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Pushing the Envelope: Achieving an Open‐Circuit Voltage of 1.18 V for Unalloyed MAPbI3 Perovskite Solar Cells of a Planar Architecture

After an overwhelmingly fast increase during the period from 2009 to 2016, the power conversion efficiency of hybrid perovskite solar cells levels at ≈22% during the past two years. Every small advance to theoretical limits of the photovoltaic metrics will significantly deepen the understanding of internal processes inside the perovskite solar cells. Here, by introducing chloroform as the antisolvent, the one‐step deposition method to fabricate methylammonium lead tri‐iodide (MAPbI3) perovskite films under ambient air condition is optimized. With MAPbI3 solar cells of a planar architecture, a record high Voc of 1.18 V is obtained under simulated AM1.5 sunlight. The achievement helps pure MAPbI3 to reestablish its potential as a model compound for research in hybrid perovskite solar cells. After systematic comparison on different electron transport layers (SnO2 and TiO2) and fluorine doped tin oxide (FTO) substrates of different roughness for photon trapping inside MAPbI3 solar cells, the remaining 0.14 V Voc loss is elucidated to be due to the poor luminescent property of the MAPbI3 films.