Copolymers based on thiazolothiazole-dithienosilole as hole-transporting materials for high efficient perovskite solar cells

• Two novel copolymers, with priorities in light absorption and hole mobility, were applied as HTL materials in perovskite solar cells.
• To balance the charge transportation, pristine C60 was employed as interlayer at the cathode side.
• With the two above-mentioned interlayers, a PCE as high as 15.83% was achieved.

The interlayers, including hole transporting layer (HTL) and electron transporting layer (ETL), segregating photoactive layer and the electrodes play an important role in charge extraction and transportation in perovskite solar cells (pero-SCs). Two novel copolymers, PDTSTTz and PDTSTTz-4, for the first time were applied as HTL in the n-i-p type pero-SCs, with the device structure of ITO/compact TiO2/CH3NH3PbI3-xClx/HTL/MoO3/Ag. The highest occupied molecular orbitals (HOMO) levels of PDTSTTz and PDTSTTz-4 exhibit a suitable band alignment with the valence band edge of the perovskite. Both of them lead to improved device performances compared with reference pero-SCs based on P3HT as HTL. To further balance the charge extraction and the diffusion length of charge carriers, pristine C60 was introduced at the cathode side of the pero-SCs, working together with TiO2 as ETL. With insertion of both the HTL and ETL, the performance of pero-SCs was greatly enhanced. The optimized devices exhibited impressive PCEs of 14.4% and 15.8% for devices based on PDTSTTz and PDTSTTz-4. The improved performance is attributed to better light harvest ability, decreased interface resistance and faster decay time due to the introduction of the interlayers.

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