Abstract
In CH3NH3PbI3-based high efficiency perovskite solar cells (PSCs), tiny amount of PbI2 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 PbI2. This was mainly due to the inferior morphology of pure perovskite film without PbI2, inevitably produced when the remaining PbI2 forced to be converted to perovskite, so advantages of pure perovskite photoactive layer without PbI2 impurity have been overlooked. In this work, we designed a printing-based two-step process, which could not only generate pure perovskite crystal without PbI2, 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 PbI2. 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 PbI2 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.
Highlights
In CH3NH3PbI3-based high efficiency perovskite solar cells (PSCs), tiny amount of PbI2 impurity was often found with the perovskite crystal
This process was further applicable to prepare mixed phase pure perovskite crystal without PbI2 impurity, and we showed that partial replacement of MAPbI3 and (MA) cation of pure MAPbI3 with FA cation using the printing process, not degrading the high crystallinity without PbI2 impurity and forming α-phase (MA)x(FA)1−xPbI3, was beneficial to broadening the absorption wavelength range with the additional increase of the carrier life time and the reduction of charge recombination, proved by UV-Vis, time-resolved photoluminescence (TRPL), and transient photovoltage (TPV), respectively
Because a shear stress applied to the solution across the whole depth between substrate and silicone film is much more effective than that between a substrate and an air surface, which decreases from the substrate to be zero at the air interface[23,24,25], it is expected that MAI during this process can be more efficiently diffused to PbI2 in mp TiO2 template than that during the conventional spin-casting process
Summary
In CH3NH3PbI3-based high efficiency perovskite solar cells (PSCs), tiny amount of PbI2 impurity was often found with the perovskite crystal. 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. This process was further applicable to prepare mixed phase pure perovskite crystal without PbI2 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. (d) Au electrode deposition on top of the hole transport layer (Spiro-MeOTAD), casted on perovskite layer, after removing the gas-permeable stamp
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