Efficient Selenium Photodiodes Based on an Inverted P-i-N Structure

Abstract

Selenium (Se) possesses high absorption coefficient, nontoxicity, and facile fabrication with low melting point, which makes it ideal for thin-film photovoltaics and photodetection. However, most of the reported Se-based photodiodes were based on a conventional N-i-P structure, and the planar devices based on an inverted P-i-N structure are barely reported. In this work, vacuum-evaporated Se thin films were introduced to fabricate efficient inverted Se photodiodes. In addition, we also fully characterize the Se thin films via time-resolved microwave conductivity and deep level transient spectroscopy, and the charge carrier dynamics of the trap states were systematically investigated. Based on the understanding of the fundamental properties and device optimization, we achieved solar cells with a high power conversion efficiency of 4.85%. Furthermore, the Se-based photodiodes also exhibited excellent performance for photodetection, including an extremely low dark current of ∼1 nA cm–2, a fast response time of <1 μs, and high specific detectivity, which have great potential for real applications.