Asymmetric Doping–Driven Internal Field Engineering in p–n Homojunctions for Efficient Perovskite Solar Cells

Efficient perovskite solar cells (PSCs) require precisely engineered internal electric fields to promote charge separation and suppress recombination. Although p–n homojunctions offer an intrinsic route to generate such fields, their implementation has been hindered by interfacial degradation and the processing constraints of conventional multilayer fabrication. In this work, interfacial‐defect‐free MAPbI 3 p–n homojunctions are constructed by integrating stoichiometry‐controlled self‐doping with solvent‐assisted hot‐pressing transfer (HPT). This approach enables independent modulation of the doping polarity in the top and bottom MAPbI 3 layers, resulting in structurally coherent bilayers with reinforced built‐in fields. Experimental characterization combined with drift–diffusion simulations shows that device performance is optimized when the top MAPbI 3 layer is strongly p‐doped and the bottom layer is moderately n‐doped, a doping configuration that strengthens the internal field, enhances carrier separation, and reduces hysteresis. Under these optimized conditions, the p–n homojunction architecture delivers a relative improvement in power conversion efficiency of approximately 22% compared to the intrinsic bilayer device. These findings establish a unified experimental–theoretical framework for HPT‐based homojunction PSCs and highlight controlled doping asymmetry as a central design principle for high‐efficiency perovskite photovoltaics.