Photovoltaic properties of metal-free semiconductor DMEDA·I6: A first-principles investigation

Abstract Metal-free halide materials have garnered significant attention. However, because of their large band gap, current metal-free materials are not suitable as solar cell absorbers. A metal-free semiconductor, DMEDA·I6, with a narrow band gap (∼1.36 eV) and strong light absorption, is a promising candidate for solar cell absorbers. Using the first-principles calculation method, a systematic investigation was conducted on the photovoltaic properties of DMEDA·I6, including electronic properties, variation trend of the band gap under strain, defect physics, and band alignments of solar cell interfaces. It was found that DMEDA·I6 crystallized in a one-dimensional I chain with alternating long and short I–I bond lengths. Although both the valence band maximum and conduction band minimum of DMEDA·I6 are derived from the I p states, their compositions are distinguishable owing to the abnormal I–I bond arrangement. The band gap of DMEDA·I6 increases when the lattice volume expands, which is similar to that of the popular lead-based perovskites and opposite to that of the conventional zincblende semiconductors. Among the intrinsic defects, only defect VI can produce a deep defect level in the band gap. The formation of VI can be suppressed under the I-rich preparation conditions; thus, I rich condition is proposed when preparing DMEDA·I6 solar cell absorbers. Commonly used hole transportation materials are suitable for DMEDA·I6-based solar cells, whereas electron transport materials (ETMs) with a lower lowest unoccupied molecular orbital than commonly used ETMs should be used.