A Nitroxide Radical Conjugated Polymer as an Additive to Reduce Nonradiative Energy Loss in Organic Solar Cells

Abstract

AbstractNonfullerene‐acceptor‐based organic solar cells (NFA‐OSCs) are now set off to the 20% power conversion efficiency milestone. To achieve this, minimizing all loss channels, including nonradiative photovoltage losses, seems a necessity. Nonradiative recombination, to a great extent, is known to be an inherent material property due to vibrationally induced decay of charge‐transfer (CT) states or their back electron transfer to the triplet excitons. Herein, it is shown that the use of a new conjugated nitroxide radical polymer with 2,2,6,6‐tetramethyl piperidine‐1‐oxyl side groups (GDTA) as an additive results in an improvement of the photovoltaic performance of NFA‐OSCs based on different active layer materials. Upon the addition of GDTA, the open‐circuit voltage (VOC), fill factor (FF), and short‐circuit current density (JSC) improve simultaneously. This approach is applied to several material systems including state‐of‐the‐art donor/acceptor pairs showing improvement from 15.8% to 17.6% (in the case of PM6:Y6) and from 17.5% to 18.3% (for PM6:BTP‐eC9). Then, the possible reasons behind the observed improvements are discussed. The results point toward the suppression of the CT state to triplet excitons loss channel. This work presents a facile, promising, and generic approach to further improve the performance of NFA‐OSCs.