdS layer, GeSe layer and NiO layer are optimized to be 1018 cm−3, 1019 cm−3 and 1020 cm−3, respectively; the defect densities in the GeSe layer, IDL1, IDL2 both are set to be 1015 cm−3. These results suggest that GeSe can be employed as the promising absorber layer to fabricate low-cost and high efficiency TFSC.

UV‐induced degradation of high‐efficiency silicon PV modules with different cell architectures

AbstractDegradation from ultraviolet (UV) radiation has become prevalent in the front of solar cells due to the introduction of UV‐transmitting encapsulants in photovoltaic (PV) module construction. Here, we examine UV‐induced degradation (UVID) in various commercial, unencapsulated crystalline silicon cell technologies, including bifacial silicon heterojunction (HJ), interdigitated back contact (IBC), passivated emitter and rear contact (PERC), and passivated emitter rear totally diffused (PERT) solar cells. We performed UV exposure tests using UVA‐340 fluorescent lamps at 1.24 W·m−2 (at 340 nm) and 45°C through 4.02 MJ·m−2 (2000 h). Our results showed that modern cell architectures are more vulnerable to UVID, leading to a significant power decrease (−3.6% on average; −11.8% maximum) compared with the conventional aluminum back surface field (Al‐BSF) cells (&lt;−1% on average). The power degradation is largely caused by the decrease in short‐circuit current and open‐circuit voltage. A greater power decrease is observed in bifacial cells with rear‐side exposure compared with those with front‐side exposure, indicating that the rear side is more susceptible to UV damage. Secondary ion mass spectroscopy (SIMS) confirmed an increase in hydrogen concentration near the Si/passivation interface in HJ and IBC cells after UV exposure; the excess of hydrogen could result in hydrogen‐induced degradation and subsequently cause higher recombination losses. Additionally, surface oxidation and hot‐carrier damage were identified in PERT cells. Using a spectral‐based analysis, we obtained an acceleration factor of 5× between unpackaged cells (containing a silicon nitride antireflective coating on the front) in the UV test and an encapsulated module (with the front glass and encapsulant blocking 90% of the UV at 294 nm and 353 nm, respectively) in outdoor conditions. From the analytical calculations, we show that a UV‐blocking encapsulant can reduce UV transmission in the module by an additional factor of ~50.

Numerical modeling of ultra-thin CuSbS2 heterojunction solar cell with TiO2 electron transport and CuAlO2:Mg BSF layers

The ternary chalcostibite copper antimony sulfide (CuSbS2) system, with its very high optical absorption coefficient, low-cost, vacuum-free fabrication techniques, and earth-abundant elements, is a rising candidate as solar absorber material for ultrathin film solar cells. However, due to the Schottky barrier formed at the back-contact and high carrier recombination at the CuSbS2/CdS interface, the efficiency of conventional CuSbS2/CdS heterojunction solar cell is very poor. This article proposes titanium dioxide (TiO2) as an alternative to CdS layer for the CuSbS2-based thin film solar cells (TFSCs). Using TiO2, CuSbS2, and Mg-doped CuAlO2 (CuAlO2:Mg) as an electron transport layer (ETL), absorber layer, and back-surface field (BSF) layer, respectively, a novel (Al/ITO/n-TiO2/p-CuSbS2/p+-CuAlO2:Mg/Au)-based npp+ heterojunction solar cell has been designed and simulated by SCAPS-1D solar cell simulator. The effects of integrating the CuAlO2:Mg BSF layer on the PV responses of the CuSbS2-based heterojunction solar cell in terms of the built-in potential and the back-contact carrier recombination have been studied. In addition, an investigation on the influences of various device parameters viz. carrier concentration and thickness of each layer, back-contact metal work function, shunt and series resistance, and working temperature have been carried out systematically. The results are analyzed in correlation with the PV parameters of the device to optimize the efficiency of the proposed solar cell. The optimized CuSbS2-based solar cell shows good performance stability at high temperature, with a maximum efficiency of 23.05% (Voc = 969 mV, Jsc= 34.61 mA/cm2, FF = 68.71%).

