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.

Automated summary

A new CPE composite was developed as a HTM for organic solar cells through rational molecular design and mutual doping mechanism, achieving high work function and good conductivity. It showed superior performance in different types of OSCs and achieved the highest photovoltaic efficiency so far.