Stable Perovskite Solar Cells based on Hydrophobic Triphenylamine Hole-Transport Materials

Two hole-transporting materials (HTMs) based on N,N,N′,N′- tetraphenylbenzidine (TPB) and MeO-triphenylamine (MOTPA) are synthesized. The HTMs offer outstanding thermal stability, film-forming properties, and hole mobilities. Perovskite solar cells (PSCs) are prepared using either pristine HTM layers or layers doped with cobalt salts. The nondoped PSCs with as-synthesized HTMs show better performance compared to spiro-OMeTAD, especially for long-time stability in ambient air. The power conversion efficiency (PCE) of the cells decreases by only 3 % after 600 h of storage. The nondoped hole-transport layer (HTL) are hydrophobic, with a contact angle of 94.3° to water. The moisture-repelling ability of these HTMs are demonstrated by exposing the nondoped PSCs to an atmosphere saturated with water vapor. The PCE of doped PSCs with spiro-OMeTAD as HTL decreased 53 %, while that of nondoped PSCs with the as-synthesized HTMs as HTL only decreased 27 % after 15 min. These result thus show a new method to improve the operational stability of PSCs, especially at high humidity levels.