High-performance dopant-free conjugated small molecule-based hole-transport materials for perovskite solar cells

Azmi, Randi; Nam, So Youn; Sinaga, Septy; Akbar, Zico Alaia; Lee, Chang Lyoul; Yoon, Sung Cheol; Jung, In Hwan; Jang, Sung‐Yeon

doi:10.1016/j.nanoen.2017.12.002

Cited by 129 publications

(89 citation statements)

References 43 publications

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“…The higher hydrophobicity and lack of additional dopants in mDPA‐DBTP effectively improved the air storage stability of L‐PSCs. The dopant‐free mDPA‐DBTP device retained 81% of its original PCE after 33 days of storage, during which the doped spiro‐OMeTAD devices lost their PCE completely . Although HTMs exhibited a higher PCE than doped spiro‐OMeTAD is very scarce, but there are a promising number of reported small molecule HTMs showed comparable efficiencies.…”

Section: Dopant‐free Hole Transporting Materials For Pscsmentioning

confidence: 99%

Dopant‐Free Hole Transporting Materials for Perovskite Solar Cells

Rezaee

Liu

et al. 2018

Solar RRL

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This article reviews various dopant-free hole transporting materials (HTMs) used in perovskite solar cells (PSCs) in three main categories including inorganic, polymeric, and small molecule HTMs. PSCs have undergone rapid progress, achieving power conversion efficiencies (PCEs) above 22%. With their low production cost and high efficiencies, PSCs are considered promising next-generation solar cell technology. In all developed architectures for PSCs, including planar and mesoscopic with conventional and inverted structures, HTMs play a significant role in determining the photovoltaic performance of PSCs. Using p-type dopants, however, is considered a common strategy to increase the hole conductivity of HTM, which is usually compensated by a more complicated fabrication procedure, higher production costs, and lower stability of PSC. Although several reviews on HTMs have been published, progress on dopant free HTMs needs to be reviewed and analyzed. Here, a review covering most of the published reports on dopantfree HTMs is presented, and the device structure and fabrication method, HTM layer deposition techniques, and the efficiency and the stability of PSCs are addressed during discussions in each main category. Finally, an outlook on stability and PCE growth in PSCs based on dopant-free HTMs is presented.

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Section: Dopant‐free Hole Transporting Materials For Pscsmentioning

confidence: 99%

Dopant‐Free Hole Transporting Materials for Perovskite Solar Cells

Rezaee

Liu

et al. 2018

Solar RRL

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“…As a classic and standard HTM, 2,2′,7,7′‐tetrakis(N,N‐di‐ p ‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) yielded the highest PCE so far of 24.2%, however, it requires doping treatment by oxidants to enhance its hole conductivity, which always inevitably leads to the consequences of long fabrication duration and poor long‐term stability for the PSC devices . As a result, numerous dopant‐free organic substitutes including small molecules and polymers have been developed, and reports of PCE values of over 19% have been frequently issued. Although PCEs of 20.5 and 23.3% were also released, this high efficiency was obtained through optimizing the ETM layer or the perovskite layer, while the HTM itself was earlier designed/employed and reported with a PCE of only 18.3 or 0.52% at its first appearance.…”

Section: Introductionmentioning

confidence: 99%

Side‐Chain Engineering on Dopant‐Free Hole‐Transporting Polymers toward Highly Efficient Perovskite Solar Cells (20.19%)

