Universal Hole Transporting Material via Mutual Doping for Conventional, Inverted, and Blade-Coated Large-Area Organic Solar Cells

Conjugated polyelectrolytes (CPEs) have been widely used as hole transporting materials (HTMs) in optoelectronic devices due to their good film-forming ability. However, the low work function (WF) and poor conductivity of CPEs are long-standing issues that limit their performances and applications. Herein, by a rational molecular design and an innovative mutual doping mechanism, we developed a new CPE composite PIDT-F:phosphomolybdic acid (PIDT-F:PMA) that can be used as HTM in diverse types of organic solar cells (OSCs), such as conventional, inverted, and blade-coated large-area devices. The redox reaction between the CPE PIDT-F and phosphomolybdic acid (PMA) has a synergistic effect that significantly increases the doping density by nearly 2 orders of magnitude. Such mutual doping is an effective approach to simultaneously obtain ultrahigh WF and good conductivity in HTMs. Notably, the PIDT-F:PMA HTM showed superior hole collection ability over poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and achieved a high photovoltaic efficiency (PCE) of 17.6%, representing the highest PCE in OSCs with a pH-neutral solution-processed HTM so far. Furthermore, PIDT-F:PMA can form smooth films on both hydrophilic and hydrophobic substrates; therefore, the HTM could also be used to fabricate inverted and blade-coated large-area OSCs, showing high PCEs of 16.9 and 16.4%, respectively. We believe that such a design strategy will pave a new path for the exploration of highly efficient and universal HTMs for diverse OSCs.