Constructing gradient structure to increase efficiency for carbon-based hole transport layer free all-inorganic perovskite solar cells using SCAPS-1D

Carbon-based all-inorganic perovskite solar cells (C-IPSCs) without hole transport layer (HTL) are of great interest because of their excellent stability and low production costs. In contrast to hybrid PSCs with HTLs, C-IPSCs have not yet attained great conversion efficiency. In this work, a new C-IPSC with gradient doping structure and gradient energy band structure using CsPbI3 as an absorber is proposed and numerically simulated by SCAPS-1D. The C-IPSC was optimized from various aspects including absorber layer thickness, doping gradient, doping concentration, defect, and energy band gradient. The optimal thickness of CsPbI3 is determined based on the optical absorption properties. Through a thorough analysis of the energy band structure, the intensity of the built-in electric field, and the recombination rate, it is found that the presence of the doping gradient introduces the built-in electric field, which promotes the movement of photogenerated carriers between the layers and significantly improves the efficiency of C-IPSCs. In order to address the issue of energy level mismatch, we propose to construct an energy band gradient. The presence of the energy band gradient improves the energy level matching of the device and provides paths for the movement of holes and electrons. In addition to the doping concentration, and defect density, we have chosen according to the optical performance and manufacturing level. Through a series of optimization, the C-IPSC with gradient structure has an efficiency of 21.15%. This study demonstrates that gradient doping structure and gradient energy band structure have great potential in future C-IPSCs with CsPbI3.