In recent years, solution processed bulk heterojunction (BHJ) organic solar cells (OSCs) have been intensively studied. The widely used fullerene derivatives as acceptors, (e.g. [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 70 BM)), widely used, display a limited visible light absorption and unsatisfactory thermal stability in combination with amounts of donor materials. It was found that rational design rules for novel donors and introduced analysis of non-fullerene acceptors (NFAs) are employed to develop novel systems overcoming these limitations. Here we reported a new small molecule donor, W-CN, containing dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) donor unit and 2-ethylhexyl-cyanoacetate (CN) acceptor unit with thiophene-thieno[3,2-b]thiophene (T-TT) bridge. We chose 2,2'-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC), 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis (4-hexylphenyl)-dithieno[2,3-d:2′, 3′-d']-s-indaceno[1,2-b:5,6-b']dithiophene) (ITIC) and PC 70 BM as the acceptors. Furthermore, we demonstrated all-small molecule solar cells (all-SMSCs) based on W-CN:IDIC and W-CN:ITIC composites with decent performance with the power conversion efficiencies (PCEs) of 5.26% and 3.89%, respectively. In contrast, W-CN:PC 70 BM solar cell shows a slightly higher PCE of 5.94% as compared to the investigated NFA systems. Nevertheless, W-CN:IDIC and W-CN:ITIC systems exhibit better thermal stability as compared to the W-CN:PC 70 BM system. Notably, solar cells based on W-CN:IDIC system maintain almost 96% initial performance after baking at 100 °C for 24 h under inert atmosphere. The highly promising findings demonstrated the importance of novel structure-property relationships for the rational design strategies of photovoltaic materials and suitable selection of acceptors for high performance OSCs.
- Fullerene derivative
- Morphological evolution
- Non-fullerene acceptor
- Structure-property relationship
- Thermal stability