Simulated tin perovskite solar cell reaches 26.91% efficiency

A numerical study of a lead-free perovskite solar cell reports a theoretical power-conversion efficiency of 26.91% after jointly optimizing its absorber, transport layer, interfaces, electrical losses, operating temperature and rear contact. The modeled device uses a 600 nm FASnI3 absorber, a 200 nm Cs2SnI6 interfacial layer, a ZnOS electron-transport layer and a metal back contact with a work function of 5.2 eV. Under the selected conditions, the simulated cell produces an open-circuit voltage of 1.09 V, a short-circuit current density of 29.40 mA cm−2 and a fill factor of 83.85%. These results represent an optimized SCAPS-1D prediction rather than a measured efficiency from a fabricated device, and the authors caution that several important losses and degradation mechanisms are absent from the model.

FASnI3 is a tin-based metal-halide perovskite being investigated as an alternative to lead-containing absorbers because of the toxicity concerns associated with lead. The material has an optical band gap of about 1.41 eV, while Cs2SnI6 has a slightly wider gap of 1.48 eV. In the proposed stack, FASnI3 serves as the principal light-absorbing layer, while Cs2SnI6 is treated as both a photoactive secondary layer and an interfacial passivation layer. The authors propose that it may suppress recombination and limit interactions between the absorber and rear electrode, but the environmental-protection and stability benefits remain theoretical because the simulation does not model moisture, oxygen, ion migration or long-term chemical degradation.

The calculations were performed with SCAPS-1D version 3.3.10 using a one-dimensional drift-diffusion framework. This software numerically solves the coupled Poisson and electron and hole continuity equations to calculate carrier generation, transport, recombination, current-voltage behavior, external quantum efficiency and band diagrams. The devices were evaluated at 300 K under standard AM 1.5G illumination, with FTO as the front transparent contact and a flat-band condition at the rear. Most material parameters were taken from literature, including band gaps, carrier mobilities, effective densities of states, doping and defect concentrations. Because these inputs vary among publications, the comparison of electron-transport materials is better interpreted as a device-level screening exercise than as a definitive ranking of intrinsic material performance.

ZnOS produced the strongest initial result among nine candidate electron-transport layers, which also included C60, CeO2, IGZO, PCBM, SnO2, TiO2, ZnO and WS2. Its simulated power-conversion efficiency was approximately 22.99%, compared with about 18.49% for WS2 and 17.39% for ZnO. The ZnOS device delivered an open-circuit voltage of 1.02 V and a short-circuit current density of 27.47 mA cm−2, together with the highest fill factor in the comparison. Band alignment, mobility and interfacial quality were identified as the main explanations for the differences. The model associated ZnOS with a favorable conduction-band offset, effective electron extraction, limited hole backflow and comparatively low interfacial recombination, although these attributes were not tested experimentally.

The unoptimized FASnI3/Cs2SnI6 structure initially achieved a simulated efficiency of 16.87%, with an open-circuit voltage of 1.00 V, a short-circuit current density of 24.46 mA cm−2 and a fill factor of 68.81%. Increasing the FASnI3 thickness from 100 to 600 nm raised the modeled efficiency from 14.93% to 24.32%, the open-circuit voltage from 0.95 to 1.03 V and the short-circuit current density from 19.79 to 28.52 mA cm−2. The gain in current largely flattened beyond approximately 400–500 nm, indicating that recombination and transport constraints increasingly offset the benefit of additional absorbing material. Varying the Cs2SnI6 layer from 10 to 200 nm raised efficiency from about 17.0% to 18.6%, with little change in current density, supporting its proposed role as an interfacial transport and passivation layer rather than the main optical absorber.

