High-performance perovskite solar cells based on dopant-free hole-transporting material fabricated by a thermal-assisted blade-coating method with efficiency exceeding 21%

As the performance in terms of efficiency and device stability of perovskite solar cells (PSCs) has made rapid progress in a short period of time, the upscaling of PSCs becomes an important issue for massive commercial applications, where the cost of device manufacturing is a determining factor for wide spread uses. Device fabrication by printing technique is one such low-cost process for large scale preparation. However, one of the reasons limiting the progress of a fully printed PSCs is the lack of appropriate hole-transporting materials (HTMs) that can be printed. Herein, a new donor-acceptor-donor (D-A-D) type hole-transporting material with 4-dicyanomethylene-4H-cyclopenta[2,1-b;3,4-b']dithiophene (diCN-CPDT) core tethered with two bis(alkoxy) diphenylaminocarbazole periphery groups, namely CB, was synthesized and applied as dopant-free HTM in fully printed PSCs by thermal-assisted blade-coating (TABC) method. The PSCs fabricated by fully scalable processes based on dopant-free CB as HTM exhibited an impressive power conversion efficiency (PCE) up to 21.09%, which is higher than that of devices with doped 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene (spiro-OMeTAD) (14.28%) under the same fabricating condition. Furthermore, the all TABC process is demonstrated to produce an area of 10 cm x 10 cm for the devices except for electrode with an average PCE of 19.68%. Additionally, the TABC-based dopant-free CB-based PSCs exhibited significantly improved long-term stability, retaining more than 94% PCE after 500 h compared to that using doped spiro-OMeTAD under a relative humidity of similar to 50%. This result demonstrated that the newly developed CB is a promising candidate HTM for high-performance fully printable PSCs.