Rear Interface Research Articles

Effect of ultra-thin ZnS passivation using ALD technique on the performance of heterojunction solar cells

Hybrid solar cells (HSCs) using poly (3,4-ethylenedioxy-thiophene) polystyrene sulfonate (PEDOT:PSS) and n-silicon provide heterojunctions with the potential of light trapping, cost effectiveness, and high efficiency. However, charge recombination at rear interface hampers built-in potential and power conversion efficiency (PCE). Here, a superior, conformal, and uniform ultra-thin layer of Zinc sulfide (ZnS) is deposited on rear interface using atomic layer deposition (ALD) technique. The ALD-deposited ZnS thin layer serves as a passivation, electron conductive, and hole-blocking layer. The optimized HSCs exhibit a remarkable PCE of 12.37 % alongside a high open-circuit voltage of 0.625 V and a substantial fill factor of 71.5 %. These advancements stem from enhanced back junction quality between n-Si and electrode. The outcomes demonstrate an effective suppression of charge recombination and enhanced charge transfer facilitated by ALD-deposited ZnS thin layer, resulting an improved photovoltaic performance.

Probing the Impact of Four BSF Layers on MASnI3‐Based Lead‐Free Perovskite Solar Cells for >33% Efficiency

AbstractThis study systematically investigates the impact of various layers of the back surface field (BSF) on the performance of CH₃NH₃SnI₃ (MASnI₃)‐based lead‐free mixed organic–inorganic halide perovskite solar cells. By employing SCAPS‐1D (Solar Cell Capacitance Simulator in One Dimension) simulation software, the behavior of solar cells is analyzed incorporating BSF layers of CuI, NiO, ZnTe, and CBTS. The findings indicate that the inclusion of these BSF materials significantly enhances power conversion efficiency (PCE), with CBTS showing the highest PCE of 33.57%. The energy band diagrams reveal that the BSF layers effectively reduce recombination losses at the rear interface and improve charge carrier collection. Detailed analysis of photovoltaic parameters, such as open‐circuit voltage (Voc), short‐circuit current density (Jsc), fill factor (FF), and overall PCE, underscores the superiority of CBTS as optimal BSF materials. Temperature variation studies demonstrate that CBTS maintains superior performance across a range of temperatures, highlighting its potential for high‐efficiency, thermally stable perovskite solar cells. This comprehensive investigation provides valuable insights for optimizing the design and performance of MASnI₃‐based perovskite solar cells, with the aim of efficiencies greater than 33%.

Effects of Al2O3 Rear Interface Passivation on the Performance of Bifacial Kesterite‐Based Solar Cells with Fluorine‐Doped Tin Dioxide Back Contact

Herein, ultrathin Al2O3 is investigated as a rear interface passivation layer for kesterite solar cells with F:SnO2 (FTO) back contact for potential performance improvement. On the passivation layer, a thin Mo layer is deposited to improve the FTO's ohmicity. Further, NaF is evaporated on the copper zinc tin sulfide (CZTS) precursors to create openings at the passivation layer and achieve Na‐induced benefits in the absorber. The CZTS absorbers deposited directly on the Al2O3‐coated FTO peel off, while those with Mo interlayer do not. For pure sulfide kesterite devices, the Al2O3 layer reduces the short‐circuit current density (JSC), resulting in poor device efficiency. On the other hand, significantly higher JSC is realized for mixed sulfide and selenide kesterite devices with Al2O3 passivation layer, with the current density–voltage curve suggesting a reduced barrier height at the rear interface. As a result, the efficiency is improved from 1.5% for devices without Al2O3 to 4.6% for those with Al2O3. Likewise, improved external quantum efficiency response is observed in the devices with passivation layer for backside and frontside illumination. Therefore, contribution of Al2O3 passivation layer to the performance of kesterite‐based solar cells is evident from the results of this study.

