Validating and comparing reported indoor photovoltaic performance

Indoor photovoltaics (PVs) have garnered significant attention in recent years as promising power sources for wireless Internet-of-Things devices. However, the use of unstandardised testing practices makes it difficult to compare reported performance metrics. Discrepancies between experimental apparatus and methodologies can arise in a number of ways, including non-standard light sources with varying spectral irradiance (irrespective of the colour temperature or the colour-rendering index), spectral deviations induced during light attenuation, spatial non-uniformities, and temporal instability and an angular distribution of the light source. Unstandardised practices lead to variations in the spectral shape and light power impinging on a PV device, resulting in variations in the output current and power conversion efficiency. In this contribution, we explore the imprecision that arises when comparing previously reported unstandardised measurements. By quantifying and combining different sources of measurement imprecision, retrospective thermodynamic analyses are used to validate reported measurements for a variety of established and next-generation PV systems. These retrospective analyses allow each measurement to be categorised as either thermodynamically valid, plausible, or implausible. Ultimately, our investigations clarify the current upper bounds of state-of-the-art indoor PV performance, with the maximum validated power conversion efficiencies of the indoor PVs we consider being 40.3%, 29.2%, and 40.9% for perovskite, organic, and inorganic semiconductor-based systems, respectively.