Numerical investigation of the Cu2O solar cell with double electron transport layers and a hole transport layer

In this paper, a model of the Cu2O solar cell with double electron transport layers (ETLs) and a hole transport layer (HTL) has been investigated by SCAPS. Compared to the single ETL of ZnO, the problem of low open circuit voltage of the Cu2O solar cells can be improved by introducing the double ETLs of Zn(O,S)/ZnS. Our simulation results show that the sulfur concentration of Zn(O,S) and the donor density in double ETLs have a significant effect on device performance. The optimum S/S + O ratio and the best donor density are 0.82 and 8 × 1017cm−3, respectively. Due to the formation of an electron reflector and back surface field (BSF), an enhancement in both short circuit current density and open circuit voltage can be realized by introducing an appropriate HTL, and the best HTL is CuI, showing an efficiency of 12.15%. Then, the work function of metal electrode, the Cu2O thickness, the defect density and the acceptor density of Cu2O absorber layer, and the defect density at the Cu2O interfaces have been systematically investigated. After optimization, the best device efficiency of 16.49% can be achieved. Our results have demonstrated a new high-efficiency structure for cuprous oxide solar cells.

Comparison of different passivation layers for GaInAs solar cells grown by solid-source molecular beam epitaxy

Ga0.47In0.53As (hereafter, GaInAs) solar cells with a 0.74 eV bandgap were grown by solid-source molecular beam epitaxy (MBE) using different passivation layer combinations. Al0.48In0.52As (hereafter, AlInAs) and InP with 1.50 and 1.35 eV bandgaps, respectively, are promising candidates for use as passivation layers. Since As2 and P2 are used in GaInAs/InP heteroepitaxy, the effect of exposing the InP and GaInAs surfaces to As2 and P2 fluxes was evaluated before the GaInAs solar cell growth to improve the heterointerface quality. It was found that an exposure time of 10 s was sufficient to obtain clean heterointerfaces by minimizing the As–P exchange reaction on each surface. Regarding the solar cell performance, by implementing an InP window and AlInAs back-surface field layers on a GaInAs solar cell, the recombination at both the front and rear surface can be effectively reduced. Consequently, 13.04% conversion efficiency with a 394 mV open-circuit voltage was obtained. This is the highest efficiency ever achieved in an MBE-grown GaInAs solar cell on InP.

New theoretical analysis of a novel hetero-junction SnS/CdS solar cell with homo-junction P–P+ in the rear face-numerical approach

The numerical investigation on a solar cell based on SnS was carried out in this paper utilizing SCAPS-1D simulation software. The originality of this work lies in the top efficiency reached after adding a BSF of the same type of absorber layer. Studied photovoltaic solar cell is wrought of a SnS layer, one layer of cadmium sulfide CdS, and ITO as a TCO layer. To achieve optimal performance, the impact of layer thicknesses, carrier concentration, series and shunt resistance, operating temperature, and the impact of the SnS P+ layer as a back surface field on solar cell performance were examined. With the insertion of the BSF in the proposed cell, the open-circuit tension improved from 820 to 930 mV, the Jsc current density slightly increased from 34.75 to 35.09 mA/cm2, the FF Fill Factor increased by even more than 87%, and a top efficiency of 28.47% was reached so rather than 23.94%.

