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.

Electronic modulation on the inert basal plane of transition-metal dichalcogenides(TMDs) through vacancy defect excitation, although extremely challenging, is urgent for understanding the factors that impact the hydrogen evolution reaction (HER) catalytic activity. Here, ultrathin WS₂ nanosheets with precise quantitative single atomic S-vacancy on the inert basal plane were flexible prepared through hydrogen peroxide etching strategy. The as-synthesized single atomic S-vacancy defect WS₂ (SVD-WS₂) nanoflake with the activated basal plane exhibited an impressive overpotential of 137 mV at a current density of 10 mA·cm^-2 and a Tafel slope of 53.9 mV·dec^-1. Furthermore, anchoring on the defect graphene matrix, the assembled two-dimensional (2D) stacking heterojunction exhibits further enhanced HER catalytic activity (an overpotential of 108 mV vs. 10 mA·cm^-2 and a Tafel slope of 48.3 mV·dec^-1) and stability (~ 10% decline after 9, 000 cycles), which attributed to the electronic structure modulation from the synergetic interactions between SVD-WS₂ and defect graphene. Our finding provides a smart defects introduce strategy to trigger high-efficiency hydrogen evolution over WS₂ nanosheets and a general 2D heterojunctions fabricated inspiration based on strong interaction interface.