Nitrogen-Doped Graphene Quantum Dots for 80% Photoluminescence Quantum Yield for Inorganic γ-CsPbI3 Perovskite Solar Cells with Efficiency beyond 16%

The insufficient utilization of sunlight has been a big obstacle preventing inorganic perovskite solar cells (PSCs) from achieving high power conversion efficiency (PCE). Herein, nitrogen-doped graphene quantum dots (N-GQDs) are developed to achieve a photoluminescence quantum yield (PLQY) as high as 80% to effectively convert harmful UV light into useful visible photons for improved solar cell efficiency. It is found that the N-GQD material is very stable against humidity and under high temperature stress. When it is deposited on the top of the -CsPbI3 PSCs, it serves as an energy-down-shift (EDS) layer to harvest light in the short wavelength range <350 nm that is normally detrimental to the perovskite. Compared with the reference cell without the N-GQDs, the optimized PSC exhibits an increased short circuit current density (J(SC)) of 19.15 mA cm(-2) from 18.67 mA cm(-2) and a PCE of 16.02% from 15.53%. Further examination of the EQE, PL and UV-vis absorption spectra confirms that the improvement in the device performance does indeed result from the N-GQDs. The present strategy paves the way for rational design to improve the performance of other novel photovoltaic devices.