Low-cost planar organic small molecules as hole transport materials for high efficient perovskite solar cells

Abstract

Planar organic small molecular hole transport materials (HTMs) have been vigorously developed and utilized in perovskite solar cells (PSCs) with impressive power conversion efficiencies (PCE). However, the price of common HTMs, for instance Spiro-OMeTAD is expensive due to its tedious synthesis and low product yields, it remains challenging to develop high-performance and low-cost organic small molecular HTMs. In this work, a series of molecule, as planar HTMs were constructed by combined carbazole core with planar donor phenothiazine or phenoxazine as backbone, and 1,2-diethoxyethane or n-hexane as side chains, ca. TEG-CZ-PTZ, TEG-CZ-POZ, He-CZ-PTZ and He-CZ-POZ. The results showed that phenoxazine-based TEG-CZ-POZ and He-CZ-POZ have better hole transport efficiency than the phenothiazine-based TEG-CZ-PTZ and He-CZ-PTZ. Meanwhile, TEG-CZ-PTZ and TEG-CZ-POZ with 1,2-diethoxyethane as side chains on carbazole core performed better in hole transporting process than He-CZ-PTZ and He-CZ-POZ with n-hexane. Thus, the PSC based on TEG-CZ-POZ has achieved a best PCE of 21.03%, outperforming the PSCs based on Spiro-OMeTAD (20.74%). More importantly, the estimated cost for lab-synthesis of TEG-CZ-POZ is much lower than that of Spiro-OMeTAD (46.3 $/g vs 92 $/g), suggesting its promising application for efficient and low-cost PSCs.