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 the commercialization of perovskite solar cells (PSCs). The mostly used small molecule transport materials in PSCs such as spiro-OMeTAD always suffer from undesired glass transition at relatively low temperatures. Glass transition would induce phase transition, crystallization and further physical deformation of the film and formation of a charge trap and short-circuited pathway that deteriorates the 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 a polymer is used as the skeleton, and small molecule materials as the crevice filler. In particular, we present a visualized method at the microscopic level to thoroughly understand the component spatial distribution of the SMPHTC, and its morphological evolution within the devices under thermal stress. Planar n-i-p structure PSCs based on this composite showed a PCE of 22.7% (reverse 23.3% and forward 22.0%) and a stable output of about 22.9%. Moreover, the obtained planar PSCs based on the SMPHTC showed obviously improved stability and preserved 90% of the original efficiency below 85 degrees C for 1000 h and 92% of the highest stabilized power output (SPO) after tracking for 560 h at room temperature without cooling. These results provide a deep understanding of low temperature glass transition suppression and suggest a general method for efficient and stable PSCs.