Polymer additives enhance charge transport balance in Y6 single-component organic solar cells

Engineering notes

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Chinese explanation / 中文解读

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Original abstract

The discovery of Y6 marks a considerable milestone in the development of bulk heterojunction (BHJ) organic solar cells (OSCs). The unique characteristics of Y6, including a small exciton binding energy and a long exciton diffusion length, have fueled the recent interest in exploring its use as the sole component in OSCs. Others have further shown that the power conversion efficiency (PCE) of such Y6-based single-component OSCs (SC-OSCs) can be enhanced by incorporating a small amount of polymer additives into the photoactive layer, ascribed to improved charge generation and reduced charge recombination. However, these effects have only been observed in specific conjugated polymers in separate studies, and a comprehensive investigation of the impact of different polymer additives and their blending amount on the device characteristics of the Y6-based SC-OSCs has not been performed. In this study, we investigated the influence of four polymer additives on the device performance and charge dynamics of the Y6-based SC-OSC. The additives include two conjugated polymers, poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PM6) and poly(3-hexylthiophene) (P3HT), and two non-conjugated polymers, polyvinylcarbazole (PVK) and polystyrene (PSt). Our results demonstrate that Y6-based SC-OSCs with polymer additives exhibit enhanced hole mobilities and more balanced charge transport, particularly with PM6 and PVK and even in the presence of the insulating polymer PSt, leading to performance enhancements in Y6-based SC-OSCs. Furthermore, the incorporation of PM6 or PVK can effectively reduce bimolecular/trap-assisted recombination, which contributes to improved photovoltaic performance. These results indicate that small amounts of polymer additives can enhance device performance by improving hole transport and suppressing recombination without requiring formation of a conventional donor-rich bulk heterojunction network, providing design guidelines for optimizing charge-transport balance in Y6-based SC-OSCs.

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