Undoped Hole Transport Layer Toward Efficient and Stable Inorganic Perovskite Solar Cells

Numerous strategies have been practiced to improve the power conversion efficiency of CsPbI2Br-based perovskite solar cells (PSCs), which definitely makes efficiency gradually approach the theoretical efficiency limit. However, sufficient device stability is still in urgent demand for commercialization, pushing to overcome some instability sources induced by hygroscopicity of spiro-OMeTAD and residual strain of perovskite layer. To address these issues, p-type semiconductor of PCPDTBT is used to replace spiro-OMeTAD, enabling dual functions of hole transport and strain regulation. On the one hand, undoped PCPDTBT performs excellent hole extraction and transport, while avoiding the perovskite degradation caused by the hygroscopicity of common additives. On the other hand, PCPDTBT assisted by a thermally spin-coating method compensates for the thermally-induced residual strain in perovskite layer owing to its high thermal expansion coefficient. Consequently, CsPbI2Br-based PSCs with PCPDTBT layer achieve improved efficiency of 16.5% as well as enhanced stability. This study provides a simple and facile strategy to achieve efficient and stable CsPbI2Br-based PSCs.