Modulating the Mixing Gibbs Free Energy to Enhance Solid–Liquid Phase Separation for High-Performance Organic Solar Cells

摘要

Organic solar cells (OSC) feature a hierarchical structure with the electrondonor/acceptor layer sandwiched by anode and cathode, which raises theimportance of controlling the molecular crystal orientation, domain size, andvertical distribution to facilitate the charge collection at electrodes. However,the similar conjugated backbone of donor/acceptor material and fast filmformationkinetics have led to spinodal-decomposition-orientated phaseseparation that result in the film presenting an intimately mixed morphologyand random molecular orientation. To solve the issue, the mixing Gibbs freeenergy-triggered solid–liquid phase separation during the film formation processis enhanced by solidifying one component and solvating the other basedon a liquid additive. Following the liquid evaporation process, a favorablevertical distribution is obtained. Meanwhile, the prolonged solvation processenlarges the domain size and assists the molecules to diffuse and orientproperly, enabling better exciton/charge dynamics during the power conversionprocesses. As a result, the fabricated devices exhibit a fill factor over 80and an efficiency of 18.72, which is one of the top efficiencies for binaryOSCs. Insights and a methodology is provided here to manipulate the organicdonor/acceptor phase separation in terms of mixing Gibbs free energy.