Oxoammonium enabled secondary doping of hole transporting material PEDOT:PSS for high-performance organic solar cells

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is one of the most widely used hole transporting materials in organic solar cells (OSCs). Multiple strategies have been adopted to improve the conductivity of PEDOT:PSS, however, effective strategy that can optimize the conductivity, work function, and surface energy simultaneously to reach a better energy alignment and interface contact is rare. Here, we demonstrate that oxoammonium salts (TEMPO+X−) with different counterions can act as facile and novel dopants to realize secondary doping of PEDOT:PSS. The effective charge transfer process achieved between TEMPO+X− and PEDOT:PSS results in enhanced carrier density and improved conductivity of PEDOT:PSS. Moreover, different counterions of TEMPO+X− can tune the work function and surface energy of PEDOT:PSS, enabling improved device performances. The resulting device with PM6:Y6 as the active layer shows a high power conversion efficiency (PCE) over 16%. Moreover, this doping strategy can also be applied to other conjugated polymers such as poly(3-hexylthiophene). This work provides a promising strategy to tune the properties of conjugated polymers through doping, thus effectively boosting the performance of organic solar cells.