Design of MoO3 Porous Back Contact for High Efficiency CZTSSe Thin-film Solar Cells

The introduction of in-situ anodized MoO3 porous arrays with tailored structural parameters as the rear interface contact has a positive impact on enhancing the solar cell performance. The optimized device efficiency increased from 6.31% to 9.00% (in reference to molybdenum-based cells), resulting in a 32% increase in JSC and a 64% increase in FF. The results indicate that at a 10V oxidation voltage, the MoO3 pore size is relatively larger, facilitating the formation of a well-interpenetrating structure and contact interface with CZTSSe. In turn, assists in carrier interface separation and transfer, effectively suppressing the recombination of separated carriers. It extends carrier lifetime, reduces band tailing effects, and lowers urbach energy, thus improving the overall performance of CZTSSe devices.

Simulation‐Based Performance Analysis of Lead‐Free Bismuth Perovskite Solar Cells: A Comparative Study of Cs3Bi2I9 and (CH3NH3)3Bi2I9 ‐based Perovskite Solar Cells

AbstractPerovskite solar cells (PSCs) have emerged as promising candidates in PV research due to their exceptional photovoltaic properties. However, the toxicity and environmental concerns associated with lead‐based perovskites have led to the exploration of lead‐free alternatives. In this study, the performance of lead‐free bismuth PSCs, specifically PSCs based on Cesium Bismuth Iodide (Cs3Bi2I9) and Methyl Ammonium Bismuth Iodide (MA3Bi2I9), is investigated. Numerical simulations using the solar cell capacitance simulator (SCAPS) are conducted to comprehensively analyze the influence of key parameters, including the band‐to‐band radiative recombination rate, the absorber layer defect density, the absorber layer/electron transport layer (ETL) interface defect density, the absorber layer/hole transport layer interface (HTL) defect density, operating temperatures, and series and shunt resistances, and to optimize the proposed PSCs accordingly. The simulation results demonstrate a significant impact of these key parameters on the performance of Cs3Bi2I9 and MA3Bi2I9 PSCs. The optimized Cs3Bi2I9‐based PSC exhibited notable performance characteristics, including a PCE of 13.81%, a Voc of 1.16 V, a Jsc of 18.14 mA cm−2, and FF of 65.51%. In contrast, the MA3Bi2I9‐based PSC demonstrated relatively lower performance, with a PCE of 11.82%, Voc of 1.14 V, Jsc of 18.06 mA cm−2, and FF of 57.33%. The study on the defect density at the interfaces revealed the performance of PSCs is predominantly influenced by defects at the front interface (ETL/Absorber) rather than the rear interface (HTL/Absorber). These results provide valuable insights for the experimental design and optimization of lead‐free bismuth PSCs.

Hydraulic fracturing in layered heterogeneous shale: The interaction between adjacent weak interfaces

Shale is known as the typical layered heterogeneous rock with multiple weak interfaces between different layers, and how to depict the propagation characteristic of fluid-driven fracture in such complex geological structures is critical for hydraulic fracturing engineering. Traditional investigations only focus on the intersecting behaviors of hydraulic fracture (HF) at a single weak interface. Herein, we reveal the propagation of HF in shale formation based on the extended finite element method (XFEM), where multiple weak interfaces and different rock properties are carefully considered in the sandwiched layered structure (SLS). The crack tip singularities at the weak interfaces due to the material discrepancy are characterized by the eigen-function expansion, and the unified enrichment function is constructed to evaluate the stress intensity factors (SIFs) directly without extra computations. The corresponding energy release rate (ERR) criteria are employed to determine the HF propagation direction. By the comprehensive analysis with various dip angles and material/structural properties, the propagation of HF moving across the layered heterogeneous shale is regarded as the interaction between adjacent weak interfaces. For the front weak interface, the inhibition effect could be seen in the fracture penetrating capacity by the rear interface, which reflects contrasting trends due to large material discrepancies of various weak interfaces. The propagation behavior at the rear weak interface is affected by the facilitation effect from the front interface, and the HF pre-offset at the front interface greatly enhances the facilitation effect on fracture penetrating through shale formations.

