n-doped inorganic molecular clusters as a new type of hole transport material for efficient organic solar cells

Summary At present, PEDOT:PSS and MoO3 are the most widely used hole transport layer (HTL) in organic solar cells (OSCs); however, some drawbacks still limit their practical use. In this study, we developed a facile method to enhance the conductivity of a polyoxometalate-based inorganic cluster (PIC) without sacrificing its high work function nature. An inorganic cluster HPMO:Sn with excellent hole collection ability was prepared and used as an HTL in an OSC achieving a power conversion efficiency (PCE) of 17.3%. To the best of our knowledge, the photovoltaic performances are among the best devices reported in the field. Moreover, HPMO:Sn possesses the merits of a definite and stable chemical structure and is low cost, and HPMO:Sn can be easily prepared without any post-treatment. Besides, we prove that the HPMO:Sn HTL is very compatible with blade coating, i.e., an OSC of 1.0 cm2 was fabricated using a blade-coated HPMO:Sn film to attain an efficiency of 15.1%.