Carrier Transport Composites with Suppressed Glass-Transition for Stable Planar Perovskite Solar Cells

Poor stability is the most intractable factor undermining the confidence of academic and industry communities and impeding commercialization of perovskite solar cells (PSCs). The mostly used small molecule transport materials in PSCs such as spiro-OMeTAD always suffer undesired glass transition at relatively low temperature. Glass transition would induce phase transition, crystallization and further physical deformation of the film and formation of charge trap and short-circuited pathway that deteriorates power conversion efficiency (PCE) of PSCs. To achieve stable and efficient PSCs, we propose a robust small molecule and polymer hole transport composite (SMPHTC), wherein polymer is used as the skeleton, and small molecule materials as the crevice filler. In particular, we present a visualized method in the microscopic level to thoroughly understand the component spatial distribution of SMPHTC, their morphological evolution within the device under thermal stress. Planar n-i-p structure PSCs based on this composite showed PCE of 22.7% (reverse 23.3%, forward 22.0%) and stable output about 22.9%. Moreover, the obtained planar PSCs based on SMPHTC showed obviously improved stability, which preserved 90% of the original efficiency under 85 ○C for 1000 h and 92% of the highest stable output after tracking at maximum power point (MPP) for 560 h at room temperature. These results provide a deep understanding of low temperature glass transition suppression and suggest a general for efficient and stable PSCs.