Novel efficient hole-transporting materials based on a 1,1′-bi-2-naphthol core for perovskite solar cells

Abstract

New star-shaped and efficient hole-transporting materials based on a 1,1′-bi-2-naphthol central core for perovskite solar cells are developed via facile synthesis. The 1,1′-bi-2-naphthol is first applied into the field of perovskite solar cells. The 2,7-carbazole-bis(4-methoxy-phenyl)-amine and 3,6-carbazole-bis(4-methoxy-phenyl)-amine are used as end groups. A reference compound based on a 3,3′-biphenyl core is prepared as well. The new materials have suitable highest occupied molecular orbital levels to match well with the valence band of CH₃NH₃PbI₃, and they all exhibit a glass transition temperature higher than 160 °C. A device fabricated by hole-transporting materials based on 1,1′-bi-2-naphthol and 2,7-carbazole-bis(4-methoxy-phenyl)-amine in conjunction with a carbon counter electrode achieves the highest power conversion efficiency of 8.38% under the illumination of 100 mW cm⁻², which is comparable to that fabricated by commercial spiro-OMeTAD (8.73%). Dark current, IPCE and IMVS measurements are also discussed. The introduction of 2,7-carbazole-bis(4-methoxy-phenyl)-amine onto the 1,1′-bi-2-naphthol central core tends to enhance J_sc of a device, and 3,6-carbazole-bis(4-methoxy-phenyl)-amine improves V_oc. This work provides a new series of hole-transporting materials to fabricate economic and efficient perovskite solar cells.