Dopant‐Free Donor (D)–π–D–π–D Conjugated Hole‐Transport Materials for Efficient and Stable Perovskite Solar Cells

Liu, Xicheng; Yi, Chenyi; Bi, Dongqin; Luo, Jingshan; Wang, Shirong; Zhao, Xiaoming; Xiao, Yin; Zakeeruddin, Shaik M.; Grätzel, Michaël

doi:10.1002/cssc.201600905

Cited by 84 publications

(60 citation statements)

References 56 publications

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“…This is partly because of the dopants that work well with spiro‐OMeTAD might not be suitable for these three HTMs . Moreover, the dopants seem to have a negative impact on the film morphology which can be seen from the SEM image in Figure ; similar behavior was also observed in other reports . The statistical data of the perovskite solar cells containing the TP1 based on 10 identical devices are shown in Figure c, indicating good device reproducibility.…”

Section: Figuresupporting

confidence: 84%

Efficient, Stable, Dopant‐Free Hole‐Transport Material with a Triphenylamine Core for CH₃NH₃PbI₃ Perovskite Solar Cells

Pan

Liu

et al. 2017

Energy Tech

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A star‐shaped hole‐transporting material (HTM) using the triphenylamine (TPA) as the core named TP1 is designed and synthesized. The implementation of the new HTM in CH3NH3PbI3‐based perovskite solar cells exhibits an excellent overall power conversion efficiency (PCE) of 12.63 % without the use of any dopants and additives, which is comparable to the 14.93 % obtained using p‐doped spiro‐OMeTAD. Importantly, the devices based on TP1 show relatively stable device performance compared to spiro‐OMeTAD after aging in ambient air with 30 % relative humidity without encapsulation in the dark. The present results demonstrate that TPA could be an excellent building block to design dopant‐free HTMs for perovskite solar cells and holds promise to replace p‐doped spiro‐OMeTAD, which is important for the fabrication of cost‐effective and stable devices.

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Section: Figuresupporting

confidence: 84%

Efficient, Stable, Dopant‐Free Hole‐Transport Material with a Triphenylamine Core for CH₃NH₃PbI₃ Perovskite Solar Cells

Pan

Liu

et al. 2017

Energy Tech

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“…[58,59,79] Due to the highly branched structures, these molecules showed insignificant aggregation or crystallization in the solid films. The differences between these molecules are the number of branched arms and their conjugation length.…”

Section: Wwwadvancedsciencenewscommentioning

confidence: 99%

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

Zhou

Wen

Gao

2018

Advanced Energy Materials

252

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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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“…[255][256][257][258] We further note that the loss in performance is often related to the use of additives like Li-TFSI, tert-butylpyridine (tBP), and Co-complexes, necessary to oxidize the HTM and achieve high enough conductivities to ensure balanced charge extraction and maximum device performance. [259][260][261] Therefore, several HTMs have been developed that do not require these additives in order to obtain good performance. However, in general, devices without additives show lower PCEs than their counterparts containing the additives.…”

Section: Wwwadvancedsciencenewscommentioning

confidence: 99%

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

Petrus

Schlipf

Cheng

et al. 2017

Advanced Energy Materials

317

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following statement: These materials can be processed from solution and yet exhibit optoelectronic materials properties described in classic solid-state physics textbooks. This unprecedented combination has led to photovoltaic devices that can be processed at room temperature and achieve performance levels similar to industry giant polycrystalline silicon, from a starting point of 3.8% in 2009. [1][2][3][4] The first light-emitting electrochemical cells [5] and diodes [6][7][8] have also been introduced recently, leading to tunable light emission spectra and internal quantum efficiencies exceeding 15%.The road towards these achievements has been marked by a constant improvement of perovskite deposition techniques fueled by our increasing understanding of the crystallization processes. The choice of deposition technique, either from solution or vapor, and the composition and order in which precursor species are applied has a great influence on the crystallization kinetics. Here, one can distinguish one-step methods where the perovskite is formed from a precursor mixture dissolved in a common solution, and two-step methods where the inorganic compound is deposited first and transformed to the perovskite phase later by addition of the organic constituents. [9][10][11] Furthermore, many parameters during processing can have an effect on the crystallization mechanism and consequently on film morphology, such as the choice of solvents, concentrations and processing additives that are often not incorporated into the final product. [11][12][13] We discuss this aspect in Section 2, where we focus our attention on the most commonly employed solution-based techniques. Additionally, as for any new technology trying to displace an incumbent technology, higher efficiencies, lower costs, reproducibility, stability, and sustainability are paramount. In particular, reproducibility has been a major challenge in perovskite solar cells from the beginning: small variations in morphology, like crystal size, film roughness, and pinholes can have detrimental effects on photovoltaic performance. [14] On the other hand, current-voltage measurements often showed a hysteresis that is rarely seen in other photovoltaic technologies. [15] These topics are highlighted in Sections 3 and 4. Finally, in Section 5 we discuss the framework for market introduction, such as cost reduction by choosing low-cost charge transport layers, or how the lifetime of perovskite absorbers can be extended by the choice of materials composition.Hybrid metal halide perovskites have become one of the hottest topics in optoelectronic materials research in recent years. Not only have they surpassed everyone's expectations and achieved similar performance as tried and true polycrystalline silicon photovoltaic devices, but they are also finding applications in a variety of different fields, including lighting. The main advantages of hybrid metal halide perovskites are simple processability, compatible with large-scale solution processing such as roll-to-roll printing, a...

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Dopant‐Free Donor (D)–π–D–π–D Conjugated Hole‐Transport Materials for Efficient and Stable Perovskite Solar Cells

Cited by 84 publications

References 56 publications

Efficient, Stable, Dopant‐Free Hole‐Transport Material with a Triphenylamine Core for CH₃NH₃PbI₃ Perovskite Solar Cells

Efficient, Stable, Dopant‐Free Hole‐Transport Material with a Triphenylamine Core for CH₃NH₃PbI₃ Perovskite Solar Cells

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

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

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Dopant‐Free Donor (D)–π–D–π–D Conjugated Hole‐Transport Materials for Efficient and Stable Perovskite Solar Cells

Cited by 84 publications

References 56 publications

Efficient, Stable, Dopant‐Free Hole‐Transport Material with a Triphenylamine Core for CH3NH3PbI3 Perovskite Solar Cells

Efficient, Stable, Dopant‐Free Hole‐Transport Material with a Triphenylamine Core for CH3NH3PbI3 Perovskite Solar Cells

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

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

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Product

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Efficient, Stable, Dopant‐Free Hole‐Transport Material with a Triphenylamine Core for CH₃NH₃PbI₃ Perovskite Solar Cells

Efficient, Stable, Dopant‐Free Hole‐Transport Material with a Triphenylamine Core for CH₃NH₃PbI₃ Perovskite Solar Cells