Semi-transparent perovskite solar cells with a cross-linked hole transport layer

Semi-transparent perovskite solar cells (ST-PeSCs) have received great attention because of their excellent performance and promising application in areas such as tandem devices and building integrated photovoltaics (BIPVs). Critical across all these applications is achieving both high efficiency and stable photovoltaic performance of such devices. Realizing both of these properties simultaneously has not been possible using device architectures featuring the archetypal doped Spiro-OMeTAD as a hole transport layer (HTL). As such, in this work we explore the use of a solution-processed cross-linked HTL formed from N4,N4'-di(naphthalen-1-yl)-N4,N4'-bis (4-vinylphenyl)biphenyl-4,4'-diamine (VNPB) molecules as an alternative to the conventional Spiro-OMeTAD within an FTO/SnO2/C-60-SAM/Perovskite/HTL/MoOx/ultra-thin gold/MoOx ST-PeSC device architecture. Through an optimized multi-step thermal treatment process that maximizes charge extraction and reduces recombination from these devices, we can achieve ST-PeSCs that exhibit record power conversion efficiencies for Spiro-OMeTAD-free devices with average visible transmittance values between 10 and 30%. These devices exhibit comparable efficiencies to their Spiro-OMeTAD counterparts, with the additional benefit that the use of the poly-VNPB as the HTL material provides significant improvements in long-term device stability under both continuous illumination and high humidity conditions.