Dihydrobenzofuran-C60 bisadducts as electron acceptors in polymer solar cells: Effect of alkyl substituents

• A series of novel dihydrobenzofuran-C60 bisadducts were synthesized by a facile method and utilized as acceptor materials in polymer solar cells.
• Device performances were significantly improved by using the alkyl chain substituted dihydrobenzofuran-C60 bisadducts (Cn-BFCBA) as acceptors.
• When n = 4, i.e. tert-butyl as substituent (C4-BFCBA), PCE of the corresponding device reached 3.40%, which is comparable to that of the device based on PC61BM.

A series of novel dihydrobenzofuran-C60 bisadducts, denoted by BFCBA (without side chain substituent) and Cn-BFCBA (n represents the number of carbon atoms on side chain substituent, and varies as 1–5), were synthesized by a facile method and utilized as acceptor materials in polymer solar cells (PSCs). These fullerene bisadducts were found to possess similar optical, electrochemical properties but the PSCs based on them as acceptors present very diverse photovoltaic performance as the variation of n. Compared to the PSC based on BFCBA, device performances were significantly improved by the application of alkyl chain substituted dihydrobenzofuran-C60 bisadducts (Cn-BFCBA). In particular, when n = 4, i.e. tert-butyl used as substituent, PCE of the corresponding device reached to a summit of 3.40%. This result is comparable to that of the device based on PC61BM as acceptor. The morphology studied by AFM and electron mobility investigated by the space charge limited current (SCLC) method further revealed that C4-BFCBA shows a reasonably well miscibility with P3HT and a significantly higher electron mobility. These properties might account for its optimal photovoltaic performance among these series of the fullerene bisadducts. For comparison, dihydrobenzofuran-C60 monoadduct and trisadduct based on tert-butyl substituents were also synthesized. The corresponding PSC device test results showed that C4-BFCBA present much better photovoltaic performance than its corresponding monoadduct (C4-BFCMA) and trisadduct (C4-BFCTA) as well as BFCBA.

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