A Generally Applicable Approach Using Sequential Deposition to Enable Highly Efficient Organic Solar Cells

Bulk-heterojunction (BHJ) organic solar cells (OSCs) are prepared by a common one-step solution casting of donor-acceptor blends often encounter dynamic morphological evolution which is hard to control to achieve optimal performance. To overcome this hurdle, a generally applicable, sequential processing approach has been developed to construct high-performance OSCs without involving tedious processes. The morphology of photoactive layers comprising a polymer donor (PM6) and a nonfullerene acceptor (denoted as Y6-BO) can be precisely manipulated by tuning Y6-BO layer with a small amount of 1-chloronaphthalene additive to induce the structural order of Y6-BO molecules to impact the blend phase. The results of a comparative investigation elucidate that such two-step procedure can afford more favorable BHJ microstructure than that achievable with the single blend-casting route. This translates into improved carrier generation and transport, and suppressed charge recombination. Consequently, the devices based on sequential deposition (SD) deliver a remarkable efficiency up to 17.2% (the highest for SD OSCs to date), outperforming that from the conventional BHJ devices (16.4%). The general applicability of this approach has also been tested on several other nonfullerene acceptors which show similar improvements. These results highlight that SD is a promising processing alternative to promote better photovoltaic performance and reduce production requirements.