Separating Crystallization Process of P3HT and O-IDTBR to Construct Highly Crystalline Interpenetrating Network with Optimized Vertical Phase Separation

The morphology with the interpenetrating network and optimized vertical phase separation plays a key role in determining the charge transport and collection in polymer:nonfullerene small molecular acceptors (SMAs) solar cells. However, the crystallization of polymer and SMAs usually occurs simultaneously during film-forming, thus interfering with the crystallization process of each other, leading to amorphous film with undesirable lateral and vertical phase separation. The poly(3-hexylthiophene) (P3HT):O-IDTBR blend is selected as a model system, and controlling film-forming kinetics to solve these problems is proposed. Herein, a cosolvent 1,2,4-triclorobenzene (TCB) with selective solubility and a high boiling point is added to the solution, leading to prior crystallization of P3HT and extended film-forming duration. As a result, the crystallinity of both components is enhanced significantly. Meanwhile, the prior crystallization of P3HT induces solid-liquid phase separation, hence rationalizing the formation of the nano-interpenetrating network. Moreover, the surface energy drives O-IDTBR to enrich near the cathode and P3HT to migrate to the anode. Consequently, a highly crystalline nano-interpenetrating network with proper vertical phase separation is obtained. The optimal morphology improves charge transport and suppresses bimolecular recombination, boosting the power conversion efficiency from 4.45% to 7.18%, which is the highest performance in P3HT-based binary nonfullerene solar cells.