Work function engineering to enhance open-circuit voltage in planar perovskite solar cells by g-C3N4 nanosheets

Enhancement of open-circuit voltage (Voc) is an effective way to improve power conversion efficiency (PCE) of the perovskite solar cells (PSCs). Theoretically, work function engineering of TiO2 electron transport layer can reduce both the loss of Voc and current hysteresis in PSCs. In this work, two-dimensional g-C3N4 nanosheets were adopted to modify the compact TiO2 layers in planar PSCs, which can finely tune the work function (WF) and further improve the energy level alignment at the interface to enhance the Voc and diminish the hysteresis. Meanwhile, the quality of perovskite films and charge transfer of the devices were improved by g-C3N4 nanosheets. Therefore, the PCE of the planar PSCs was champed to 19.55% without obvious hysteresis compared with the initial 15.81%, mainly owing to the remarkable improvement of VOC from 1.01 to 1.11 V. In addition, the stability of the devices was obviously improved. The results demonstrate an effective strategy of WF engineering to enhance Voc and diminish hysteresis phenomenon for improving the performance of PSCs.