Bridging the inter-grain charge transport via organic semiconductors for high-performance thickness-insensitive perovskite solar cells

Abstract

The solution-processability of perovskite solar cells (PVSCs) reduces the production cost, but renders a multi-crystalline film with a large number of grain boundaries, which hinders the charge transport and induces defects. In this work, we have studied the potential of organic semiconductors for remedying the grain boundaries of perovskite films. Non-fullerene acceptors (NFAs) of different energy levels have been filled into the grain boundaries of perovskite films to form different energetic structures. It is unveiled that constructing a “flat-band” quantum well structure (FBQW, where the highest occupied molecular orbital and lowest unoccupied molecular orbital align with the valence band and conductance band, respectively), can effectively bridge the charge transport at the grain boundaries. As a result, the NFA, i.e., HFO-PCIC can obviously reduce the series resistance and enable the best device performance of over 21% based on MAPbI₃ solar cells. Moreover, constructing a FBQW at the grain boundary almost fully retains the device efficiency (20.7% for the best) with a perovskite thickness over 1500 nm, which is the best result among thick PVSCs. With the thickness-insensitive merit, the fabrication of perovskites will be more tolerant to the processing conditions toward practical application. Therefore, the FBQW proposed in this work can effectively remedy inter-grain charge transport for high device performance and should pave the way for thickness-insensitive perovskite solar cells for future commercialization of PVSCs.