Organic semiconductors are disordered molecular solids, and as a result, their internal charge generation dynamics, charge transport dynamics, and ultimately, the performance of the optoelectronic devices they constitute, are governed by energetic disorder. This is particularly pertinent for emerging photovoltaic technology where the extractable power is directly dependent on these dynamics. To ascertain how energetic disorder impacts charge generation, exciton transport, charge transport, and the performance of organic semiconductor devices, an accurate approach is first required to measure this critical parameter. In this work, it is shown that the static disorder of an organic semiconductor can be obtained from its photovoltaic external quantum efficiency spectrum at wavelengths near the absorption onset. A detailed methodology is presented, alongside a computational framework, for quantifying the static energetic disorder associated with singlet excitons. Moreover, the authors show that minimizing the limiting effects of optical interference is crucial for achieving high‐accuracy quantifications. Finally, transparent devices are employed to estimate the excitonic static disorder in several technologically relevant organic semiconductor donor–acceptor blends, including the high‐efficiency organic photovoltaic system PM6:Y6.

Due to their tailorable optical properties, organic semiconductors show considerable promise for use in indoor photovoltaics (IPVs), which present a sustainable route for powering ubiquitous “Internet‐of‐Things” devices in the coming decades. However, owing to their excitonic and energetically disordered nature, organic semiconductors generally display considerable sub‐gap absorption and relatively large non‐radiative losses in solar cells. To optimize organic semiconductor‐based photovoltaics, it is therefore vital to understand how energetic disorder and non‐radiative recombination limit the performance of these devices under indoor light sources. In this work, we explore how energetic disorder, sub‐optical gap absorption, and non‐radiative open‐circuit voltage losses detrimentally affect the upper performance limits of organic semiconductor‐based IPVs. Based on these considerations, we provide realistic upper estimates for the power conversion efficiency. Energetic disorder, inherently present in molecular semiconductors, is generally found to shift the optimal optical gap from 1.83 to ≈1.9 eV for devices operating under light emitting diode spectra. Finally, we also describe a methodology (accompanied by a computational tool with a graphical user interface) for predicting IPV performance under arbitrary illumination conditions. Using this methodology, we estimate the indoor power conversion efficiencies of several photovoltaic materials, including the state‐of‐the‐art systems PM6:Y6 and PM6:BTP‐eC9.

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