Selenium-Based Indoor Photovoltaics Featuring PEDOT Hole Transport Layers in a Regular Device Configuration

Selenium (Se), the first material used in solid-state photovoltaics, has recently gained renewed attention as a wide-band-gap absorber for indoor photovoltaic (IPV) applications. In this study, thermally evaporated trigonal Se thin films were integrated into regular planar devices incorporating a top-side hole transport layer (HTL) composed solely of water-free poly(3,4-ethylenedioxythiophene) (PEDOT) dispersed in toluene. This represents the first application of PEDOT as a single HTL in a Se-based architecture without additional interfacial layers. The effects of the annealing temperature, annealing sequence, HTL incorporation, and Se thickness on structural and optoelectronic properties were systematically investigated. Postannealing at 200 °C induced crystallization with a preferred (100) orientation, enhancing film quality and charge transport. PEDOT incorporation improved the surface morphology and reduced the defect density, leading to moderately enhanced light absorption across the visible range. Notably, the wide band gap of Se (∼1.9 eV) exhibits a strong spectral overlap with white LED emission, making it highly suitable for indoor light harvesting. While PEDOT slightly reduced performance under 1 sun, it significantly improved device efficiency under white LED illumination (1000 lx) by suppressing interfacial recombination. These results demonstrate the viability of Se/PEDOT heterostructures for efficient indoor energy harvesting and highlight their potential in low-power applications, such as the Internet of Things.