Dithieno[3,2-b:2 ',3 '-d]pyrrole-based hole transport materials for perovskite solar cells with efficiencies over 18%

Dithieno[3,2-b: 2',3'-d]pyrrole (DTP) derivatives are one of the most important organic photovoltaic materials due to better pi-conjugation across fused thiophene rings. In this work, two new hole transport materials (HTMs), H16 and H18, have been obtained through a facile synthetic route by cross linking triarylamine-based donor groups with a 4-(4-methoxyphenyl)-4H-dithieno[3,2-b: 2',3'-d]pyrrole (MPDTP) and N-(4-(4H-dithieno[3,2 b: 2',3'-d]pyrrol-4-yl) phenyl)-4-methoxy-N-(4-methoxyphenyl) aniline (TPDTP) unit, respectively. The H16 HTM outperforms the H18 in terms of conductivity, hole mobility, and hole transport at the interface. This result could be attributed to the enhancement of the conductivity, hole mobility and high quality of the film exerted by the MPDTP core. The optimized device based on H16 exhibits a high power conversion efficiency (PCE) of 18.16%, which is comparable to that obtained with the state-of-the-art-HTM spiro-OMeTAD (18.27%). Furthermore, the long-term aging test shows that the H16 based device has good stability after two months of aging under controlled (20%) humidity in the dark. Importantly, the synthesis cost of H16 is roughly 1/5 of that of spiro-OMeTAD. The present finding highlights the potential of DTP based HTMs for efficient PSCs.