A Nitroxide Radical Conjugated Polymer as an Additive to Reduce Non-Radiative Energy Loss in Organic Solar Cells.

Non-fullerene acceptor-based organic solar cells (NFA-OSCs) are now set off to the 20% power conversion efficiency (PCE) milestone. To achieve this, minimizing all loss channels, including nonradiative photovoltage losses, seems a necessity. Non-radiative 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. In this contribution, we show that the use of a new conjugated nitroxide radical polymer with 2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPO) 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, fill factor and short circuit current density improves 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). We then discuss the possible reasons behind the observed improvements. The results point towards the suppression of the CT state to triplet excitons loss channel. Our work presents a facile, promising, and generic approach to further improve the performance of NFA-OSCs. This article is protected by copyright. All rights reserved.