Enhancing the performance of inverted organic photovoltaics: Zn-doped TiO₂ as an efficient electron transport layer

Various metal-doped titanium dioxide (TiO₂) materials have emerged as promising electron transport layers (ETLs) for enhancing the performance of inverted organic photovoltaic (OPV) devices. Among these, zinc (Zn) stands out as a particularly effective dopant for TiO₂. Incorporating zinc into TiO₂ can enhance its electrical conductivity, energy level alignment, and interfacial charge transport properties, effectively addressing the inherent limitations of pristine TiO₂. So, in this study, inverted OPV devices were fabricated using benzodithiophene (PTB7) blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₀BM) as the active layer. The power conversion efficiency (PCE) of devices using Zn-doped TiO₂ as the ETL was 7.87 %, which was ∼16 % higher than the 6.79 % obtained with undoped TiO₂. At the Zn-doped TiO₂/active layer interface, this improvement is ascribed to decreased trap states, enhanced electron mobility, and inhibited charge recombination. Moreover, Zn doping facilitated superior energy level alignment, enabling more efficient charge extraction. These results demonstrate Zn-doped TiO₂'s potential as a viable ETL for highly effective inverted OPVs. The study also emphasizes how crucial material doping techniques are to maximizing ETL characteristics and promoting the creation of reasonably priced organic solar cells.