Novel hole transporting materials based on cyclopentadithiophene for perovskite solar cells

We have demonstrated three LY-HTMs for perovskite solar cells in this report. These LY-HTMs embed cyclopentadithiophene (CPT) core that incorporates 2∼4 triphenylamine electron donor units. Designing LY-HTMs with Lewis-basic property of carbonyl or imine, can effectively passivate the defects of insufficiently coordinated Pb²⁺ in the perovskite layer. The LY-HTMs have good thermal stability and enhanced intermolecular interaction, thereby dense packing, due to the sulfur-sulfur interaction in the dithiophene structure. Moreover, the sulfur-sulfur interaction achieves a deeper HOMO energy level that can be well-matched to perovskite solar cells (PSCs). It also improves the charge mobility to enhance Voc and Jsc values. The best performance using LY-1 as a HTM in PSCs exhibited a Jsc of 23.1 mA∙cm⁻², a Voc of 1.06 V, and a fill factor of 0.78, corresponding to an overall conversion efficiency of 19.12% (the control device of spiro-OMeTAD, 17.69%). In addition, the PCEs of the LY-1 PSC devices underwent decays of only 90% and 74.8% of their original values after 10 and 30 days, respectively, under an Ar atmosphere.