Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 13, Issue 30, Pages 36053-36061Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.1c07254
Keywords
organic solar cells; nonfullerene acceptors; side-chain engineering; morphology optimization; recombination suppression
Funding
- National Natural Science Foundation of China [21875286, 220]
- National Key Research & Development Program of China [2017YFA0206600]
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By optimizing the molecular structures of organic solar cell materials and developing novel acceptor molecules, high quantum efficiency and low voltage losses were achieved. Modification of alkyl chains led to improved fill factor, while shortening the alkyl chain enhanced solubility and crystallinity, ultimately improving the efficiency of the solar cells.
Optimizing the molecular structures of organic solar cell (OSC) materials and boosting the power conversion efficiencies are the eternal theme in the solar energy region. A series of fused benzotriazole (BTA)-based A-DA'D-A structures of nonfullerene acceptors (such as Y18) were developed for application in efficient OSCs, in which high quantum efficiencies and low voltage losses could be achieved because of the optimized electron-deficient core and specific molecular geometry. Here, based on the BTA core, the bulky alkyl chain on the BTA unit was further tailored to minimize the lateral alkyl chains and enhance the crystallinity while maintaining an adequate solubility. The resulting NFAs of BTA-C1, BTA-C5, and BTA-C6 are synthesized. Compared with the well-designed molecular Y18 (BTA-C8), we found that simply replacing the 2-ethylhexyl chain with a single methyl (BTA-C1) can easily improve the fill factor up to 77%, but its poor light absorption capacity and large domain size impeded further efficiency improvement. In particular, the BTA-C5, with a shortened branch alkyl chain of 2-methylbutyl, achieves suitable solubility and enhanced crystallinity. Significantly, owing to the balanced charge carrier mobility and suitable phase separation, the BTA-C5-based binary single-junction OSCs achieve a high efficiency of 17.11%, which is one of the top values in BTA-based OSCs.
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