Pre- and post-treatments free nanocomposite based hole transport layer for high performance organic solar cells with considerably enhanced reproducibility

In this work, we demonstrate a one-step room-temperature ethanol-processed nickel oxide (NiOx):electron acceptor nanocomposite functioning as efficient hole transport layer (HTL). Specifically, one-step refers to the formation of the nanocomposite HTL films without extra steps of pre-treatments of ITO nor post-treatments of HTL films, and thus considerably reduce the fabrication complexity and cost. By varing the concentration of the electron acceptor, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), the work function (WF) of the nanocomposite films can be widely tuned from 4.73eV to 5.30eV, which favors its use for photovoltaic applications of organic donor materials with different highest energy occupied molecular orbital (HOMO) energy levels. Organic solar cells (OSCs) have been fabricated by using the NiOx:F4-TCNQ nanocomposite as HTL. The optimized average power conversion efficiency (PCE) of NiOx:F4-TCNQ based OSCs can be 18% better than that of one-step prepared poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) based OSCs. Remarkably, NiOx:F4-TCNQ based OSCs show better reproducibility as the deviation of PCE values can be improved by a greatest extent of 10 times. This work contributes towards simple and low-cost fabrication of high efficiency OSCs for practical photovoltaic applications.