A dichlorobenzene-functionalized hole-transporting material (HTM) is developed for a CH3NH3PbI3-based perovskite solar cell. Notwithstanding the similarity of the frontier molecular orbital energy levels, optical properties, and hole mobility between the functionalized HTM [a polymer composed of 2′-butyloctyl-4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate (TT-BO), 3′,4′-dichlorobenzyl-4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate (TT-DCB), and 2,6-bis(trimethyltin)-4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene (BDT-EH), denoted PTB-DCB21] and the nonfunctionalized polymer [a polymer composed of thieno[3,4-b]thiophene (TT) and benzo[1,2-b:4,5-b′]dithiophene (BDT), denoted PTB-BO], a higher power conversion efficiency for PTB-DCB21 (8.7 %) than that for PTB-BO (7.4 %) is achieved because of a higher photocurrent and voltage. The high efficiency is even obtained without including additives, such as lithium bis(trifluoromethanesulfonyl)imide and/or 4-tert-butylpyridine, that are commonly used to improve the conductivity of the HTM. Transient photocurrent–voltage studies show that the PTB-DCB21-based device exhibits faster electron transport and slower charge recombination; this might be related to better interfacial contact through intermolecular chemical interactions between the perovskite and the 3,4-dichlorobenzyl group in PTB-DCB21.
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