Star-shaped carbazole-based BODIPY derivatives with improved hole transportation and near-infrared absorption for small-molecule organic solar cells with high open-circuit voltages

Abstract

A series of tunable absorbing star-shaped BODIPY derivatives containing a different number of carbazole units were designed and synthesized. With the extended conjugated skeleton, their absorption spectra become progressively bathochromic shifted from the red region to the near-infrared region. The compound TAC with four carbazole units exhibits a strong near-infrared absorption up to 850 nm with a high extinction coefficient over 135 000 M⁻¹ cm⁻¹ and considerable intrinsic hole mobility of 4.82 × 10⁻⁵ cm² V⁻¹ s⁻¹ in SCLC devices. The near-infrared organic solar cells (OSCs) based on TAC exhibit a potential power conversion efficiency of 2.70% and a high open-circuit voltage of 0.85 V.