Zhang

Liu

Wang

et al. 2019

Adv Funct Materials

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A variety of dopant-free hole-transporting materials (HTMs) is developed to serve as alternatives to the typical dopant-treated ones; however, their photovoltaic performance still falls far behind. In this work, the side chain of a polymeric HTM is engineered by partially introducing diethylene glycol (DEG) groups in order to simultaneously optimize the properties of both the bulk of the HTM layer and the HTM/perovskite interface. The intermolecular π-π stacking interaction in the HTM layer is unexpectedly weakened after the incorporation of DEG groups, whereas the lamellar packing interaction is strengthened. A doubled hole mobility is obtained when 3% of the DEG groups replace the original alkyl side chains, and a champion power conversion efficiency (PCE) of 20.19% (certified: 20.10%) is then achieved, which is the first report of values over 20% for dopant-free organic HTMs. The device maintains 92.25% of its initial PCE after storing at ambient atmosphere for 30 d, which should be due to the enhanced hydrophobicity of the HTM film.yielded the highest PCE so far of 24.2%, [1] however, it requires doping treatment by oxidants to enhance its hole conductivity, which always inevitably leads to the consequences of long fabrication duration and poor long-term stability for the PSC devices. [3][4][5] As a result, numerous dopant-free organic substitutes including small molecules and polymers [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] have been developed, and reports of PCE values of over 19% [29,31,45,46] have been frequently issued. Although PCEs of 20.5 [47] and 23.3% [48] were also released, this high efficiency was obtained through optimizing the ETM layer [47] or the perovskite layer, [48] while the HTM itself was earlier designed/ employed and reported with a PCE of only 18.3 [49] or 0.52% [50] at its first appearance. Therefore, strictly speaking there are no dopant-free organic HTMs reported yet to present a PCE of over 20%. Previously, designing of HTMs was mainly focused on the bulky properties of the HTM layer, especially the hole mobilities, and consequently the well-known face-on molecular orientation where the plane of polymer's main chain is parallel or intermolecular π-π stacking direction is perpendicular to the substrate was widely adopted as a criterion when one designs an HTM. [29,[31][32][33]49] Later, the interfaces between the perovskite and HTM layer were paid attention to be modified by small molecules [51][52][53] and polymers, [54,55] so that the defects on the surface and/or in the bulk of the perovskite layer could be passivated, leading to an enhanced photovoltaic performance.

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“…The valence band (VB) edge ( E v ), onset ( E v – E F ) and secondary electron cut off ( E cut‐off ) energy regions in the UPS spectra are shown in Figure a. In the case of UPS, HOMO levels were obtained using the equation HOMO = 21.22– E Cut‐off + ( E V – E F ), while it was associated with the first oxidation potential ( E ox ) in CV (Figure b) . It was found the HOMO level of 2 m F‐X59 from the UPS analysis and CV measurement showed good consistency, both giving a −5.14 eV value (Table ).…”

Section: Resultsmentioning

confidence: 99%

Introduction of Fluorine Into spiro[fluorene‐9,9′‐xanthene]‐Based Hole Transport Material to Obtain Sensitive‐Dopant‐Free, High Efficient and Stable Perovskite Solar Cells

Guo

Yang

et al. 2019

Solar RRL

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Despite the substantial development of efficient hole transporting materials (HTMs) for high‐performance perovskite solar cells (PSCs), optimization of the HTMs to sensitive‐dopant‐free HTMs for high efficient PSCs with prominent stability have rarely been reported. Herein, a low‐cost fluorinated spiro[fluorene‐9,9′‐xanthene] based HTM termed 2mF‐X59 is designed and synthesized. In comparison with its reported nonfluorinated counterpart X59, 2mF‐X59 shows lowered highest occupied molecular orbital (HOMO) level, improved hole mobility, and hydrophobicity. Aided by 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) to further lower the HOMO level of 2mF‐X59 and improve its hole transfer, the optimized 2mF‐X59 based PSCs show a maximum power conversion efficiency (PCE) of 18.13% without the use of any sensitive‐dopants (e.g., lithium salt/4‐tert‐butylpyridine), which is comparable to the Spiro‐OMeTAD based PSCs (18.22%) with sensitive dopants. More importantly, the sensitive‐dopant‐free 2mF‐X59 based PSCs maintain 95% of their initial performance for more than 500 h under air exposure, showing much better long‐term stability than control PSCs based on Spiro‐OMeTAD with sensitive dopanst. This is the first case that a sensitive‐dopant‐free HTM is demonstrated in PSCs with a high PCE (>18%) and good stability by optimizing the literature HTM. This work could pave a new way to develop low‐cost sensitive‐dopant‐free HTMs for highly efficient and stable PSCs for practical applications.

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High-performance dopant-free conjugated small molecule-based hole-transport materials for perovskite solar cells

Cited by 129 publications

References 43 publications

Dopant‐Free Hole Transporting Materials for Perovskite Solar Cells

Dopant‐Free Hole Transporting Materials for Perovskite Solar Cells

Side‐Chain Engineering on Dopant‐Free Hole‐Transporting Polymers toward Highly Efficient Perovskite Solar Cells (20.19%)

Introduction of Fluorine Into spiro[fluorene‐9,9′‐xanthene]‐Based Hole Transport Material to Obtain Sensitive‐Dopant‐Free, High Efficient and Stable Perovskite Solar Cells

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