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 of a mature photovoltaics 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 with other common hole conductors. For p-i-n structure, poly-triaryl(amine) is also routinely used as dopant-free hole transport layer, but problems in perovskite film growth, and 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 hole transport layers (BPT-1,2), aiming to solve the above-mentioned issues and allow upscale to the module level. By using BPT-1 and methylammonium-free perovskite, max. Power conversion efficiencies of 17.26% and 15.42% on a small area (0.09 cm2) and mini-module size (2.25 cm2), respectively, were obtained, with a better reproducibility than with poly-triaryl(amine). Moreover, BPT-1 was demonstrated to yield more stable devices compared with poly-triaryl(amine) under ISOS-D1, T1, and L1 accelerated life-test protocols, reaching maximum T90 values >1000 h on all tests.