Intensive Exposure of Functional Rings of a Polymeric Hole-Transporting Material Enables Efficient Perovskite Solar Cells.

A variety of dopant-free hole-transporting materials (HTMs) is effectively applied in perovskite solar cells (PSCs); however, HTMs with the additional function of HTM/perovskite interfacial optimization that is crucial to their photovoltaic performance are really limited. In this work, the design of an HTM bearing an intensive exposure of its functional aromatic rings to perovskite layer via side-chain engineering is attempted. With an edge-on orientation and a short distance to perovskite, this HTM was expected to display an excellent ability to extract holes from and passivate defects in the perovskite layer. To demonstrate this strategy, an alternating copolymer was constructed with a 2,5-di-2-ethylhexyloxy-1,4-phenylene unit and a bithiophene unit, and the PSC based on this polymer showed an ultrahigh short-circuit current density of 25.50 mA cm-2 , which was the highest so far presented by dopant-free organic HTMs. A comparable power conversion efficiency of 19.68% (certified: 19.5%) to that of a control 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) device (19.81%) was thus obtained, which is the highest value ever reported for mesoporous PSCs based on dopant-free polymeric HTMs.