p–n heterojunction perovskite solar cell with bilateral Ohmic contacts

The tunability of the carrier/conduction polarity of halide perovskite via intrinsic defect self-doping makes it possible to implement a simple p–n heterojunction perovskite solar cell. Here, approaching 16% efficient prototype device of the p-type spiro-MeOTAD/n-type MAPbI3 heterojunction perovskite solar cell is demonstrated via synergetic energy band and interface engineering. The n-type perovskite is enabled by self-doping associated with excess PbI2, avoiding a redundant electron transport layer, while the oxygen-induced p-type extrinsic doping (oxidation) of spiro-MeOTAD ensures its high hole conductivity and Ohmic contact with Au back electrode. Furthermore, ITO's effective work function is reduced by the polar molecular modification layer to ensure its Ohmic contact with perovskite. Also, the functional groups of this modification layer effectively passivate the front interface defects, contributing to the enhanced device performance observed. This work highlights the great potential of facile energy band and interface engineering for efficient and simple-structured perovskite solar cells.