Research Progress of Hole Transport Materials Based on Spiro Aromatic-Skeleton in Perovskite Solar Cells

Abstract

The third-generation energy electro-optical technology, perovskite solar cells (PSCs), have risen fast over the past decade. In view of the characteristic of intrinsic-semiconductor of organic-inorganic hybrid perovskite materials, as well as the multilayer planar architecture of PSC devices, the hole transport materials (HTMs) based on organic small molecules were introduced PSCs to make up of p-type layer, by which not only full-solid state PSCs were established, but also the highly efficient and stable PSC devices were attained. Currently, spiro-OMeTAD (2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene) is still used as an universal benchmark material in the hole-transporting layer of PSCs, meanwhile the researches have make great effort to analyze and to improve the spiro-OMeTAD. For the prevailing molecule, the three-dimensional core of spirofluorene (SBF) offers a platform to integrate more hole-transporting units with less occupied space, and arylamine groups act as high electroactivity units due to their excellent p-type property. However, the classical SBF core has two major drawbacks: expensive preparation cost and monotonous modification positions, therefore the improvement orientation of spiro-OMeTAD is focused on the arylamine moieties. Along with the developments of molecular design of HTMs and corresponding synthetic methodology, a series of SBF-like aromatic-skeletons have been springing up and stepping into the field of HTMs in recent five years, e.g. spiro[fluorene-9,9′-xanthene], spiroacridine, spirothioxanthene and so on. These advancements expand the design space of HTM molecules, and enhance the efficiency and stability of PSCs. In consequence, we put eyes on the HTMs containing spiro aromatic-skeleton, and seek the structure elements of highly efficient materials. In this review, the high performance HTMs have been classified and summarized according to the type of spiro structure, further, their design solution and structure-performance relationship have also been refined. It is expected that the summarization and condensation would provide valuable strategies for HTMs design and promote the devel-

Evaluating Fluorinated-Aniline Units with Functionalized Spiro[Fluorene-9,9′-Xanthene] as Hole-Transporting Materials in Perovskite Solar Cells and Light-Emitting Diodes

“…The 1 H/ 13 C NMR spectra were obtained with a Bruker Avance500 II spectrometers (Billerica, MA, USA) at ambient temperature by utilizing deuteron dimethyl sulfoxide (DMSO-d 6 ) as a solvent and tetramethylsilane (TMS) as a standard. The mass spectra were obtained with a Waters Xevo G2-XS Tof (Milford, MA, USA).…”

“…Hence, a great deal of research works based on spiro compounds have been conducted to develop high-performance HTMs. By refining the research results, it can be found that spiro[fluorene-9,9′-xanthene] (SFX) is an ideal alternative to SBF, as the asymmetric spiro structure of SFX makes its derivatization and regulation more flexible than SBF [ 12 , 13 , 14 ]. For the electroactive units of HTMs, the electron-rich aniline-like segments are preferred because of their suitable properties, for instance, the lone pair of electrons of nitrogen atoms facilitate the formation of radical cation intermediates [ 15 ].…”