Efficient ambient-air-stable HTM-free carbon-based perovskite solar cells with hybrid 2D-3D lead halide photoabsorbers

Hole transport material (HTM)-free carbon-based perovskite solar cells (C-PSCs) have shown much promise because of their excellent stability and low cost. However, the most commonly used three-dimensional (3D) MAPbI(3) photoabsorber is ambient-unstable and incompatible with the low-cost mass-production of C-PSCs. Considering the proven operational stability of two-dimensional (2D) perovskites, we herein attempt to use a series of new 2D-3D hybrid (EA)(2)(MA)(n-1)PbnI3n+1 perovskites in C-PSCs. We find that the fabricated (EA)(2)(MA)(n-1)PbnI3n+1 films (n = 20, 10, and 6) exhibit extremely improved ambient and photo-stability under 60 day-ambient conditions. The HTM-free C-PSCs with a structure of ITO/C-60/(EA)(2)(MA)(n-1)PbnI3n+1/C retain outstanding power conversion efficiency over 11.88%. Particularly, by tuning the stoichiometry of (EA)(2)(MA)(n-1)PbnI3n+1 to n = 6, the n(6)-2D device maintains a long-term stability of 93% under ambient conditions after 2160 hours, a thermal stability of 80% after heating at 80 degrees C over 100 hours, and a photo-stability of 92% under continuous 1 sun illumination over 300 hours, which are apparently superior to those of the MAPbI(3) device (i.e. ambient stability of 73%; thermal stability of 9%; photo-stability of 67% after 83 hours). To the best of our knowledge, our fabricated C-PSC with the 2D-3D halide photoabsorber exhibits the best ambient-air-stable performance among all low-temperature carbon electrode-based PSCs reported so far.