Exploring photocurrent gradients inside tilted radial junctions via geometric tuning under back-reflection of the Al substrate

Radial junction (RJ) architectures, fabricated on metal foils, enable flexible thin-film solar cells with high performance and superior mechanical stability. In such configurations, the core silicon nanowires (SiNWs), grown via the vapor-liquid-solid (VLS) process, are randomly oriented with different tilting angles relative to the substrate. Although light absorption in vertically aligned RJ arrays has been explored, the photocurrent generation gradient and light-harvesting behaviors in tilted RJ arrays remain poorly understood, especially under back-reflection from metal-foil substrates, which critically impact filling factor (FF) and voltage output. In this work, finite-element simulations have been performed for a systematic comparison of the light absorption and photocurrent distribution inside tilted RJs across varying tilting angles on Al and glass substrates, respectively, for different wavelength ranges and RJ segments (face-up front-halves and face-down back-halves). Although tilting angles negligibly affect the overall EQEs, they markedly break the light absorption symmetry inside tilted RJs, thus leading to a larger photocurrent gradient. While the back-reflection of Al substrates can suppress the photocurrent gradient for a more uniform generation by redistributing internal light harvesting via geometrically tailoring RJs. These results establish a foundation for the simplified fabrication of high-efficiency flexible RJ-structured thin-film solar cells.