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 (W_F) 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 V_OC from 1.01 to 1.11 V. In addition, the stability of the devices was obviously improved. The results demonstrate an effective strategy of W_F engineering to enhance Voc and diminish hysteresis phenomenon for improving the performance of PSCs.