Stable perovskite solar cells with efficiency of 22.6% via quinoxaline-based polymeric hole transport material

Poor stability of spiro-OMeTAD hole transport materials (HTM) with dopant is a major obstacle for the commercialization of perovskite solar cell (pero-SC). Herein, we demonstrate a series of quinoxaline-based D-A copolymers PBQ5, PBQ6 and PBQ10 as the dopant-free polymer HTMs for high performance pero-SCs. The D-A copolymers are composed of fluorothienyl benzodithiophene (BDTT) as D-unit, difluoroquinoxaline (DFQ) with different side chains as A-unit, and thiophene as π-bridge, where the side chains on the DFQ unit are bi-alkyl for PBQ5, bi-alkyl-fluorothienyl for PBQ6, and alkoxyl for PBQ10. All the three copolymers are adopted as the dopant-free HTM in the pero-SCs. The planar n-i-p structured pero-SCs based on (FAP-bI3)0.98(MAPbBr3)0.02 with PBQ6 HTM demonstrated the high power conversion efficiency (PCE) of 22.6% with Voc of 1.13 V and FF of 80.8%, which is benefitted from the suitable energy level and high hole mobility of PBQ6. The PCE of 22.6% is the highest efficiency reported in the n-i-p structured pero-SCs based on dopant-free D-A copolymer HTM. In addition, the pero-SCs show significantly enhanced ambient, thermal and light-soaking stability compared with the devices with traditional spiro-OMeTAD HTM.