Back interface management by multifunctional composite carbon nanospheres electrode for efficient and stable HTL-free carbon-based perovskite solar cells

The fabrication of a carbon electrode with high hole extraction and simultaneous the function of improving back interface properties is a critical and efficient strategy to enhance the performance of carbon-based perovskite solar cells (C–PSCs) free of hole transport layer (HTL). Herein, a compound of MoS2 and MoP in situ composite N, P co-doped carbon nanospheres (MoS2–MoP/NPC) is constructed as an efficient carbon electrode for HTL-free PSCs. The excellent p-type characteristic of MoS2, the high conductivity of MoP and the co-doping of N, P heteroatoms endow the composite carbon nanospheres with high hole mobility and conductivity and a down-shifted work function, which significantly promotes the extraction and transportation of holes and decreases energy loss. Meanwhile, the N, P and S components of the MoS2–MoP/NPC nanospheres exert a passivation effect on the surface free positive ions defects of the perovskite film, resulting in a remarkable reduction in non-radiative recombination at back interface. As a result, the HTL-free CsPbBr3 PSCs without any encapsulation based on MoS2–MoP/NPC electrode achieve a champion power conversion efficiency of 10.13% with a significant open-circuit voltage of 1.638 V and excellent long-term stability after storage at 85% RH, 85 °C in air for 30 days. This work provides a new perspective for designing multifunctional carbon electrode materials that holistically optimize the back interface to improve the efficiency and stability of HTL-free C–PSCs.