Peng Qiang and Yan He’s EES: 17.33% Efficiency! High-Efficiency Non-Fullerene Organic Solar Cells
Release Date:
2020-09-02 14:37
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Over the past several decades, organic photovoltaics (OPV) have attracted considerable research attention. The recent emergence of polymer solar cells based on non-fullerene acceptors has significantly advanced the field of OPV. However, high-performance polymer solar cells to date are typically fabricated using halogenated solvents. These halogenated solvents pose risks to human health and the environment and are therefore unsuitable for industrial applications. Moreover, due to the limited solubility of non-halogenated solvents, it is challenging to achieve the desired morphological control, which in turn hinders their adoption in practical applications.
Recently, Qiang Peng from Sichuan University and He Yan from the Hong Kong University of Science and Technology reported a sophisticated aggregation-control strategy using halogen-free solvents, which successfully enabled the fabrication of high-performance non-fullerene PSCs with an efficiency of 17.33%—the highest value achieved to date for PSCs prepared from non-halogenated solvents.
PM6 and BTP-BO-4Cl were selected as the donor and acceptor, respectively, owing to their potential high performance and halogen-free solvent solubility. In addition, benzyl viologen (Bv) was introduced as a microstructure-improving additive to optimize and stabilize the morphology of PSCs, while also serving as an n-type dopant to enhance electron transport in PSCs.
The study found that BTP-BO-4Cl exhibits excellent solubility in chlorobenzene (CB), but its solubility in toluene (Tol) is highly temperature-dependent. The PM6:BTP-BO-4Cl blend is readily soluble in mild toluene conditions (above 50 °C); however, at room temperature, prolonged processing time leads to gradual crystallization and even precipitation of BTP-BO-4Cl. Therefore, pre-aggregation can be carried out prior to active-layer deposition, and the extent of aggregation can be directly tuned by adjusting the pre-processing delay time.
The results show that delaying the processing time leads to an optimized nano-fibrillar morphology of PM6:BTP-BO-4Cl. This facilitates charge dissociation and transport, thereby significantly enhancing device performance and successfully increasing the power conversion efficiency (PCE) from 15.69% to 17.33%. To date, this represents a new record for halogen-free solvent-treated PSCs. Importantly, this strategy can be further extended to other high-efficiency PSC systems, holding promise for precise morphological optimization and performance enhancement.
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