Defect density was among the most influential modeled variables. At a bulk defect density of 1 × 10^13 cm−3 in FASnI3, the simulated device reached an efficiency of 23.91%, an open-circuit voltage of 1.03 V, a current density of 27.51 mA cm−2 and a fill factor of 83.98%. Increasing the defect density to 1 × 10^19 cm−3 lowered the corresponding values to 10.49%, 0.73 V, 21.43 mA cm−2 and 66.20%. The model attributes this decline to trap-assisted Shockley-Read-Hall recombination, shorter carrier lifetimes and reduced collection of photogenerated charge. Interface defects at the ZnOS/FASnI3 contact caused a smaller efficiency decrease, from roughly 23.29% to 22.94% over the tested range, whereas efficiency at the FASnI3/Cs2SnI6 interface remained near 22.99% as its defect density rose from 10^13 to 10^19 cm−3.

Electrical parasitics proved especially damaging to fill factor. Raising the area-specific series resistance from 1 to 50 Ω cm2 reduced simulated efficiency from 22.35% to 5.08%, lowered the fill factor from 79.45% to 25.26% and reduced current density from 27.45 to 19.62 mA cm−2, while leaving the open-circuit voltage at 1.02 V. Conversely, increasing shunt resistance from 100 to 5,000 Ω cm2 raised efficiency from 13.94% to 22.82% and the fill factor from 53.88% to 81.09%, after which the response approached saturation. The modeled optimum therefore required very low series resistance and very high shunt resistance. Raising the back-contact work function from 4.5 to about 5.1 eV also improved voltage, fill factor and efficiency, with little effect on current density, before the response reached a plateau.

Temperature was modeled across 275–450 K. As temperature increased, current density changed little, but open-circuit voltage fell from 1.06 to 0.75 V, the fill factor declined from 82.5% to 74.62% and efficiency dropped from 24.2% to 15.35%. The authors associate this behavior with temperature-dependent changes in defect activation, carrier diffusion, resistive losses and carrier-carrier interactions. The modeled maximum occurred at 275 K, but this steady-state electrical result cannot establish operational stability or longevity. The authors state that the model omits moisture ingress, oxygen-driven oxidation of Sn2+ to Sn4+, ion migration, phase transitions, interfacial interdiffusion and light-induced degradation, all of which would require controlled aging and light-soaking experiments to assess.

The final optimized configuration, FTO/ZnOS/FASnI3/Cs2SnI6/back contact, incorporated low bulk and interface defect densities, a 600 nm absorber, a 200 nm Cs2SnI6 layer, a Cs2SnI6 acceptor concentration of 10^19 cm−3, a shunt resistance of 5,000 Ω cm2, a series resistance of 1 Ω cm2 and a 5.2 eV rear-contact work function. Its simulated external quantum efficiency extended from 300 to 900 nm, and its illuminated impedance spectrum showed a larger semicircle than the initial device, which the model interprets as higher interfacial recombination resistance. Nevertheless, SCAPS-1D assumes homogeneous layers and idealized transport, does not capture grain boundaries, pinholes, lateral nonuniformity, hysteresis, chemical reactions, parasitic optical absorption or three-dimensional transport, and can model only seven layers. The 26.91% result should therefore be treated as an upper-bound computational outcome for the selected assumptions, not as evidence that a working 26.91%-efficient solar cell has been built. Experimental fabrication, material synthesis, controlled environmental exposure, thermal aging, light soaking and maximum-power-point tracking would be needed to determine whether the proposed interface can deliver the modeled electrical benefits in practice.

Subject of Research: Numerical optimization of a lead-free FASnI3/Cs2SnI6 perovskite solar cell

Article Title: Cs 2 SnI 6 -Mediated interfacial engineering for high-performance FASnI 3 perovskite solar cells: A SCAPS-1D study

Article References: Ullah, S., Shah, A. U. I., Khan, F., & Meyer, E. L. (2026). Cs2SnI6-Mediated interfacial engineering for high-performance FASnI3 perovskite solar cells: A SCAPS-1D study. Results in Engineering, 32, Article 113592. https://doi.org/10.1016/j.rineng.2026.113592

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113592

Keywords: perovskite solar cells, tin perovskite, FASnI3, Cs2SnI6, SCAPS-1D, lead-free photovoltaics, interfacial engineering, defect passivation, band alignment, solar-cell simulation, Mediated, interfacial