Journal
ACS OMEGA
Volume 6, Issue 7, Pages 4562-4573Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsomega.0c04495
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Funding
- National Research Foundation (NRF) [NRF-2019R1A2C1003679]
- Korea Institute of Energy Technology Evaluation and Planning (KETEP) of the Republic of Korea [20173010012960]
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Two nonfullerene small molecules, TBTT-BORH and TBTT-ORH, are developed as electron acceptors for organic solar cells, with different alkyl groups influencing intermolecular aggregation and solubility. The introduction of a butyloctyl group greatly improves material solubility in TBTT-BORH, while a solvent-vapor annealing treatment effectively enhances film morphology. OSCs based on these acceptors and polymer donor PTB7-Th achieve good power conversion efficiency.
Two nonfullerene small molecules, TBTT-BORH and TBTT-ORH, which have the same thiophene-benzothiadiazole-thiophene (TBTT) core flanked with butyloctyl (BO)- and octyl (O)-substituted rhodanines (RHs) at both ends, respectively, are developed as electron acceptors for organic solar cells (OSCs). The difference between the alkyl groups introduced into TBTT-BORH and TBTT-ORH strongly influence the intermolecular aggregation in the film state. Differential scanning calorimetry and UV-vis absorption studies reveal that TBTT-ORH exhibited stronger molecular aggregation behavior than TBTT-BORH. On the contrary, the material solubility is greatly improved by the introduction of a BO group in TBTT-BORH, and the inevitably low molecular interaction and packing ability of the as-cast TBTT-BORH film can be effectively increased by a solvent-vapor annealing (SVA) treatment. OSCs based on the two acceptors and PTB7-Th as a polymer donor are fabricated owing to their complementary absorption and sufficient energy-level offsets. The best power conversion efficiency of 8.33% is obtained with the SVA-treated TBTT-BORH device, where, together with a high open-circuit voltage of 1.02 V, the charge-carrier mobility and the short-circuit current density were greatly improved by the SVA treatment to levels comparable to those of the TBTT-ORH device because of the suppressed charge recombination and improved film morphology. In this work, the simultaneous improvement of both material solubility and device performance is achieved through alkyl side-chain engineering to balance the trade-offs among material solubility/crystallinity/device performance.
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