From 33% to 57%-An elevated potential of efficiency limit for indoor photovoltaics

The limiting power conversion efficiency (PCE) defines the theoretical maximum efficiency of photovoltaic devices. The classic Shockley-Queisser method has predicted 33% for a single p-n junction solar cell under AM1.5G illumination, but those for alternative photovoltaic materials and under other illumination conditions are not well-established. The emergence of indoor photovoltaics (IPVs) generates considerable interest in this regard. Here, we explore how thin-film photovoltaic materials with different bandgaps, absorption properties, and thicknesses, perform as IPV devices. We show a material bandgap of 1.82-1.96 eV to allow a limiting 51-57% PCE for a single-junction device under various indoor illuminations. In addition, typical organic photovoltaic thin films of ∼100 nm only give limiting PCEs of merely ∼28%, but >40% for a 200-250 nm thick device making use of the second thickness peak. We also present the limiting device parameters under different illuminance, serving as a comprehensive guide for emergent IPV development. The limiting PCE and the optimal V_oc depend only weakly on the indoor light source and the domestic illuminance (100-1000 lx). In contrast, the limiting J_sc increases linearly with the illuminance (∼11-13 μA cm^-2/100 lx). Our study offers an explicit reference for evaluating the quality of an IPV device and a guideline for future material selection for efficient IPVs.