Stable Methylammonium‐Free p‐i‐n Perovskite Solar Cells and Mini‐Modules with Phenothiazine Dimers as Hole Transporting Materials

Abstract During the last decade, perovskite solar technologies underwent an impressive development, with power conversion efficiencies reaching 25.5% for single junction devices, and 29.8% for Silicon-Perovskite tandem configurations. Even though research mainly focused on improving the efficiency of perovskite photovoltaics (PV), stability and scalability remain fundamental aspects for a mature PV technology. For n-i-p structure perovskite solar cells, using poly-triaryl(amine) (PTAA) as hole transport layer (HTL) allowed to achieve marked improvements in device stability compared to other common hole conductors. For p-i-n structure, PTAA is also routinely used as dopant-free HTL, but problems in perovskite films growth, as well as its limited resistance to stress and imperfect batch-to-batch reproducibility, hamper its use for device upscaling. Following previous computational investigations, in this work we report the synthesis of two small-molecule organic HTLs (BPT-1,2), aiming to solve the above-mentioned issues and allow upscale to module level. By using BPT-1 and methylammonium-free perovskite max. PCEs of 17.26% and 15.42% on small area (0.09 cm2) and mini-module size (2.25 cm2), respectively, were obtained, with a better reproducibility than with PTAA. Moreover, BPT-1 was demonstrated to yield more stable devices compared to PTAA under ISOS-D1, T1 and L1 accelerated life test protocols, reaching maximum T90 values >1000 hours on all tests.