Due to the simple structure and excellent scalability, poly-3-hexylthiophene (P3HT) becomes much popular as a low-cost donor polymer partner with the emerging nonfullerene acceptors in recent years. Presently, P3HT used in the high-performance nonfullerene solar cells are all prepared by the traditional Grignard metathesis method, which is not sustainable compared with direct arylation polymerization. The application and the molar mass dependence of direct arylation polymerized P3HT in fullerene-free organic solar cells have not been explored yet. In this work, five batches of P3HT with weight-average molar mass ranging from ~9 kg/mol to ~90 kg/mol were prepared via direct arylation polymerization (Figure 1a), with the aim to detail the interaction-performance relationships in the state-of-the-art P3HT:nonfullerene photovoltaic blend, namely P3HT:ZY-4Cl. Our thermodynamic analysis revealed that the amorphous-amorphous interaction parameters strongly depend on the P3HT molar mass and can be varied by a factor of 2.7 (Figure 1b). Owing to the best π-π stacking order deduced from grazing incidence X-ray diffraction and the smallest domain size, the blend based on the medium molar mass batch (26 kg/mol) delivered the highest current density, fill factor, and power conversion efficiency up to 9.6% among the five systems (Figure 1c). Our established relationships may be applied to screen the best molar mass batch for P3HT-based organic photovoltaics.

Surpassing 9.6% efficiency for P3HT: Nonfullerene solar cells by delicate control of miscibility

ACS Spring Meeting 2021

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