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Abstract Solar cells featuring polythiophenes as donors are one of the optoelectronic devices that hold notable promises for commercial application, profiting from the lowest synthetic complexity and excellent scalability. However, the complex phase behaviors of polythiophenes and their blends put constraints on modulating electrical performance and thus realizing stable performance under thermal stress. In this contribution, we present a multi‐technique approach that combines calorimetry, scattering, spectroscopy, and microscopy to thoroughly probe the thermodynamic mixing, thermal properties of materials, the evolution of nanoscale domain structure, and device performance of poly(3‐hexylthiophene) (P3HT) with a range of nonfullerene acceptors (NFAs) such as ITIC, IDTBR, and ZY‐4Cl. Accordingly, two blending guidelines are established for matching these popular NFAs with P3HT to enable highly efficient and thermally stable cells. First, blend systems with weak vitrification and hypo‐miscibility are excellent candidates for efficient solar cells. Furthermore, high thermal stability can be achieved by selecting NFAs with diffusion‐limited crystallization. The P3HT:ZY‐4Cl blend was found to endow the best performance of over 10% efficiency and an exceptionally high T80 lifetime of >6000 h under continuous thermal annealing, which are among the highest values for P3HT‐based solar cells. This realization of high thermal stability and efficiency demonstrates the remarkable potentials of simple polythiophene :nonfullerene pairs in electronic applications.

Owing to the advantages of low synthetic cost and high scalability of synthesis, polythiophene and its derivatives (PTs) have been of interest in the community of organic photovoltaics (OPVs). Nevertheless, the typical efficiency of PT based photovoltaic devices reported so far is much lower than those of the prevailing push-pull type conjugated polymer donors. Recent studies have underscored that the excessively low miscibility between PT and nonfullerene acceptor is the major reason accounting for the unfavorable active layer morphology and the inferior performance of OPVs based on a well-known PT, namely PDCBT-Cl and a non-halogenated nonfullerene acceptor IDIC. How to manipulate the miscibility between PT and acceptor molecule is important for further improving the device efficiency of this class of potentially low-cost blend systems. In this study, we introduced different numbers of F atoms to the end groups of IDIC to tune the intermolecular interaction of the hypo-miscible blend system (PDCBT-Cl:IDIC). Based on calorimetric, microscopic, and scattering characterizations, a clear relationship between the number of F atoms, miscibility, and device performance was established. With the increased number of F atoms in IDIC, the resulting acceptors exhibited enhanced miscibility with PDCBT-Cl, and the domain sizes of the blend films were reduced substantially. As a result, distinctively different photovoltaic performances were achieved for these blend systems. This study demonstrates that varying the number of F atoms in the acceptors is a feasible way to manipulate the molecular interaction and the film morphology toward high-performance polythiophene:nonfullerene based OPVs.

Developing novel solid additives has been regarded as a promising strategy to achieve highly efficient organic solar cells with good stability and reproducibility. Herein, a small molecule, 2,2'-(perfluoro-1,4-phenylene)dithiophene (DTBF), designed with high volatility and a strong quadrupole moment, is applied as a solid additive to implement active layer morphology control in organic solar cells. Systematic theory simulations have revealed the charge distribution of DTBF and its analog and their non-covalent interaction with the active layer materials. Benefitting from the more vital charge-quadrupole interaction, the introduction, and volatilization of DTBF effectively induced more regular and condensed molecular packing in the active layer, leading to enhanced photoelectric properties. Thus, high efficiency of over 17% is obtained in the DTBF-processed devices, which is higher than that of the control devices. Further application of DTBF in different active layer systems contributed to a deeper comprehension of this type of additive. This study highlights a facile approach to optimizing the active layer morphology by finely manipulating the quadrupole moment of volatile solid additives. [ABSTRACT FROM AUTHOR]