Development of a Plasmonic Light Management Architecture Integrated within an Interface Passivation Scheme for Ultrathin Solar Cells

In response to climate and resource challenges, the transition to a renewable and decentralized energy system is imperative. Ultrathin Cu(In,Ga)Se2 (CIGS)‐based solar cells are compatible with such transition due to their low material usage and improved production throughput. Despite the benchmark efficiency of CIGS technology, ultrathin configurations face efficiency drops arising from increased rear interface recombination and incomplete light absorption. Dielectric passivation schemes address rear interface recombination, but achieving simultaneous electrical and optical gains is crucial for thinning down the absorber. Plasmonic nanoparticles emerge as a solution, enhancing light interaction through resonant scattering. In the proposed architecture, the nanoparticles are encapsulated within a dielectric rear passivation layer, combining effective passivation and light trapping. A controlled deposition and encapsulation of individualized nanoparticles is achieved by an optimized process flow using microfluidic devices and nanoimprint lithography. With the developed plasmonic and passivated architecture, a 3.7 mA cm−2 short‐circuit current density and a 23 mV open‐circuit voltage improvements are obtained, leading to an almost 2% increase in light‐to‐power conversion efficiency compared to a reference device. This work showcases the developed architecture potential to tackle the electrical and optical downfalls arising from the absorber thickness reduction, contributing to the dissemination of ultrathin technology.

Impact of Band‐gap Gradient in Semi‐Transparent and Bifacial Ultra‐Thin Cu(In,Ga)Se2 Solar Cells

AbstractUltra‐thin Cu(In,Ga)Se2 (CIGSe) solar cells on transparent conductive oxide back contact reduce the material consumption of rare indium and gallium and simultaneously exhibit great potential for semi‐transparent bifacial application. For highly efficient CIGSe solar cells, a steep back Ga grading and Na treatment are expected. However, Na will promote the formation of highly resistive GaOx at the rear interface owing to Ga accumulation. In this work, the three‐stage co‐evaporation process is renewed and the effect of the deposition sequence in the first stage on the Ga distribution as well as the cross‐correlated influence of Na is explored. In particular, the standard deposition sequence of Ga+In is altered to start with In. When a thin In layer is pre‐deposited on the back contact, the fill factor and efficiency increase. The deposition of In+Ga+In in the first stage of CIGSe growth leads to efficiencies 28% (on average) higher than for the standard deposition sequence of Ga+In. Additionally, 2.74% efficiency is reached under rear and 9.32% under simultaneous front and rear illumination. Therefore, adapting the deposition sequence in the first stage of CIGSe growth is identified as a key to improving the device performance on transparent back contact.

Toward improving the performance of Cu2ZnSnS4-based solar cells with Zr, W or sulfurized layers at the SnO2:F/Cu2ZnSnS4 rear interface

