Spirobifluorene with an asymmetric fluorenylcarbazolamine electron-donor as the hole transport material increases thermostability and efficiency of perovskite solar cells

Abstract

The efficiency of perovskite solar cells utilizing spiro-OMeTAD as the hole transport material has been persistently enhanced, attaining the current 25.7%. However, these high-efficiency cells are unable to withstand the harsh heat at 85 °C. In this report, we present a spirobifluorene based hole transport material with highly asymmetric fluorenylcarbazolamine as the electron-donor, denoted as SBF-FC. Compared to spiro-OMeTAD, SBF-FC exhibits a comparable HOMO energy level, but the glass transition temperature is almost twice as high. The composite produced by blending SBF-FC and 4-tert-butylpyridinium bis(trifluoromethanesulfonyl)imide at an 85 : 15 weight ratio demonstrates a room temperature conductivity of 49 μS cm⁻¹ while retaining a high glass transition temperature of 176 °C. Importantly, the SBF-FC based hole transport layer, deposited onto the surface of a FAPbI₃ thin film, exhibits a more uniform morphology and remarkedly improved 85 °C durability, effectively suppressing the corrosion and decomposition of the perovskite film. By utilizing the SBF-FC based hole transport layer, we demonstrate perovskite solar cells achieving an average initial efficiency of 24.5% and long-term thermostability at 85 °C.