Hole-Transporting Materials with a Two-Dimensionally Expanded π-System around an Azulene Core for Efficient Perovskite Solar Cells

Abstract

Two-dimensionally expanded π-systems, consisting of partially oxygen-bridged triarylamine skeletons that are connected to an azulene (1-3) or biphenyl core (4), were synthesized and characterized. When tetra-substituted azulene 1 was used as a hole-transporting material (HTM) in perovskite solar cells, the observed performance (power conversion efficiency = 16.5%) was found to be superior to that of the current HTM standard Spiro-OMeTAD. A comparison of the hole mobility, the ability to control the HOMO and LUMO levels, and the hole-collection efficiency at the perovskite/HTM interface in 1 with reference compounds (2-4 and Spiro-OMeTAD) led to the elucidation of key factors required for HTMs to act efficiently in perovskite solar cells.

Light Intensity Dependence of Performance of Lead Halide Perovskite Solar Cells

“…Perovskite solar cells were fabricated with a twostep method, following the previous reports [20,21]. .…”

“…Figure 1 shows the steady-state absorption spectrum of a typical perovskite solar cell (FTO/cTiO 2 /mp-TiO 2 /MAPbI 3 /OMeTAD/Au). From the previous study [21,24], the film thickness is estimated to be 300 nm. The spectral shape with a shoulder around 750 nm is in agreement with the previous report [18].…”

Synthesis of Azole-fused Benzothiadiazoles as Key Units for Functional π-Conjugated Compounds

“…Moreover, in thiazole-fused BT units, the electronic structure could be further modulated by varying the oxidation state of the sulfur atom in methylthio group at the fused thiazole ring. A variety of D-A molecules and polymers would be developed using these electron-accepting units by combining with various electron-donating and -conjugated units [25][26][27][28][29][30][31][32], which is currently in progress in our laboratory.…”

Partially Oxygen-Bridged Triphenylamines with a Quasiplanar Structure as a Key Scaffold for Hole-Transporting Materials

“…For the core skeleton, we selected the nonbenzenoid aromatic hydrocarbon azulene, which exhibits a unique electron donating and accepting character that arises from the ve and seven membered rings, respectively. Using HND Azulene 5 as a HTM in perovskite solar cells led to high PCEs (16.5%), 8 even when compared to Spiro OMeTAD (Figure. …”

“…As model compounds for oxygen bridged triphenylamines, we designed and synthesized dimers 1 4, 7 as well as the π extended derivatives 5 7, which contain an azulene core. 8 The utility of these compounds as HTMs was demonstrated by their incorporation in OLEDs (1 4) 9 and perovskite solar cells (5 7) 8 ( Figure 3). Two highly important points to consider during the molecular design and development of model compounds for organic electronics applications are structural simplicity and intrinsically high stability.…”