The photovoltaic performance of Cu2ZnSnS4 (CZTS)-based thin film solar cells with transparent back contacts is mainly constrained by the ohmic loss due to degradation of the back contacts at high temperatures required for the growth of the CZTS absorbers. This work has attempted to use ultrathin Zr and W interlayers at the SnO2:F (FTO)/CZTS interface with the purpose of improving the ohmic properties of FTO and hence the performance of solar cells. 20 nm thick Zr and W layers were coated on FTO using direct current magnetron sputtering, followed by heating at 550 °C in a sulfur atmosphere for some of the samples. Inclusion of Zr and W interlayers compromised the transmittance of the FTO back contact, however heating of the samples in a sulfur atmosphere improved the transmittance to values comparable to or better than those of un-heated FTO. Furthermore, heated W/FTO showed a significant improvement in electrical conductivity as observed from Hall effect measurements. To make complete solar cells, CZTS absorber, buffer (CdS) and window (i-ZnO/ZnO:Al) layers were sequentially deposited on the un-heated FTO, Zr/FTO, W/FTO and Mo back contacts. Glow discharge optical emmision spectroscopy confirmed that Zr and W did not diffuse into the absorber and also prevented Na diffusion into the absorber. From the scanning electron microscopy cross sectional analysis, an impovement in the absober grain size and a clear junction between the absorber and FTO with W interlayer were observed. Grazing incident X-ray diffractometry confirmed the polycrystalline nature of the CZTS thin films and indicated the presence of other phases, particularly SnS2. On the resulting solar cell parameters, the inclusion of a W interlayer reduced the series resistance from 4.5 Ωcm to 3.7 Ωcm2. An improvement in short circuit current density (JSC) is also observed, enhancing the efficiency of the solar cells with CZTS/W/FTO to 3.1 % compared to that with CZTS/Mo at 2.7 % and CZTS/FTO at 3.0 %. W was found to improve the external quantum efficiency response and JSC of the solar cells for both backside and frontside light illumination. On the other hand, inclusion of a Zr interlayer (Zr/FTO) only slighlty improved the open circuit voltage, but compromised the JSC compared to FTO and W/FTO back contacts. Thus, the findings of this study demonstrate the prospect for improving the performance of the CZTS-based thin film solar cells through the inclusion of ultrathin Zr and W interlayers between the FTO back contact and CZTS absorber.

Rear Surface Passivation for Ink‐Based, Submicron CuIn(S, Se)2 Solar Cells

AbstractA N, N‐dimethylformamide and thiourea‐based route is developed to fabricate submicron (0.55 and 0.75 µm) thick CuIn(S,Se)2 (CISSe) thin films for photovoltaic applications, addressing challenges of material usage, throughput, and manufacturing costs. However, reducing the absorber film thickness below 1 µm in a regular CISSe solar cell decreases the device efficiency due to losses at the highly‐recombinative, and mediocre‐reflective Mo/CISSe rear interface. For the first time, to mitigate the rear recombination losses, a novel rear contacting structure involving a surface passivation layer and point contact openings is developed for solution processed CISSe films and demonstrated in tangible devices. An atomic layer deposited Al2O3 film is employed to passivate the Mo/CISSe rear surface while precipitates formed via chemical bath deposition of CdS are used to generate nanosized point openings. Consequently, Al2O3 passivated CISSe solar cells show an increase in the open‐circuit voltage (VOC) and short‐circuit current density when compared to reference cells with equivalent absorber thicknesses. Notably, a VOC increase of 59 mV contributes to active area efficiencies of 14.2% for rear passivated devices with 0.75 µm thick absorber layers, the highest reported value for submicron‐based solution processed, low bandgap CISSe solar cells.

Improvement and structure optimization of transmission-mode GaAs photocathode performance

In order to improve the performance of transmitted GaAs photoelectric cathode, the quantum efficiency curve of Chinese transmitted GaAs photoelectric cathode is compared with that of the product of American ITT company, showing that the integration sensitivity of Chinese transmitted photoelectric cathode is 2130 μA/lm, and the American ITT company’s reaches 2330 μA/lm. Through the matrix method to solve the three membranes, the theoretical reflectivity is obtained. Based on the uniform doping transmission GaAs photocathode quantum efficiency formula, by replacing the fixed value <i>R</i> with variable value <inline-formula><tex-math id="M1">\begin{document}$ {R}_{{\mathrm{t}}{\mathrm{h}}{\mathrm{e}}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231542_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231542_M1.png"/></alternatives></inline-formula>, adding the short wave constraint factor, and modifying the quantum efficiency formula, a modified uniform doping transmission GaAs photocathode quantum efficiency formula is obtained. Using the revised quantum efficiency, optical performance and integral sensitivity theory model, through fitting the quantum efficiency curve of American ITT company product , introducing the ITT cathode component performance parameters, comparing the performance parameters of Chinese product, the results show that the Chinese photocathode in the window layer, the thickness of the emission layer, electron diffusion length and rear interface composite rate has a certain gap with ITT’s. In order to shorten the gap between the two and optimize the cathode structure parameters, the transmission GaAs photocathode optical structure software is designed to further analyze the influence of the electron diffusion length and the emission layer thickness on the quantum efficiency of the photocathode. The results show that with an electron diffusion length of 7 μm and emission layer thickness of 1.5 μm, the transmitted GaAs photocathode sensitivity can be more than 2800 μA/lm. However, the large electron diffusion length has high requirements for cathode materials and preparation level. The reasons responsible for the performance gap between Chinese product and other country’s are that in China the growth process of cathode materials is not jet matureand the cathode preparation equipment is out of date . In this paper, we study the relationship between GaAs photocathode optical performance and photoemission performance, and further optimize the structural design of cathode components, which has certain guiding significance for improving the cathode quantum efficiency and the level of image intensifier.

