Easily Accessible Polymer Additives For Tuning The Crystal-growth Of Perovskite Thin-films For Highly Efficient Solar Cells

Organic-inorganic hybrid perovskite has attracted considerable attention due to its unique properties. One of the main challenges encountered in perovskite thin-films fabrication is the control of crystallization process and its impact on film quality. There is a simple and effective method to solve the problem, which is the introduction of additive. In this study, an easily-accessible and environment friendly polymer additive polyethylenimine(PEI) is utilized to tune the morphology of CH3NH3PbI3-xClx thin-films. Specifically, we introduced PEI into the perovskite precursor solution to tune the crystal-growth of CH3NH3PbI3-xClx. And we also investigated the effect of perovskite crystallization based on the different amount of PEI additive. After the addition of PEI, the crystallinity and morphology of perovskite thin-films have been changed, which were characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD), alternating current impedance spectroscopy(ACIS), steady-state and time-resolved photoluminescence(PL). We found that the moderate amount of PEI has positive effects on the uniform crystal-growth of perovskite, which enlarges the individual grain size, reduces the voids and improves the smoothness of the perovskite thin-films during the annealing process. The properties of perovskite crystals have profound influence on device performance. The performance of CH3NH3PbI3-xClx-based perovskite solar cells with 1.00 wt% of PEI achieved a summit PCE of 14.07%, which demonstrated a 26% increase compared with the PCE of 11.07% of the control device. These results demonstrate that PEI is an effective additive to improve the quality of perovskite thin-films and has great potential to be a new candidate as an easily-accessible additive for mass production of Pero-SCs.