Origin of the high performance of perovskite solar cells with large grains

Due to excellent carrier transport characteristics, CH3NH3PbI3 film made of large single crystal grains is considered as a key to improve upon already remarkable perovskite solar cell (PSC) efficiency. We have used a simple and efficient solvent vapor annealing method to obtain CH3NH3PbI3 films with grain size over 1 μm. PSCs with different grain size films have been fabricated and verified the potential of large grains for improving solar cells performance. Moreover, the larger grain films have shown stronger light absorption ability and more photon-generated carriers under the same illumination. A detailed temperature-dependent PL study has indicated that it originates from larger radius and lower binding energy of donor-acceptor-pair (DAP) in larger grains, which makes the DAP is easily to be separated and difficult to be recombine.