This review summarizes the fundamentals, solution processing methods, optimization strategies and various applications of MoO3 in OPVs.

Power conversion efficiencies (PCEs) and device stability are two key technical factors restricting the commercialization of organic solar cells (OSCs). In the past decades, though the PCEs of OSCs have been significantly enhanced, device instability, especially in the state-of-the-art nonfullerene system, still needs to be solved. In this work, an effective crosslinker (namely, DTODF-4F), with conjugated fluorene-based backbone and crosslinkable epoxy side-chains, has been designed and synthesized, which is introduced to enhance the morphological stabilization of the PM6:Y6-based film. This crosslinker with two epoxy groups can be in situ crosslinked into a stable network structure under ultraviolet radiation. We demonstrate that DTODF-4F, which acted as a third component, can promote the exciton dissociation rate and reduce traps/defects, finally resulting in the enhancement of efficiency. In particular, the OSC devices exhibit better stability under continuous heating owing to the morphology fixation of the bulk heterojunction. This work drives the development direction of morphological stabilization to further improve the performance and stability of OSCs.

The development of new electron transporting layer (ETL) materials to improve the charge carrier extraction and collection ability between cathode and the active layer has been demonstrated to be an effective approach to enhance the photovoltaic performance of organic solar cells (OSCs). Herein, water-soluble carbon dots (CDs) as ETL material have been creatively synthesized by a vigorous chemical reaction between polyethylenimine (PEI) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) via a simple one-step hydrothermal method. Taking full advantage of the high electron transfer property of PTCDA and the work function (W F) reduction ability of PEI, CD gained high electron mobility due to its large π-conjugated area and reduced the W F of indium tin oxide (ITO) by 0.75 eV. As for the photovoltaic performance of devices, inverted OSCs based on CDs have achieved a high power conversion efficiency (PCE) of 17.35%, exhibiting no burn-in effect with no reduction in PCE after more than 4000 h of storage. The successful application of CDs in OPV has developed a new avenue for designing efficient ETL materials that benefits the photovoltaic performance of OSCs.

Sensible selection of host blends and the third component is crucial to give full play to the advantages of the ternary strategy for achieving high efficiency polymer solar cells (PSCs)....