Efficient and Stable Organic Solar Cells with PM6:Y6-Based Photoactive Layer Enabled by p-Type Doping

The introduction of molecular doping process is necessary to enhance the optic and electronic properties of organic semiconductors for facilitating charge transport. In particular, since the doping process has a positive influence on the charge transfer interaction between the host semiconductor and dopant, improved mobility has been efficiently achieved via these doping methods using p- or n-type dopants. Despite its advantages, doping technologies in organic solar cells (OSCs), which are generally known to have better hole mobility, are restricted to the development of n-type dopants used for balancing the electron and hole as increasing the electron mobility. In addition, since the bulk-heterojunction (BHJ) microstructure in OSCs has randomly blended phases of the donor and acceptor, it is important to optimize charge extraction without loss by controlling the morphology. In this study, we report OSCs by p-type doping with formic acid into a BHJ photoactive layer comprised of PM6 and Y6. The resulting champion device yields a significantly improved power conversion efficiency from 14.3% to 15.3% with a high fill factor of 71.7%. It is found that the p-doped photoactive layer exhibits enhanced conductivity, carrier mobilities, and suppressed charge recombination. The p-type dopant, formic acid, also acts as a film morphology modifier of the photoactive layer with enhanced phase separation to transport the charge efficiently. This work demonstrates that controlling the charge transport via introducing a small amount of dopant into the devices with not-only small-area but also printed large-area photoactive layers is a promising strategy for further improvement of device efficiency and stability in OSCs.