A carbon-quantum-dot-hybridized NiOx hole-transport layer enables efficient and stable planar p–i–n perovskite solar cells with high open-circuit voltage

In recent years, the nickel oxide (NiOx)-based planar p–i–n perovskite solar cell (PSC) has progressed rapidly. Nevertheless, poor electrical properties of NiOx, unoptimized band alignment between NiOx and perovskites, as well as pervasive defects and unwanted chemical redox reactions at NiOx/perovskite interfaces have severely limited the device efficiency and stability. It is of particular interest to explore a facile approach to address these issues simultaneously. Herein, an effective carbon-quantum-dot-hybridized NiOx (CQD-hybridized NiOx) hole transport layer (HTL) is fabricated via hybridizing a kind of environmentally friendly CQD with NiOx. By virtue of the rich surface polar groups of CQDs, hybridization of such CQDs with NiOx can efficaciously upgrade the electrical properties of NiOx HTLs, thereby reducing ohmic loss and energy level offset at NiOx/perovskite interfaces. Meanwhile, the application of CQD-hybridized NiOx HTLs can boost the nucleation and growth of perovskite layers, thus suppressing the formation of interfacial defects/traps and reducing interface-mediated nonradiative recombination losses. Moreover, such CQD-hybridized NiOx HTL can also diminish redox reactions at the NiOx/perovskite interface, improving interface stability. Based on this CQD-hybridized NiOx HTL, a champion PCE of 20.53% with enhanced stability has been achieved. More strikingly, the optimized device delivers a Voc as high as 1.16 V, the highest Voc for CH3NH3PbI3 PSCs based on NiOx HTLs as far as we know. These results demonstrate that CQD-hybridized NiOx HTLs will be a promising candidate for efficient and stable planar p–i–n PSCs.