One-step-spin-coating route for homogeneous perovskite/pyrrole-C60 fullerene bulk heterojunction for high performance solar cells

To overcome obstacle of unbalanced hole and electron diffusion behavior in perovskites, a novel type of rationally designed bulk-heterojunction with C60-fullerene electron extraction material coupled with perovskite is for the first time reported. A facile strategy is developed for pyrrole to modify C60 to realize co-soluble of C60 and perovskites, achieving co-deposition of perovskite/pyrrole-fullerene bulk-heterojunction film via a one-step-spin-coating process. The unique perovskite/pyrrole-fullerene bulk-heterojunction exhibits increased mobility, quenched fluorescence intensity, decreased electron lifetime, large recombination resistance and reduced trap density of states, greatly enhancing charge extraction and transfer ability, thus boosting photoelectric conversion efficiency of solar cells. Introducing pyrrole-fullerene can effectively reduce grain boundaries and electron trap density to suppress electron-hole recombination. The enlarged interfacial area between pyrrole-fullerene and perovskite is essential for facilitating extraction of more free electrons from perovskite to fullerene electron acceptor, resulting in a balance of charge extraction and transport. A maximum power conversion efficiency of 18.9% with virtually no hysteresis for the bulk-heterojunction based perovskite solar cells with an optimized concentration of bulk-heterojunction can be obtained. The present strategy for high-performance bulk-heterojunction perovskite solar cells can be potential for industrial photovoltaic applications for its facile and low-cost process route.