Long coherence lengths (CLs) of crystals and proper intermixed phase amount guarantee charge transport and exciton dissociate efficiently, which is crucial for organic solar cells (OSCs) to achieve high device performance. However, extending CLs usually reduces the intermixed phase, leading to an insufficient interface for exciton dissociation. Herein, a strategy using a binary polymer with different molecular weights as donor is employed, that is, poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) with high (P3HT‐H) and low (P3HT‐L) molecular weight are blended as donor, and (5Z,5′Z)‐5,5′‐(((4,4,9,9‐tetraoctyl‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(benzo[c][1,2,5]thiadiazole‐7,4‐diyl))bis(methanylylidene))bis(3‐ethyl‐2‐thioxothiazolidin‐4‐one) (O‐IDTBR) is used as acceptor. In kinetics, the entanglements of P3HT‐H are relieved due to the higher molecular diffusivity of P3HT‐L. In thermodynamics, the miscibility of P3HT‐L/O‐IDTBR, P3HT‐H/O‐IDTBR, and P3HT‐L/P3HT‐H blends increases in turn. Hence, P3HT forms a more ordered structure with longer CLs after adding P3HT‐L, which also drives O‐IDTBR dispersed in P3HT crystalline regions diffuse to the O‐IDTBR crystalline regions to further self‐organize. Consequently, the CLs of both P3HT and O‐IDTBR are extended, while keeping the intermixed phase amount proper. The optimized microstructure boosts device performance from 7.03% to 7.80%, which is one of the highest values reported for P3HT/O‐IDTBR blends. This is a novel way to solve the conflict mentioned above, which may provide guidance to finely regulating the morphology of the active layer.

Solution–processed organic solar cells (OSC) have been explored widely due to their low cost and convenience, and impressive power conversion efficiencies (PCEs) which have surpassed 18%. In particular, the optimization of film morphology, including the phase separation structure and crystallinity degree of donor and acceptor domains, is crucially important to the improvement in PCE. Considering that the film morphology optimization of many blends can be achieved by regulating the film–forming process, it is necessary to take note of the employment of solvents and additives used during film processing, as well as the film–forming conditions. Herein, we summarize the recent investigations about thin films and expect to give some guidance for its prospective progress. The different film morphologies are discussed in detail to reveal the relationship between the morphology and device performance. Then, the principle of morphology regulating is concluded with. Finally, a future controlling of the film morphology and development is briefly outlined, which may provide some guidance for further optimizing the device performance.

Organic solar cells (OSCs) have unique advantages of low-cost solution processing, light weight, flexibility, and semitransparency, which is a promising photovoltaic technology. The intermixed phase plays a key role in determining the power conversion efficiencies (PCE) of OSCs. The intermixed phase is an amorphous region, where the donor and acceptor mix at the molecular level.Great efforts have been devoted to optimize the content and the composition of the intermixed phase. This perspective focuses on the functions of intermixed phase and elaborates the relationship between intermixed phase behavior and photophysical process, in particular, the exciton dissociation and charge transport. Then the characterization methods, including quantitative and qualitative characterizations, for the content and composition of intermixed phases are introduced. Meanwhile, this review also introduces the strategies to control the intermixed phase behavior, such as adjusting the miscibility between donor and acceptor, changing the ratio of donor to acceptor, regulating the crystallinity and so on. Moreover, representative examples are given and discussed to understand the key parameters on tuning the intermixed phase behavior. Finally, a future controlling and development of intermixed phase behavior is briefly outlooked, which may help to achieve high PCE of OSCs.

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