Air-processed, efficient CH3NH3PbI3−xClx perovskite solar cells with organic polymer PTB7 as a hole-transport layer

Low-temperature, solution-processed perovskite solar cells (PSCs), which utilized organic poly[4,8-bis[(2-ethylhexyl) oxy] benzo[1,2-b: 4,5-b'] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b]-thiophenediyl] (PTB7) as a hole-transport layer (HTL), achieved a power conversion efficiency (PCE) as high as 13.29% when fabricated in ambient air. Through a comparative study, we demonstrate this PCE value to be superior compared to its counterparts with spiro-OMeTAD or P3HT as the HTL; the superiority consists of a higher fill factor (FF) and open-circuit voltage (V-oc). By probing the absorption spectrum of CH3NH3PbI3-xClx before and after spin-coating the PTB7, it is discovered that the spin coating of PTB7 has little influence on the quality of the perovskite films. Furthermore, it is shown that PTB7 possesses higher conductivity compared with conventional HTLs, including spiro-OMeTAD, P3HT and PCDTBT. Moreover, in order to further improve device performance, the prevalent additives lithium bis (trifluoromethylsulphony) imide (LiTFSI) and 4-tert-butylpyridine (t-Bp) are investigated, along with a post-annealing process that is applied to the whole device. The results presented here and the overall fabrication method represent a helpful new approach for fabricating highly efficient perovskite-based photovoltaic devices.