Benzotriazole-Based D-p-A-Type Photovoltaic Polymers Break Through 17% Efficiency

Benzo[d][1,2,3]triazole (BTA) unit is one of the most classic electron-accepting units (A) to construct donor (D)-& pi;-A-type photovoltaic polymers. However, the highest power conversion efficiency (PCE) of organic photovoltaics (OPVs) based on BTA-containing polymers is restricted to 15-16%, lagging other promising polymers. Thus, investigating the structure-performance relationship and breaking the efficiency bottleneck of BTA-based polymers is challenging but critical. Herein, the effects of fusing two thiophene rings at D (PE52), & pi; (PE4), and A (PE39) units of a classic D-& pi;-A-type BTA-containing polymer J52-Cl, respectively, on the backbone conformation, crystallinity, molecular stacking, and photovoltaic performance are systematically investigated. When blended with a BTA-containing non-fullerene acceptor (NFA), Y18, all three polymers with extending conjugated backbones can decrease the energy loss of photovoltaic devices. Notably, PE4, with a linear backbone conformation, realizes the champion PCE of 17.08%, with a short-circuit current density (JSC) of 26.83 mA cm-2, a large breakthrough for BTA-based photovoltaic polymers. What's more, the photovoltaic device based on PE4:Y18 combination fabricated by a non-halogenated solvent of o-xylene also displays an excellent PCE of 16.87%. The results indicate that fusing thiophene rings to BTA-polymers, especially at & pi;-bridge, is a simple and effective method to improve the photovoltaic performance via modulating the molecular conformation and crystallinity. Thiophene rings are fused on the donor (D), & pi;, and acceptor (A) units, respectively, to extend the conjugation length and fine-tune molecular conformation of the classic D-& pi;-A-type benzotriazole (BTA)-containing polymer. Thiophene fusion on the & pi;-bridge produces the linear backbone and the highest carrier mobilities, contributing to a champion power conversion efficiency above 17%, a breakthrough for BTA-based photovoltaic polymers.image