Abstract:As a new generation of solid-state film cells, organic solar cells have a power conversion efficiency of close to 15% as reported in the literature; they have become an important research topic in the field of renewable energy sources. Hole transport materials (HTMs), an import constituent of organic solar cells, significantly affect the power conversion efficiency and stability of organic solar cells. The hole transport materials recently used in organic solar cells can be divided into two main categories: inorganic hole transport materials (IHTMs) and organic hole transport materials (OHTMs). Although organic solar cells constructed on IHTMs have an excellent power conversion efficiency, their large-scale manufacturing is not possible because of vacuum evaporation plating process. Recently, a large number of OHTMs have been designed, synthesized, and successfully used in organic solar cells. The development of diverse OHTMs with better energy-level matching and higher hole mobility is an effective method to increase the power conversion efficiency and stability of organic solar cells; therefore, it has become the focus of current research and development. Currently, PEDOT:PSS is one of the most commonly used OHTMs. However, because of its acidity and hygroscopicity, PEDOT:PSS is unfavorable for the long-term stability of organic solar cells, hindering its long-term manufacturing and application. OHTMs based on conjugated electrolytes have been evaluated, providing a good increase in power conversion efficiency. In this paper, the effects of molecular structure of conjugated electrolyte-based OHTMs on power conversion efficiency, fill factor, open-circuit voltage, short-circuit current, and stability are summarized. Furthermore, the energy level, hole mobility, and use of additives are discussed. Although still some problems exist in the application of OHTMs, their flexible modification provides an open designing space. The coexistence of challenge and opportunity in this field suggests that with the innovation of OHTMs, organic solar cells with high power conversion efficiency, high stability, and large-scale manufacturing will emerge in the near future, and such organic solar cells have excellent commercialization prospect.