Achieving highly efficient kesterite solar cells using simultaneous surface Ge substitution and rear interface engineering strategies

The progress in the device performance of kesterite-based thin-film solar cells (TFSCs) have been stagnant due to unstable rear contact properties and large open circuit voltage (Voc)-deficit characteristics. Several individual strategies have been developed to solve these issues. In this work, we investigate the simultaneous impact of Ge substitution and rear interface engineering with a MoOx intermediate layer on Mo back contact. The simultaneous application of both strategies delivers a synergetic effect, improving microstructure, Voc-deficit, band-tailing states, and device parameters and reducing Sn-related deep-level defects, resulting in enhanced power conversion efficiency (from 8.1 to 11.55%). This effective strategy offers new insight and a way to solve unstable rear contact properties and large Voc-deficit, further improving the device performances of kesterite-based TFSCs.

Improving the minority carrier lifetime of PERC solar cells via bi-layer rear interface passivation strategy

Passivated emitter and rear contact (PERC) based solar cells are dominating the current photovoltaic (PV) market due to their high power conversion efficiency (PCE) and low cost. However, issues like the lower minority carrier lifetime (MCLT) and high density of surface dangling bonds are limiting their further improvement in PCE. To overcome this issue, a bi-layer rear interface passivation strategy is developed with the ultra-thin Al2O3 and SiO2 layers in PERC solar cells. Applying single (Al2O3) and double (SiO2/Al2O3) passivation layers revealed that each process parameter such as plasma conditions, deposition temperature, post-annealing temperature, and the film thickness in the ALD process affect the MCLT values as well as overall device performance. Especially, post-annealing treatment which improves crystallinity, and reduces interfacial defects was found to be most influential for the MCLT value. The single Al2O3 layer applied in PERC solar cells revealed an increase and decrease in MCLT values at a relatively lower (<10 nm) and higher thickness (>15 nm), respectively. Further, integration of SiO2 with the Al2O3 layer showed its more prominent effect than just single Al2O3 and SiO2 passivation layers. An optimal SiO2 thickness combination (4 nm) with an Al2O3 layer (12 nm), demonstrated reduced density of surface dangling bonds and diffusion of Al atoms from Al2O3 layers. As a result, it improved the carrier extraction yield by increasing the negative fixed charge. Finally, SiO2/Al2O3 (4/12 nm) double passivation layer post-annealed at 450 °C for 15 min delivers improved PCE from 19.4% to 19.9% in PERC solar cells.

Rear Interface Engineering in Solution‐Processed Submicron Cu(In,Ga)(S,Se)2 Solar Cells on Transparent Sn:In2O3 Back Contact

AbstractThe parasitic absorption in Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells emerging from the Mo back contact can be significantly reduced by replacing it with tin‐doped indium oxide (ITO). Commonly, an undesirable GaOx layer forms at the CIGSSe/ITO interface during the high‐temperature fabrication process, which has a detrimental effect on photo‐carrier extraction. Here, a Cu‐In‐TU‐DMF (TU: thiourea, DMF: N, N‐Dimethylformamide) intermediate layer for modification of the CIGSSe/ITO interface, which improves the efficiency of submicron CIGSSe solar cells significantly, is reported about. The reference submicron CIGSSe solar cells exhibit inferior performance (2.4% efficiency) and a large open circuit voltage deficit (Voc,def = 815.9 mV) due to a high barrier at the CIGSSe/ITO interface. At the modified rear interface, the recombination is reduced and hence carrier transport and collection are obviously improved. The efficiency of submicron CIGSSe solar cells on ITO with rear interface modification achieves 7.9% with an open circuit voltage of 565.8 mV, a short circuit current density of 23.4 mA cm−2, and a fill factor of 59.5%, as well as a Voc,def of 589.2 mV.