22.8% efficient ion implanted PERC solar cell with a roadmap to achieve 23.5% efficiency: A process and device simulation study

Among all available photovoltaic (PV) technology options, c-Si based passivated emitter rear cell (PERC) has already proved its mettle by delivering more than 22% conversion efficiency at the industrial level. However, designing of PERC solar cell device remains a challenge owing to recombination and absorption losses, which eventually restrict the performance of the device toward achieving an Auger efficiency limit of 29.4%. The primary contributor to these losses is emitter recombination losses that limits the performance of PERC devices. The n+-emitter region in the proposed PERC devices is formed using ion implantation followed by a diffusion process. The impact of process variables such as dose (cm−2), energy (keV), diffusion time (s), and diffusion temperature (oC) on the PERC device performance is not much explored. Therefore, in an attempt to fulfill this research gap, the emitter region performance in terms of ion implantation of phosphorus, influence of local back surface field (BSF) doping concentration (1017 to 1019 cm−3), and back surface recombination velocity (SRV 101–107 cm/s) on PERC device performance followed by the loss analysis is examined in this work. An upright pyramid textured structure with constant height (5 μm) and industrial standard stacked dielectric anti-reflective coating layers, SiNX/SiO2 and Al2O3/SiNX at front and back side respectively is realized using different process statements such as deposit, etch, implantation, and diffusion with the help of a Silvaco TCAD software. Investigations reveal that the PERC device can deliver an efficiency of 22.8% with 150 μm boron-doped crystalline silicon (c-Si) wafer at an optimum phosphorous dose (5 × 1015 cm−2), BSF doping (1019 cm−3), and SRVn (107 cm/s). Short-circuit current density (JSC) of 40.8 mA/cm2, open-circuit voltage (VOC) of 0.686 V, and fill factor (FF) of 81.54% are obtained for the structure under consideration. A roadmap to achieve 23.5% conversion efficiency has also been reported by assuming a carrier selective contact at the backside with a surface recombination velocity of 10 cm/s.

Device physics of homojunction perovskite solar cells: a design omitting all the charge transport layers with efficiency exceeding 26.3%

Perovskite solar cells (PSCs) omitting all the charge transport layers with p–n homojunction structure are considered a promising alternative for commercialization owing to their low fabrication cost and simplified structure. Deep understanding of the device physics of these all-free p–n homojunction structured PSCs is of paramount importance. Here, a thorough investigation of all-free perovskite–perovskite p–n homojunction structured PSCs is performed by using a photoelectrical coupling model. Four different configurations including a standard n–i–p cell, electron transport layer-free cell, hole transport layer-free cell, and all-free cell are compared to identify the limiting performance factors, and the results indicate that no extra built-in electric field in the perovskite layer and severe surface recombination occurring at the perovskite interface are the two main factors limiting the power conversion efficiency (PCE) of all-free p–n homojunction structured PSCs. Based on doping engineering, a highly efficient all-free p–n homojunction structure is designed, which consists of an asymmetric p–n junction with both a front surface field layer and a back surface field layer. The effects of optical loss, thickness of the emitter, doping concentration for both the emitter and base, and diffusion length on the performance of p–n homojunction structured PSCs are optimized. After optimization, the PCE of the all-free p–n homojunction structured PSCs reaches 26.33%, which is slightly higher than that of a standard n–i–p heterojunction cell (26.22%). This work demonstrates that all-free p–n homojunction structured PSCs are a promising alternative to standard n–i–p heterojunction structured PSCs for realizing high efficiency, which may pave the way toward commercialization of PSCs in the future.

Contribution to the study of a CdS / CZTS-based solar cell with a gradual BSF layer

Thin-film solar cells are currently the subject of several research works aimed at achieving the best relationship between energy and cost efficiency. The objective of this work is to improve the performance of a thin film solar cell based on CdS / CZTS by introducing a gradual layer on the back surface (Back Surface Field) in order to reduce the recombination losses in the back face and therefore increase the efficiency of photovoltaic conversion. The results obtained show that the addition of a back surface field (BSF) has a remarkable influence on the characteristics and the electrical performance of the solar cell. This results into an improvement in the values of the short-circuit current and of the opencircuit voltage, as well as the conversion efficiency with acceptable quantities. This study shows that, for an absorbent layer thickness of 2.42 µm, the BSF layer improves the photovoltaic conversion efficiency from 16.93% (cell without BSF) to 18.5% (for a cell with BSF).