Organic photovoltaics (OPVs) have shown great potential as new generation energy sources because they possess many unique properties, including mechanical flexibility, light weight, semitransparency and low fabrication cost. In particular, OPV devices exhibit high power conversion efficiencies under indoor and low-level lighting conditions. Therefore, they can function as promising energy sources in low-light or cloudy environments for many applications, including internet of things, wearable electronics and sensors. In this article, we review recent progress in OPV devices for these special applications. We start with introduction to the fundamental principles of OPVs. Then, we review the preparation and design principles of the photoactive layers for indoor applications. We also highlight the importance of interlayers in high-performance photovoltaic devices under indoor and/or low-level lighting illumination conditions. Recent efforts to improve the efficiencies of the indoor OPV devices using plasmonic nanostructures are also summarized. Finally, we examine the progress in large-area devices and modules for indoor and/or low-level lighting applications. We believe the rapid progress in indoor OPV cells and modules can trigger the development of low-cost, highly efficient OPV products for indoor applications in the near future.