The Thermodynamic Limit of Indoor Photovoltaics Based on Energetically-Disordered Molecular Semiconductors

TL;DR

This paper investigates the fundamental limits of indoor organic photovoltaics, focusing on how energetic disorder and non-radiative losses constrain efficiency, and provides a computational tool for performance prediction under various lighting conditions.

Contribution

It introduces a methodology and computational tool to predict indoor photovoltaic performance considering energetic disorder and non-radiative effects, and identifies optimal optical gaps for device efficiency.

Findings

Optimal optical gap shifted from 1.83 eV to ~1.9 eV under LED spectra.

Energetic disorder limits maximum efficiency of organic IPVs.

State-of-the-art systems PM6:Y6 and PM6:BTP-eC9 are evaluated using the new methodology.

Abstract

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 nonradiative 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. The energetic disorder, inherently present in molecular semiconductors, is generally found to shift the optimal optical gap from 1.83 eV to ~1.9 eV for devices operating under LED 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 PCEs of several photovoltaic materials, including the state-of-the-art systems PM6:Y6 and PM6:BTP-eC9.