Hydrophobic Hole-Transporting Materials Incorporating Multiple Thiophene Cores with Long Alkyl Chains for Efficient Perovskite Solar Cells

Two hydrophobic hole transporting materials (HTMs) carrying multiple thiophene cores of 5,7-bis(3-hexylthiophen-2-yl)-2,3-dihydrothieno[3,4-b][1,4]dioxine (for SP-01) or 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (for SP-02) and long alkyl substituents have been prepared through facile routes with high yields, together with the hole-transporting molecule 2,5-bis(4,4'-bis(methoxyphenyl)aminophen-4 ''-yl)-3,4-ethylene dioxythiophene (H101) as reference compound. The structure-property relationships of these HTMs for perovskite solar cells have been systematically investigated. It is found that introducing hydrophobic alkyl chains into HTMs can retard interfacial charge recombination and, specifically, improve stability owing to the enhanced moisture resistance. Perovskite solar cells based on SP-01 give an overall conversion efficiency of 12.37% without, and 13.91% with the addition of FK102, respectively. These values are better than that of H101 (11.59%) and comparable to that of the standard spiro-OMeTAD (12.95%). Moreover, the devices based on hydrophobic HTMs SP-01 show better stability under similar to 40% humid atmosphere than those based on H101 and spiro-OMeTAD, which paves the way for developing new HTMs combining high efficiency, low cost, and excellent stability features by appropriate structural modifications. (C) 2016 Elsevier Ltd. All rights reserved.