Sustainable optoelectronic architecture of polymer-based HTLs for high-performance CsSnI₂Br perovskite solar cells

Lead-free cesium tin iodide bromide (CsSnI₂Br) perovskite solar cells (PSCs) have emerged as sustainable candidates for next-generation photovoltaics, combining a suitable bandgap with environmental safety. Yet, their performance is hindered by interfacial recombination and the spontaneous oxidation of Sn²⁺ to Sn⁴⁺, which degrades carrier mobility and device stability. While chemical stabilization approaches address this oxidation experimentally, its influence on electronic processes can be systematically evaluated through numerical modeling. In this work, the SCAPS-1D simulator was employed to investigate the optoelectronic response of CsSnI₂Br PSCs integrated with different polymer-based hole transport layers (HTLs), namely PEDOT:PSS, Spiro-OMeTAD, PTAA, Poly-TPD, P3HT, and PANI. Key parameters, including HTL thickness, doping concentration, and defect density—were tuned to analyze charge extraction efficiency and minimize interfacial recombination losses. Among the tested configurations, PEDOT:PSS yielded the highest simulated power conversion efficiency of approximately 21.4%, attributed to its favorable band alignment and enhanced hole mobility. Optimal performance was obtained for an absorber thickness of 0.8 µm and HTL thickness in the 50–80 nm range, provided that bulk and interfacial defect densities were below 5 × 10¹⁴ and 1 × 10¹⁵ cm⁻³, respectively. Additional improvements were achieved with TiO₂ ETL doping levels of 10¹⁷–10¹⁸ cm⁻³ and a back-contact work function near 4.8 eV. The device maintained robust output up to 320 K, demonstrating stable charge transport and reduced trap-mediated losses. These results provide valuable theoretical insights for optimizing HTL selection and interface engineering in efficient, lead-free perovskite photovoltaics.