Room temperature solution processed tungsten carbide as an efficient hole extraction layer for organic photovoltaics

Abstract

We demonstrated tungsten carbide (WC) as an efficient anode buffer layer for a high-performance inverted organic solar cell. The devices based on active layers comprised of either poly(3-hexylthiophene) (P3HT) or poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) mixed with fullerene derivatives have achieved power conversion efficiencies (PCEs) of 3.83% and 8.04%, respectively. The WC layer was deposited onto the active layer from a surfactant-free nanoparticle alcohol solution because the buffer layer was well functionalized, removing the requirement for oxygen-plasma or annealing treatment, while simultaneously allowing for optimum photogenerated charge-carrier collection in an inverted structure device. The WC-based device displayed an improved stability performance compared with the MoO₃-based one. The anode buffer layer introduced here was easy to implement and compatible with solution processed organic photovoltaics, and therefore applicable for potential cost-effective manufacturing processes.