Investigation into the Advantages of Pure Perovskite Film without PbI for High Performance Solar Cell.

In CHNHPbI-based high efficiency perovskite solar cells (PSCs), tiny amount of PbI impurity was often found with the perovskite crystal. However, for two-step solution process-based perovskite films, most of findings have been based on the films having different morphologies between with and without PbI. This was mainly due to the inferior morphology of pure perovskite film without PbI, inevitably produced when the remaining PbI forced to be converted to perovskite, so advantages of pure perovskite photoactive layer without PbI impurity have been overlooked. In this work, we designed a printing-based two-step process, which could not only generate pure perovskite crystal without PbI, but also provide uniform and full surface coverage perovskite film, of which nanoscale morphology was comparable to that prepared by conventional two-step solution process having residual PbI. Our results showed that, in two-step solution process-based PSC, pure perovskite had better photon absorption and longer carrier lifetime, leading to superior photocurrent generation with higher power conversion efficiency. Furthermore, this process was further applicable to prepare mixed phase pure perovskite crystal without PbI impurity, and we showed that the additional merits such as extended absorption to longer wavelength, increased carrier lifetime and reduced carrier recombination could be secured.