Solution-processable MoO_x nanocrystals enable highly efficient reflective and semitransparent polymer solar cells

Highlights: • MoO₃ nanocrystal film HTLs can be as effective as evaporated MoO₃ films. • Using solution processed MoO₃ HTL PCE of 9.5% is obtained for PTB7-Th:PC₇₁BM. • The universal applicability of s-MoO₃ nanocrystals verified for OPVs and PLEDs. • A novel transparent anode of MoO₃ nanocrystals with Ag nanowires is demonstrated. • Highly efficient semitransparent OPVs with PCE ~6.5% are obtained with FF>60 %. Solution-manufacturing of organic solar cells with best-in-class power conversion efficiency (PCE) will require all layers to be solution-coated without compromising solar cell performance. To date, the hole transporting layer (HTL) deposited on top of the organic bulk heterojunction layer in the inverted architecture is most commonly an ultrathin (x suspension with carefully controlled nanocrystal (NC) size can yield state of the art reflective and semitransparent solar cells. Using NCs smaller than the target HTL thickness (∼10 nm) can yield compact, pinhole-free films which result in highly efficient polymer:fullerene bulk heterojunction (BHJ) solar cells with PCE=9.5%. The solution processed HTL is shown to achieve performance parity with vacuum-evaporated HTLs for several polymer:fullerene combinations and is even shown to work as hole injection layer in polymer light emitting diodes (PLED). We also demonstrate that larger MoO_x NCs (30–50 nm) successfully composite MoO_x with Ag nanowires (NW) to form a highly conducting, transparent top anode with exceptional contact properties. This yields state-of-the-art semitransparent polymer: fullerene solar cells with PCE of 6.5% and overall transmission >30%. The remarkable performance of reflective and semitransparent OPVs is due to the uncommonly high fill factors achieved using a carefully designed strategy for implementation of MoO_x nanocrystals as HTL materials.