Donor–π–donor type hole transporting materials: marked π-bridge effects on optoelectronic properties, solid-state structure, and perovskite solar cell efficiency

Paek, Sanghyun; Zimmermann, Iwan; Gao, Peng; Gratia, Paul; Rakštys, Kasparas; Grancini, Giulia; Nazeeruddin, Mohammad Khaja; Rub, Malik Abdul; Kosa, Samia A.; Alamry, Khalid A.; Asiri, Abdullah M.

doi:10.1039/c6sc01478j

Cited by 88 publications

(43 citation statements)

References 30 publications

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“…Although most of them need additives and/or dopants to work appropriately as HTM, [95] researchers have found some that can work as intrinsic p-type conductors without any additive agents. They have the advantages of easy synthesis, strong π-conjugation for strong intermolecular interaction, and a convenient supply chain from traditional organic electronic studies.…”

Section: D Linear Small Moleculementioning

confidence: 99%

Less is More: Dopant‐Free Hole Transporting Materials for High‐Efficiency Perovskite Solar Cells

Zhou

Wen

Gao

2018

Advanced Energy Materials

252

217

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years, the demands for reducing the fabrication costs and the energy payback time of photovoltaic devices led to the invention of emerging third-generation PV technologies, such as dye-sensitized solar cells (DSSCs), organic photovoltaic (OPV), quantum dots solar cells, and the latest perovskite solar cells (PSCs). Among them, PSC is the only technology that combines both merits of low processing energy cost and high power conversion efficiency (PCE), which makes it possible to replace the silicon-based PV technology.Since the first reports by Bach and Grätzel et al. about the use of 2,2′,7,7′tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) as the hole-transporting material (HTM) in solid-state DSSCs (ssDSSC), spiro-OMeTAD becomes the benchmark of all the new HTMs developed for ssDSSC and PSCs. Contrary to the popular myth, spiro-OMeTAD is not completely amorphous but a semi-crystalline organic p-type semiconductor with a glass transition temperature of 121 °C and a melting point of 246 °C. [1] Its chemical structure is shown in Figure 1a and Grätzel's lab first revealed the crystal structure in 2014 [2] ( Figure 1b). It has a large bandgap of 2.98 eV and yields almost colorless thin films when deposited from solution in organic solvents such as toluene or chlorobenzene. The first oxidation potential of spiro-OMeTAD is found to be approximately −5.1 eV as derived from electrochemical and photoelectron spectroscopy measurements. [3] In the case of the solid-state PSCs reported since 2012, [4,5] the PCE of lab-made devices has increased from 9.7% [6] to above 21% [7] in 2017, owing to the improvement in the perovskite composition and device engineering. However, on account of several desirable properties, (i) favorable glass transition temperature; (ii) reasonable solubility; (iii) proper ionization potential; (iii) low visible light absorption; and (iv) appropriate solid-state morphology, spiro-OMeTAD has remained as the material of choice when high PCEs are demanded. Due to the fact that spiro-OMeTAD suffers from a relatively low conductivity in its pristine form, all the eyecatching PCEs were achieved by adding additives and/or dopants-a standard technique used to tune the electrical properties of both organic and inorganic semiconductors. Typical additives including 4-tert-butylpyridine (TBP) and lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI) were added to the spin-coating formulation of spiro-MeOTAD and Perovskite solar cells have delivered power conversion efficiency beyond 22% in less than seven years, implying the potential for the paradigm shift of lowcost photovoltaics with high efficiency and low embedded energy. Besides the "perovskite fever," the development of new hole transport materials (HTM), especially dopant-free HTMs, is another research hotspot. This is because the currently used HTMs, such as spiro-OMeTAD derivatives, require additional chemical doping process to ensure sufficient conductivity and proper ionic potential level for efficient hole transport and colle...

