An oligothiophene derivative named DR3TBDTT with high hydrophobicity was synthesized and functioned as the hole transporting material without an ion additive. 8.8% of power conversion efficiency was obtained for CH3NH3PbI3-xClx based planar solar cells with improved stability, compared to devices using Li-TFSI doped spiro-MeOTAD.

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This paper presents an in-depth understanding of the essential differences of organic small-molecule thin films at the molecular level via vacuum deposition and solution processes for organic light-emitting diodes (OLEDs). Synchrotron-based two-dimensional grazing incidence X-ray diffraction has been used to investigate the essential difference. The result reveals that tris(4-carbazoyl-9-ylphenyl)amine (TCTA) molecules show highly oriented arrangements, that is, face-to-face π−π stacking, in vacuum-deposited films, unlike the randomly arranged molecules in spin-coated films. The faceto-face π−π stacking behavior of the molecules in a vacuum-deposited TCTA film leads to higher hole-transport mobility, which is the essential reason for the higher efficiency of a vacuum-deposited OLED compared with that of a solution-processed counterpart, consistent with the calculation results.