The formation of bioaerosols in the reopening of an occluded airway

The reopening of an occluded airway can lead to the formation of droplets and aerosols, which can be released during exhalation, providing a possible mechanism of disease transmission. In this study, the flow behavior of airway occlusions (“plugs”) close to their point of rupture is examined using a free-surface model (volume of fluid), such that factors influencing the formation of droplets during their reopening can be identified. The propagation of airway occlusions is highly influenced by recirculating flow at the edge of the front interface, where significant fluctuations of wall shear stresses occur. The resulting drag force causes the rear interface to advance at a greater rate, destabilizing the plug. As the plug thickness decreases, a thin film with uniform thickness forms, resulting in a disk-like structure around the centerline. Rupture occurs around the disk formation largely due to surface tension instability. At lower pressures, smaller disks form causing the rupture to occur through a puncture point (forming no droplets); at higher pressures, a larger disk forms, with rupture occurring along the disk edge and at the center (forming multiple droplets). Upon reopening, a jet of air is produced, causing a temporary increase in shear stress along the wall. However, the magnitude and duration of this increase do not scale directly to the applied pressure, as the formation of droplets and irregularities in airway lining were found to disrupt the flow field and the shear stresses at the wall.

Over 100 mVVOCImprovement for Rear Passivated ACIGS Ultra‐Thin Solar Cells

AbstractA decentralized energy system requires photovoltaic solutions to meet new aesthetic paradigms, such as lightness, flexibility, and new form factors. Notwithstanding, the materials shortage in the Green Transition is a concern gaining momentum due to their foreseen continuous demand. A fruitful strategy to shrink the absorber thickness, meeting aesthetic and shortage materials consumption targets, arises from interface passivation. However, a deep understanding of passivated systems is required to close the efficiency gap between ultra‐thin and thin film devices, and to mono‐Si. Herein, a (Ag,Cu)(In,Ga)Se2ultra‐thin solar cell, with 92% passivated rear interface area, is compared with a conventional nonpassivated counterpart. A thin MoSe2layer, for a quasi‐ohmic contact, is present in the two architectures at the contacts, despite the passivated device narrow line scheme. The devices present striking differences in charge carrier dynamics. Electrical and optoelectronic analysis combined with SCAPS modelling suggest a lower recombination rate for the passivated device, through a reduction on the rear surface recombination velocity and overall defects, comparing with the reference solar cell. The new architecture allows for a 2% efficiency improvement on a 640 nm ultra‐thin device, from 11% to 13%, stemming from an open circuit voltage increase of 108 mV.

Bandgap engineered, quantum-confined ultrathin Te layer for highly effective back surface field in Si/organic hybrid solar cells

The suppression of back surface carrier recombination is primary importance for efficient Si-based solar cells. It is usually achieved with back surface field (BSF) by introducing a highly doped layer on the rear surface, which require a high temperature doping processes and involves toxic gasses. Here, we report that a high power conversion efficiency of 13.1% with device area of 1cm2 has been achieved for planar Si-PEDOT:PSS hybrid solar cells by depositing a ultrathin tellurium (Te) layer between silicon and rear contact, without any high temperature process or further treatment. Current-voltage, electrochemical impedance spectroscopy, quasi-steady-state-photoconductance measurements are used to investigate the effect of Te BSF layer on the device performance. The insertion of Te BSF layer have successfully reduced charge carrier recombination at rear interface. In addition, it could reduce the contact resistance thanks to the favorable band alignment originated from quantum confinement effect, resulting in improved current density and fill factor. This is the very first demonstration that a quantum-confined material can be used as an effective passivating back surface field layer in Si-organic hybrid solar cells.

