Highly efficient and stable organic solar cells achieved by improving exciton diffusion and splitting through a volatile additive-assisted ternary strategy

The ternary and additive strategy, introducing a third component into a binary blend and add suitable additives, opens a simple and promising avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). This study investigates the optimization of OSCs by introducing volatile additives and a third component, L8-BO-X, which tunes the active layer morphology and improves the performance of the devices. Utilizing various characterization techniques, such as the grazing-incidence wide-angle X-ray scattering (GIWAXS), film-depth-dependent light absorption spectroscopy (FLAS), and the femtosecond-resolved transient absorption (fsTA) spectroscopy, the effects of these adjustment on crystallinity, phase separation, exciton generation, and charge transport in photovoltaic device are explored. The incorporation of the third component and volatile additives results in less anisotropy in molecular orientation and thus faster exciton splitting at the D-A interface, enhanced π-π stacking coherence length and longer exciton lifetime, and eventually an enhanced power conversion efficiency (PCE) of 19.6 % (certified as 19.07 % in the National Institute of Metrology in China) and exceptional photostability, with the devices retaining 82 % efficiency after 1200 hours of continuous light exposure.