Optimization of GaInP Absorber Design for Indoor Photovoltaic Conversion Efficiency above 40%

Indoor photovoltaics (IPV) is a key technology for powering low-energy electronics, particularly Internet of Things devices, where wired power or frequent battery replacements are impractical. IPV cells convert artificial indoor light into electrical energy, enabling autonomous operation in environments with continuous illumination. While various tunable bandgap technologies have achieved high conversion efficiencies, many lack long-term stability. In contrast, III-V compound photovoltaics meet industrial standards, offering 25þ years of durability. Among them, Ga0.51In0.49P (GaInP) exhibits an almost optimal bandgap of 1.9 eV for indoor applications, achieving very high efficiencies even at 100 lx. This study investigates charge carrier dynamics in low-injection regimes for both p- and n-type GaInP. The effective radiative recombination coefficient (Brad,eff) and effective radiative efficiency were determined to measure non-radiative charge carrier lifetimes. The results explain the performance differences between homojunction (mainly p-type absorber) and rear-heterojunction (only n-type absorber) photovoltaic cells. The n-type material exhibits minority charge carrier lifetimes two orders of magnitude higher under low-light conditions due to a significant reduction in non-radiative recombination. Consequently, the rear-heterojunction design maintained higher excess charge carrier densities, leading to superior fill factor and open-circuit voltage compared to the homojunction. These findings highlight the potential of n-type GaInP for high-efficiency indoor energy harvesting.