Durable polymer solar cells produced by the encapsulation of a WSe2 hole-transport layer and beta-carotene as an active layer additive

Two-dimensional (2D) tungsten diselenide (WSe2), a novel layered transition metal dichalcogenide (TMDC) with a fascinating structure and remarkable functionalities, has been extensively investigated for various promising applications, including photodetectors, photocatalysis, and solar cells. In this work, WSe2 nanoflakes (NF-WSe2) have been obtained by liquid-phase exfoliation. In addition, the unique crystalline structure and desirable electrical properties of the as-exfoliated NF-WSe2 in polymer solar cells (PSCs) are presented. Notably, NF-WSe2 can effectively boost hole transport in PSCs, attributed to its higher uniformity on indium tin oxide (ITO), suitable ionization potential (IP) and enhanced charge transport properties. PSCs based on the ternary bulk-heterojunction poly[N-9 '-heptadecanyl-2,7-carbazole-alt-5,5-(4 ',7 '-di-2-thienyl-2 ',1 ',3 '-benzothiadiazole)] (PCDTBT):[6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) + beta-carotene (bCar) with NF-WSe2 as the hole transport layer (HTL) are realized with superior photovoltaic characteristics. Furthermore, the implementation of the NF-WSe2 HTL also prominently increases the long-term durability of PSCs compared with that of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) reference cells. This study represents a milestone for the integration of WSe2 in the enhancement of device performance in PSCs.