20.46% Efficient Organic Solar Cells with Concurrent Voltage Enhancement and Thermal Stability Enabled by Crystallization-Kinetics-Controlled Morphology

Abstract

Organic solar cells are often limited by morphological instability and suboptimal phase separation, largely stemming from the rapid crystallization kinetics of state-of-the-art non-fullerene acceptors, which lead to excessive aggregation and metastable blends. Herein, we design an asymmetric acceptor, BTP-FClO, featuring slowed nucleation dynamics. When incorporated as a third component into PM6:L8-BO blends, BTP-FClO functions as a crystallization moderator, significantly delaying nucleation and phase separation. The refined morphology of the ternary blend is characterized by an extended nucleation time (199 ms) and a prolonged carrier lifetime, resulting in low energy disorder (13.8 meV) and a lower trap density (2.69 × 10¹⁶ cm⁻³). Thus, the ternary device overcomes the voltage–current trade-off to provide a power conversion efficiency of 20.46% by simultaneously increasing the open-circuit voltage (0.916 V) and short-circuit current density (28.02 mA cm⁻²). Notably, an efficiency of 18.28% is retained even at an active-layer thickness of 446 nm, underscoring excellent thickness tolerance. Moreover, the blend exhibits exceptional thermal stability, retaining 80% of its initial efficiency after annealing for 448 h at 60 °C, attributed to its robust morphology and high glass transition temperature (Tg =120 °C). This work demonstrates that molecular design targeting crystallization kinetics, alongside energetics, offers a practical pathway toward high-performance organic photovoltaics.