Minimized Energy Loss at the Buried Interface of p-i-n Perovskite Solar Cells via Accelerating Charge Transfer and Forming p-n Homojunction

The energy loss (E-loss) aroused by inefficient charge transfer and large energy level offset at the buried interface of p-i-n perovskite solar cells (PVSCs) limits their development. In this work, a BF4- anion-assisted molecular doping (AMD) strategy is first proposed to improve the charge transfer capability of hole transport layers (HTLs) and reduce the energy level offset at the buried interface of PVSCs. The AMD strategy improves the carrier mobility and density of poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) and poly[N,N '-bis(4-butilphenyl)-N,N '-bis(phenyl)-benzidine] (Poly-TPD) HTLs while lowering their Fermi levels. Meanwhile, BF4- anions regulate the crystallization and reduce donor-type iodine vacancies, resulting in the energetics transformation from n-type to p-type on the bottom surface of perovskite film. The faster charge transfer and formed p-n homojunction reduce charge recombination and E-loss at the HTL/perovskite buried interface. The PVSCs utilizing AMD treated PTAA and Poly-TPD as HTLs demonstrate a highest power conversion efficiency (PCE) of 24.26% and 22.65%, along with retaining 90.97% and 85.95% of the initial PCE after maximum power point tracking for 400 h. This work provides an effective way to minimize the E-loss at the buried interface of p-i-n PVSCs by accelerating charge transfer and forming p-n homojunctions.