Tetrasubstituted Thieno[3,2- b]thiophenes as Hole-Transporting Materials for Perovskite Solar Cells

Three hole-transporting materials (HTMs) were prepared following a straightforward synthetic route by cross-linking arylamine-based ligands with a simple thieno[3,2-b]thiophene (TbT) core. The novel HTMs were fully characterized with standard techniques to gain insight into their optical and electrochemical properties and were incorporated in solution-processed mesoporous (FAPbI3)0.85(MAPbBr3)0.15 perovskite-based solar cells. The similar molecular structure of the synthesized HTMs was leveraged to investigate the role that the bridging units between the conjugated TbT core and the peripheral arylamine units plays on their properties and thereby on the photovoltaic response. A remarkable po…

High-Efficiency Perovskite Solar Cells using Molecularly-Engineered, Thiophene-Rich,Hole-Transporting Materials: Influence of Alkyl Chain Length on Power Conversion Efficiency

The synthesis and characterization of a series of novel small-molecule hole-transporting materials (HTMs) based on an anthra[1,2-b:4,3-b′:5,6-b′′:8,7-b′′′]tetrathiophene (ATT) core are reported. The new compounds follow an easy synthetic route and have no need of expensive purification steps. The novel HTMs were tested in perovskite solar cells (PSCs) and power conversion efficiencies (PCE) of up to 18.1 % under 1 sun irradiation were 2 measured. This value is comparable with the 17.8 % efficiency obtained using spiroOMeTAD as a reference compound. Similarly, a significant quenching of the Photoluminescence in the first nanosecond is observed, indicative of effective hole transfer.Additiona…

Isomerism effect on the photovoltaic properties of benzotrithiophene-based hole-transporting materials

Engineering of inorganic–organic lead halide perovskites for photovoltaic applications has experienced significant advances in recent years. However, the use of the relatively expensive spiro-OMeTAD as a hole-transporting material (HTM) poses a challenge due to dopant-induced degradation. Herein we introduce two new three-armed and four-armed HTMs (BTT-4 and BTT-5) based on isomeric forms of benzotrithiophene (BTT). The isomerism impact on the optical, electrochemical and photophysical properties and the photovoltaic performance is systematically investigated. Perovskite solar cells (PSCs) using BTT-4 and BTT-5 as HTMs show remarkable light-to-energy conversion efficiencies of 19.0% and 18.…

Dibenzoquinquethiophene- and Dibenzosexithiophene-Based Hole-Transporting Materials for Perovskite Solar Cells

Fused oligothiophene-based π-conjugated organic derivatives have been widely used in electronic devices. In particular, two-dimensional (2D) heteroarenes offer the possibility of broadening the scope by extending the π-conjugated framework, which endows enhanced charge transport properties due to the potential intermolecular π–π stacking. Here, the synthesis and characterization of two new small-molecule hole-transporting materials (HTMs) for perovskite solar cells (PSCs) are reported. The newly custom-made compounds are based on dibenzoquinquethiophene (DBQT) and dibenzosexithiophene (DBST) cores, which are covalently linked to triphenylamine moieties to successfully afford the four-armed …

Non-Planar and Flexible Hole-Transporting Materials from Bis-Xanthene and Bis-Thioxanthene Units for Perovskite Solar Cells

Two new hole-transporting materials (HTMs), BX-OMeTAD and BTX-OMeTAD, based on xanthene and thioxanthene units, respectively, and bearing p-methoxydiphenylamine peripheral groups, are presented for their use in perovskite solar cells (PSCs). The novelty of the newly designed molecules relies on the use of a single carbon-carbon bond ‘C−C’ as a linker between the two functionalized heterocycles, which increases the flexibility of the molecule compared with the more rigid structure of the widely used HTM spiro-OMeTAD. The new HTMs display a limited absorbance in the visible region, due to the lack of conjugation between the two molecular halves, and the chemical design used has a remarkably i…

Heteroatom Effect on Star-Shaped Hole-Transporting Materials for Perovskite Solar Cells

Molecular Engineering of Iridium Blue Emitters Using Aryl N‐Heterocyclic Carbene Ligands

The synthesis of a new series of neutral bis[2-(2,4-difluorophen-2-yl)pyridine][1-(2-aryl)-3-methylimidazol-2-ylidene]iridium(III) complexes is reported. Each complex has been characterized by NMR spectroscopy, UV/Vis spectrophotometry, and cyclic voltammetry, and the photophysical properties examined in depth. Furthermore, two of the complexes have been characterized by single-crystal X-ray diffraction analysis. By systematically modifying the cyclometalating aryl group on the N-heterocyclic carbene (NHC) ligand from 2,4-dimethoxyphenyl to 6-methoxy-2-methyl-3-pyridyl, the energy levels of the Ir complexes were modified to produce new blue emitters with increased HOMO and triplet-state ene…

