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 MAPbI₃ 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 MAPbI₃ 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 MAPbI₃ 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.