High-efficiency organic solar cells processed from a halogen-free solvent system

The use of non-halogenated solvents for the green manufacture of high-efficiency organic solar cells (OSCs) is important for their future application. However, the power conversion efficiency (PCE) of the non-halogenated solvent processed OSCs is generally lower than their halogenated counterpart due to the poor film microstructure caused by the solubility issue. Herein, we propose a halogen-free solvent system to optimize film microstructure of the photovoltaic blend based on the polymer donor D18 and small-molecule acceptor (SMA) L8-BO towards high-efficiency OSCs. The solvent system is consisted of a main solvent carbon disulfide and an additive paraxylene, where the former ensures the good solution-processability and promotes the solution aggregation of L8-BO, and the latter can finely control the phase-separation process by selectively dissolving the SMA. This solvent combination robustly produces a high-quality active layer, i.e., the bicontinuous networks of donor and acceptor with nano-sized phase-separation and strong & pi;-& pi; stacking. With the effective charge generation, transport and collection, the resulting device from the non-halogenated solvent system shows a high PCE of 17.50%, which is comparable to that of the device prepared from the halogenated solvent chloroform (ca. 17.11%). This article proposes a new strategy for the green fabrication of high-efficiency OSCs to accelerate their industrialization.

Automated summary

Using non-halogenated solvents for the green manufacture of high-efficiency organic solar cells (OSCs) is crucial for their future application. However, the poor film microstructure caused by solubility issues leads to lower power conversion efficiency (PCE) compared to halogenated solvent processed OSCs. This study proposes a halogen-free solvent system that optimizes the film microstructure and achieves high-efficiency OSCs. The solvent system, consisting of carbon disulfide and paraxylene, produces a high-quality active layer with efficient charge generation, transport, and collection, resulting in a comparable PCE to the device prepared from a halogenated solvent. This article presents a new strategy for the green fabrication of high-efficiency OSCs to accelerate their industrialization.