Intensification of Vertical Phase Separation for Efficient Polymer Solar Cell via Piecewise Spray Assisted by a Solvent Driving Force

Piecewise spray has the advantage of controlling the component distribution, i.e., constructing vertical phase‐separated active layers, to improve the charge generation efficiency of large‐scale polymer solar cells. However, it brings a connection problem because of the drastic difference in the donor/acceptor ratio of continuous coatings using the conventional solvent. Assisted by 1,3,5‐trimethylbenzene‐based solvent engineering, a solvent driving force is formed, resulting in a continuous interface for piecewise spray‐coated active layers. The blend film forms a bicontinuous interpenetrating network in the active layer and provides efficient percolation pathways for charge carrier transport, resulting in a considerable improvement in the photovoltaic performance. When the donor/acceptor ratio is 1:2 in the first coating and 2:1 in the second coating, and the thickness of each coating is 90 nm, the performance of the PBDB‐T‐2Cl:IT4F photovoltaic device shows a notable conversion efficiency of 12.29% with a high short‐circuit current density of 21.55 mA cm⁻². Importantly, this piecewise spray technique can be used for large‐scale module fabrication.