Hole transporting materials based on benzodithiophene and dithienopyrrole cores for efficient perovskite solar cells

The development of highly efficient hole transporting materials (HTMs) for perovskite solar cells (PSCs) is still one of the most thrilling research subjects in the development of this emerging photovoltaic technology. Inner ring engineering of the aromatic core of new HTMs – consisting of three fused rings endowed with four triarylamine units – reveals major performance effects over the fabricated devices. In particular, substitution of the central pyrrole ring in dithienopyrrole (DTP) by a benzene ring – benzodithiophene (BDT) – allows enhancing the power conversion efficiency from 15.6% to 18.1%, in devices employing mixed-perovskite (FAPbI3)0.85(MAPbBr3)0.15 (MA: CH3NH3+, FA: NHCHNH3+) …

Hole-Transporting Materials for Perovskite Solar Cells Employing an Anthradithiophene Core

A decade after the report of the first efficient perovskite-based solar cell, development of novel hole-transporting materials (HTMs) is still one of the main topics in this research field. Two of the main advance vectors of this topic lie in obtaining materials with enhanced hole-extracting capability and in easing their synthetic cost. The use of anthra[1,9-bc:5,10-b'c']dithiophene (ADT) as a flat π-conjugated frame for bearing arylamine electroactive moieties allows obtaining two novel highly efficient HTMs from very cheap precursors. The solar cells fabricated making use of the mixed composition (FAPbI3)0.85(MAPbBr3)0.15 perovskite and the novel ADT-based HTMs show power conversion effi…

Perovskite Solar Cells: Heteroatom Effect on Star-Shaped Hole-Transporting Materials for Perovskite Solar Cells (Adv. Funct. Mater. 31/2018)

Saddle-like, π-conjugated, cyclooctatetrathiophene-based, hole-transporting material for perovskite solar cells

A flexible, saddle-like, π-conjugated skeleton composed of four fused thiophene rings forming a cyclooctatetrathiophene (CoTh) with four triphenylamines (CoTh-TTPA) is presented as a hole-transporting material (HTM) for perovskite solar cells. The new HTM shows a bright red color stemming from a direct conjugation between the TPA groups and the central CoTh scaffold. This results in a charge transfer band due to the combination of the weak acceptor moiety, the CoTh unit, and the electron-donating p-methoxytriphenylamine groups. CoTh-TTPA exhibits a suitable highest-occupied molecular orbital (HOMO) level in relation to the valence band edge of the perovskite, which ensures efficient hole ex…

High‐Efficiency Perovskite Solar Cells Using Molecularly Engineered, Thiophene‐Rich, Hole‐Transporting Materials: Influence of Alkyl Chain Length on Power Conversion Efficiency

The synthesis and characterization of a series of novel small-molecule hole-transporting materials (HTMs) based on an anthra[1,2-b:4,3-b′:5,6-b′′:8,7-b′′′]tetrathiophene (ATT) core are reported. The new compounds follow an easy synthetic route and have no need of expensive purification steps. The novel HTMs are tested in perovskite solar cells and power conversion efficiencies (PCE) of up to 18.1% under 1 sun irradiation are measured. This value is comparable with the 17.8% efficiency obtained using 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene as a reference compound. Similarly, a significant quenching of the photoluminescence in the first nanosecond is observed, ind…

Bis(arylimidazole) Iridium Picolinate Emitters and Preferential Dipole Orientation in Films

The straightforward synthesis and photophysical properties of a new series of heteroleptic iridium(III) bis(2-arylimidazole) picolinate complexes are reported. Each complex has been characterized by nuclear magnetic resonance, UV-vis, cyclic voltammetry, and photoluminescent angle dependency, and the emissive properties of each are described. The preferred orientation of transition dipoles in emitter/host thin films indicated more preferred orientation than homoleptic complex Ir(ppy)3.

CCDC 1445197: Experimental Crystal Structure Determination

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CCDC 1813461: Experimental Crystal Structure Determination

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CCDC 1445196: Experimental Crystal Structure Determination

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CCDC 1583689: Experimental Crystal Structure Determination

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CCDC 1583690: Experimental Crystal Structure Determination

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CCDC 1813460: Experimental Crystal Structure Determination

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CCDC 1813459: Experimental Crystal Structure Determination

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CCDC 1584183: Experimental Crystal Structure Determination

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