Cracked Film Lithography with CuGaOx Buffers for Bifacial CdTe Photovoltaics.

Bifacial CdTe solar cells with greater power density than the monofacial baselines are demonstrated by using a CuGaOx rear interface buffer that passivates while reducing sheet resistance and contact resistance. Inserting CuGaOx between the CdTe and Au increases mean power density from 18.0±0.5 to 19.8±0.4mWcm-2 for one sun front illumination. However, coupling CuGaOx with a transparent conductive oxide leads to an electrical barrier. Instead, CuGaOx is integrated with cracked film lithography (CFL)-patterned metal grids. CFL grid wires are spaced narrowly enough (≈10µm) to alleviate semiconductor resistance while retaining enough passivation and transmittance for a bifacial power gain: bifacial CuGaOx /CFL grids generate 19.1±0.6mWcm-2 for 1 sun front + 0.08 sun rear illumination and 20.0±0.6mWcm-2 at 1 sun front + 0.52 sun rear-the highest reported power density at field albedo conditions for a scaled polycrystalline absorber.

Detailed luminescence modelling in high-efficiency solar cells for precise calibration of spatially resolved characterisation methods: A bottom-up opto-electrical approach

In the scope of solar cell characterisation, spatially resolved imaging (SRI) methods (EL, PL and LBIC) have long been a standard procedure for valuable in-depth evaluation and extraction of various spatially resolved material properties, especially those related to the electrical behaviour. While this extraction can be straightforward in the case of laterally homogeneous devices, the situation is vastly different when the structural features are laterally varying, such as in the case of interdigitated back contact (IBC) solar cells. We show that in the case of laterally varying devices inherent device optical properties play a far more important role in determining the measured profile in this case and may indeed overshadow any underlying electrical effects. We therefore propose and validate a methodology that couples SRI characterisation with advanced bottom-up simulation of IBC solar cells. The method fully accounts for lateral device variability and allows for accurate extraction of the underlying electrical phenomena. We demonstrate the applicability of the method on state-of-the-art high-efficiency IBC solar cells, and explain the key factors, which could lead to misinterpretation of the results obtained solely by SRI measurements. • Interpretation of measured IBC electroluminescence profiles through opto-electrical simulation. • Decoupling of underlying optical and electrical phenomena. • Device optics overshadows recombination driven fluctuations of luminescence profiles. • Rear interface strongly influences the shape of the extracted luminescence profile. • Shape of the luminescence profile is highly dependent on imaging system’s aperture.

Rear interface engineering via a facile oxidation process of Mo back contact for highly efficient CZTSSe thin film solar cells

The kesterite-based Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells (TFSCs) are promising absorber material for next-generation TFSCs technology because they exhibit earth-abundant, non-toxic elements and favorable optoelectronic properties. However, the progress and device performance development in CZTSSe TFSCs were limited because of unstable rear interface characteristics near the absorber/molybdenum (Mo) interface, which causes large open-circuit voltage loss. In this study, we report the rear interface engineering of CZTSSe TFSCs to improve device performance by introducing an amorphous thin MoOx intermediate layer by a facile oxidation process. We observed that (i) an amorphous thin MoOx intermediate layer can effectively control the rear interface properties (i.e., inhibiting the formation of Mo(S,Se)2 interfacial layers and voids at CZTSSe/Mo interface) and (ii) the improved device performance in CZTSSe TFSCs with oxidation (w-oxidation) is attributed primarily to the dramatically decreased shunt conductance, formation of large-sized grains within CZTSSe absorber layer, and improved rear interface characteristics. This study presents a simple and low-temperature oxidation process for rear interface engineering of highly efficient kesterite CZTSSe-based TFSCs.