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Section: D Linear Small Moleculementioning

confidence: 99%

Less is More: Dopant‐Free Hole Transporting Materials for High‐Efficiency Perovskite Solar Cells

Zhou

Wen

Gao

2018

Advanced Energy Materials

252

217

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“…Recently,o rganic-inorganic halide perovskite solar cells (PSCs) have attracted considerable attention because of their outstanding performance in converting sunlight to electricity at al ow cost compared with silicon-based photovoltaict echnology.T he first PSCs, as ana-lyzed by Miyasaka in 2009, had power conversion efficiency (PCE) of 3.8 %. [12][13][14] To overcome these issues, numerouss tudies have focusedo nl ow-costp roduction without as piro-based linkage in the HTM, mainly using acene, [15] carbazole, [16][17][18][19][20][21][22][23] indole, [24][25][26] phenothiazine, [27] phenoxazine, [28] thiophene, [29][30][31][32][33][34][35] triarylamine, [36][37][38][39] triazateuxene, [40][41][42][43] and truxene. [11] In the conventional devicec onfiguration, 2,2',7,7'-tetrakis[N,N-di(4methoxyphenyl)amino]-9,9'-spirobifluorene( Spiro-OMeTAD) is generally used as the hole-transporting material( HTM) and has demonstrated PCEs of 20-21 %i nP SCs.…”

Section: Introductionmentioning

confidence: 99%

Facilely Synthesized spiro[fluorene‐9,9′‐phenanthren‐10′‐one] in Donor–Acceptor–Donor Hole‐Transporting Materials for Perovskite Solar Cells

Chen

Huang

et al. 2018

ChemSusChem

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We have demonstrated two novel donor-acceptor-donor (D-A-D) hole-transport material (HTM) with spiro[fluorene-9,9'-phenanthren-10'-one] as the core structure, which can be synthesized through a low-cost process in high yield. Compared to the incorporation of the conventional HTM of commonly used 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD), the synthesis process is greatly simplified for the presented D-A-D materials, including a minimum number of purification processes. This results in an increased production yield (>55 %) and suppressed production cost (<30 $ g ), in addition to high power conversion efficiency (PCE) in perovskite solar cells (PSCs). The PCE of a PSC using our D-A-D HTM reaches 16.06 %, similar to that of Spiro-OMeTAD (16.08 %), which is attributed to comparable hole mobility and charge-transfer efficiency. D-A-D HTMs also provide better moisture resistivity to prolong the lifetime of PSCs under ambient conditions relative to their Spiro-OMeTAD counterparts. The proposed new type of D-A-D HTM has shown promising performance as an alternative HTM for PSCs and can be synthesized with high production throughput.

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“…[1] Rigid and planar shapes have ag reater tendency to form crystalline domains. [5] Ty pical frameworks to elaborate such materials include biphenyl, [6] triphenylamine, [7] and spirobifluorene. [5] Ty pical frameworks to elaborate such materials include biphenyl, [6] triphenylamine, [7] and spirobifluorene.…”

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confidence: 99%

Topological Transformation of π‐Conjugated Molecules Reduces Resistance to Crystallization

et al. 2017

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Tw oe lectronically delocalized molecules were designed as models to understand howm olecular shape impacts the tradeoff between solubility and crystallization tendencies in molecular semiconductors.T he more soluble compound TT contains an on-planar bithiophene central fragment, whereas CT has ap lanar cyclopentadithiophene unit. Calorimetry studies show that CT can crystallizem ore easily than TT.H owever,a bsorption spectroscopys hows that the initially amorphous TT film can eventually form crystals in which the molecular shape is significantly more planar.T wo thermally reversible polymorphs for TT were observed by XRD and grazing-incidence wide-angle X-rays cattering (GIWAXS) measurements.T hese findings are relevant within the context of designing soft semiconductors that exhibit high solubility and atendency to providestable organized structures with desirable electronic properties.

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Donor–π–donor type hole transporting materials: marked π-bridge effects on optoelectronic properties, solid-state structure, and perovskite solar cell efficiency

Abstract: Donor–π-bridge–donor type oligomers (D–π–D) have been studied intensively as active materials for organic optoelectronic devices.

Cited by 88 publications

References 30 publications

Less is More: Dopant‐Free Hole Transporting Materials for High‐Efficiency Perovskite Solar Cells

Less is More: Dopant‐Free Hole Transporting Materials for High‐Efficiency Perovskite Solar Cells

Facilely Synthesized spiro[fluorene‐9,9′‐phenanthren‐10′‐one] in Donor–Acceptor–Donor Hole‐Transporting Materials for Perovskite Solar Cells

Topological Transformation of π‐Conjugated Molecules Reduces Resistance to Crystallization

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