Challenge The Open Circuit Voltage Theory Limit Of MAPbBr₃ And MAPbI₃ Perovskite Solar Cells

With the increase in global energy demands and the deterioration in environmental issues,photovoltaic technology is often mentioned as a key to solve these issues.A myriad of photovoltaic materials and technologies were developed in the last few decades with the aim to fabricate solar cells with low cost,high power conversion efficiency,long-term lifetime,and environmental friendliness.Organic-inorganic halide perovskite materials have become a shining star in the photovoltaic field due to their unique properties,such as high absorption coefficient,optimal bandgap,and high defect tolerance.Perovskite solar cells have emerged as a competitive candidate for the new generation photovoltaic technology that is compatible with low-cost,low-temperature processing,flexible substrates,and large-area fabrication.Laboratory scale cells with the certified highest PCE of 22.7%have been achieved in just nine years.Driving further to industrial applications needs a scalable way to produce perovskite solar cells on large area.Carbon electrodes fabricated through printing process have been shown to be suitable for iodide perovskite solar cells.In our research,an open-circuit voltage(V_OC)of1.57 V and power conversion efficiency of 8.70%in planar MAPbBr₃ solar cells with carbon electrodes is obtained.The hole-transport-material-free MAPbBr₃ solar cells with the normal architecture show little hysteresis under simulated AM1.5 sunlight.Based on the analysis of the band alignment,it is found that the voltage loss across the interface between MAPbBr₃ and carbon is very small compared to the offset between the VBM of MAPbBr₃ and the work function of carbon.This finding implies either Fermi level pinning or highly doped region inside MAPbBr₃ layer exists.The band-edge electroluminescence spectra further support no back-transfer pathways of electrons across the MAPbBr₃/Ti O₂ interface.After an overwhelmingly fast increase,the power conversion efficiency of hybrid perovskite solar cells has been leveling at²2%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 anti-solvent,we optimize the one-step deposition method to fabricate MAPbI₃ perovskite films under the ambient air condition.With MAPbI₃ solar cells of a planar architecture,a record high V_OC of 1.18V is obtained under simulated AM1.5 sunlight.After systematic comparison on different electron transport layers?SnO₂ and Ti O₂?and FTO substrates of different roughness,the V_OC loss is proposed to be due to the poor luminescent property of the MAPbI₃ films.