Recent progress in enhancing built-in electric fields of perovskite solar cells via junction engineering

The performance of perovskite solar cells (PSCs) is primarily governed by the built-in electric field (BEF), which dictates photocarrier separation, drift-diffusion transport, and extraction pathways, thereby shaping critical device parameters such as open-circuit voltage and fill factor. This review highlights recent progress in junction engineering strategies for BEF enhancement. Homojunctions extend interfacial potential fields into the bulk through controlled doping and orientation modulation, thereby suppressing nonradiative recombination and improving carrier extraction. Gradient junctions introduce continuous compositional or bandgap tilts across the film thickness, enabling depth-extended electric fields and improved spatial continuity of charge transport. By contrast, 2D/3D heterojunctions exploit interfacial dipole formation, intrinsic polarization, and phase-penetration effects to amplify and homogenize the BEF, while simultaneously improving energy-level alignment and defect passivation. We systematically compare these strategies within a unified framework of BEF descriptors, magnitude, penetration depth, directionality, and spatial continuity. Special emphasis is placed on the potential for synergistic integration of multiple junction architectures and on the development of mild, process-compatible fabrication routes. Ultimately, optimizing the BEF provides a powerful lever for advancing power conversion efficiency, open-circuit voltage, and long-term operational stability in state-of-the-art PSCs, while avoiding the introduction of parasitic energy barriers.