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.

A PCDTBT:PC₇₁BM solar cell adopted by a ternary strategy with PDTSTPD achieves an overall PCE of 20.8% under indoor illumination.

A thick-film (∼200 nm) porphyrin-based P1:PC ₇₁ BM BHJ solar cell achieves an optimized PCE of 18.2%, under a 300 lux illumination of a 3000 K LED tube.

The “charge bridge” strategy is applied to organic photovoltaic devices, which dredges photocarrier trapping pathways by facilitating exciton–phonon decoupling. This benefit leads to simultaneous improvement of efficiency and photothermal stability.