Additive-Free Non-Fullerene Organic Solar Cells

With the extensive research efforts paid over the past 30years, the power conversion efficiency of organic solar cells (OSCs) has been steadily improved from below 1% to greater than 16%. While fullerene derivatives have traditionally played a dominant role as acceptor materials in the first two decades, the distinctive advantages of non-fullerene acceptors, such as tunable energy levels, broad absorption, and improved device stability, have rendered them as the mainstream acceptors in OSCs, recently. However, in most cases, processing additives are required for morphology optimization of the photoactive layer, and these additives usually possess high boiling point, which makes it difficult to remove them completely. The residual additives would accelerate performance deterioration, leading to poor device stability. Furthermore, the tedious optimization of additives complicates device fabrication and decreases performance reproducibility. In this review, we summarize the recent works based on non-fullerene OSCs without using additives, affording insights into materials design and device fabrication for enabling highly efficient additive-free non-fullerene OSCs, which should be critical for the practical applications of OSCs.