Synergistic Trait of Dual Hole Transport Materials in High-Performance Inverted Tin Perovskite Solar Cells

Abstract PEDOT:PSS is widely employed as a hole transport layer (HTL) in inverted tin-based perovskite solar cells (TPSCs) owing to its high optical transmittance and excellent compatibility with tin perovskites (TPsks). However, its relatively low hole mobility and suboptimal energy-level alignment with TPsk limit device performance. In contrast, the inorganic semiconductor CuO exhibits superior hole mobility, low electron affinity, high transparency, and adjustable energy levels, but suffers from poor film morphology and inadequate interfacial compatibility with TPsks. A CuO/PEDOT:PSS dual-layer HTL (CuPE) was developed to synergistically combine the advantages of inorganic CuO and polymeric PEDOT:PSS while mitigating their respective drawbacks. TPSCs incorporating the CuPE-400 (when CuO was annealed at 400 °C) HTL achieved a champion power conversion efficiency (PCE) of 12.24%, which is significantly higher than those (8.72 and 8.65%, respectively) of devices employing either CuO-400 or PEDOT:PSS alone. CuPE-400-based devices retained 82% of their initial PCE after 1,584 h of storage in a glovebox, outperforming CuO-400 and PEDOT devices, which retained only 63 and 69% of their initial efficiencies, respectively. The excellent photovoltaic performance of CuPE-400 is attributed to its high hole mobility and low trap density, achieved through the partial interpenetration of CuO grains and PEDOT:PSS polymer chains (as revealed by X-ray photoelectron spectroscopy (XPS) depth profile analysis) to form a dense CuPE-400 film as well as a good-quality TPsk film, which was coated on CuPE-400. Notably, when CuO-250 was annealed at 250 °C, the CuPE-250-based cell still exhibited a PCE of 12.00%, which is very close to that of the device based on CuPE-400. These results demonstrate the potential of CuO-based HTLs for low-temperature processing.