Role of 4- tert -Butylpyridine as a Hole Transport Layer Morphological Controller in Perovskite Solar Cells

104

To date, the most efficient perovskite solar cells (PSCs) employ an n–i–p device architecture that uses a 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) hole‐transporting material (HTM), which achieves optimum conductivity with the addition of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and air exposure. However, this additive along with its oxidation process leads to poor reproducibility and is detrimental to stability. Herein, a dicationic salt spiro‐OMeTAD(TFSI)2, is employed as an effective p‐dopant to achieve power conversion efficiencies of 19.3% and 18.3% (apertures of 0.16 and 1.00 cm2) with excellent reproducibility in the absence of LiTFSI and air exposure. As far as it is known, these are the highest‐performing n–i–p PSCs without LiTFSI or air exposure. Comprehensive analysis demonstrates that precise control of the proportion of [spiro‐OMeTAD]+ directly provides high conductivity in HTM films with low series resistance, fast hole extraction, and lower interfacial charge recombination. Moreover, the spiro‐OMeTAD(TFSI)2‐doped devices show improved stability, benefitting from well‐retained HTM morphology without forming aggregates or voids when tested under an ambient atmosphere. A facile approach is presented to fabricate highly efficient PSCs by replacing LiTFSI with spiro‐OMeTAD(TFSI)2. Furthermore, this study provides an insight into the relationship between device performance and the HTM doping level.

Section: Resultsmentioning

confidence: 99%

LiTFSI‐Free Spiro‐OMeTAD‐Based Perovskite Solar Cells with Power Conversion Efficiencies Exceeding 19%

Tan

Raga

Chesman

et al. 2019

104

“…[19] Adv. [9] The perovskite crystals further degraded after 30 d. However, there are almost no "pits" formed on the XPP-based film after 8 d and the perovskite crystals were also protected. 2017, 7, 1700683 Scanning electron microscopy (SEM) was used to investigate the top view of the HTL, as shown in Figure 6a.…”

Section: Resultsmentioning

confidence: 98%

“…[8] Most recently, Meng and co-workers demonstrated that tBP also acted as a morphology controller for the HTMs to significantly improve the uniformity of the HTL and avoided the aggregation of the lithium salt (typically, Li-TFSI). [9] However, tBP also induced instability of the PVSC device because of its relatively low boiling point (196 °C), which is easily evaporated during device fabrication and long-term storage. [10] Han and co-workers further confirmed that tBP tends to corrode perovskite to form a new complex with PbI 2 , leading to chemical decomposition of the perovskite and poor charge transport between the perovskite and HTL.…”

mentioning

confidence: 99%

4‐Tert‐butylpyridine Free Organic Hole Transporting Materials for Stable and Efficient Planar Perovskite Solar Cells

Bai

Zhu

Zhang

et al. 2017

125

4‐Tert‐butylpyridine (tBP) is an important additive in triarylamine‐based organic hole‐transporting materials (HTMs) for improving the efficiency and steady‐state performance of perovskite solar cells (PVSCs). However, the low boiling point of tBP (196 °C) significantly affects the long‐term stability and device performance of PVSCs. Herein, the design and synthesis of a series of covalently linked Spiro[fluorene‐9,9′‐xanthene] (SFX)‐based organic HTMs and pyridine derivatives to realize efficient and stable planar PVSCs are reported. One of the tailored HTMs, N2,N2,N7,N7‐tetrakis(4‐methoxyphenyl)‐3′,6′‐bis(pyridin‐4‐ylmethoxy) spiro[fluorene‐9,9′‐xanthene]‐2,7‐diamine (XPP) with two para‐position substituted pyridines that immobilized on the SFX core unit shows a high power conversion efficiency (PCE) of 17.2% in planar CH3NH3PbI3‐based PVSCs under 100 mW cm−2 AM 1.5G solar illumination, which is much higher than the efficiency of 5.5% that using the well‐known 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxy‐phenyl‐amine)9,9′‐spirobifluorene (Spiro‐OMeTAD) as HTM (without tBP) under the same condition. Most importantly, the pyridine‐functionalized HTM‐based PVSCs without tBP as additive show much better long‐term stability than that of the state‐of‐the‐art HTM Spiro‐OMeTAD‐based solar cells that containing tBP as additive. This is the first case that the tBP‐free HTMs are demonstrated in PVSCs with high PCEs and good stability. It paves the way to develop highly efficient and stable tBP‐free HTMs for PVSCs toward commercial applications.

“…Following this Element maps suggest that perovskite grain boundaries are filled with PBCM in the assisted growth method, whereas PCBM and perovskite are well separated in the conventional method. [48] Copyright 2016, American Chemical Society. [24] Copyright 2016, Royal Society of Chemistry.…”

Section: Electron Energy-loss Spectroscopymentioning

confidence: 99%

Imaging and Mapping Characterization Tools for Perovskite Solar Cells

Hidalgo

Castro‐Méndez

Correa‐Baena

2019

define the perovskite structure, decreases below 0.8 and orthorhombic, rhombohedral, or tetragonal structures tend to form. For large A-cations, layered 2D [3] and 1D [4] chain structures can be formed, e.g., Ruddlesden-Popper, Aurivillius, and Dion-Jacobson phases. Both 3D and 2D perovskites have gained the attention of the solar cell community.Lead halide perovskites are outstanding semiconductors with impressive optoelectronic properties, such as high absorption coefficient, tunable band gap, and long charge carrier lifetimes. Despite having such impressive properties, there is still a need for deeper understanding of the degradation mechanisms of the perovskite materials in order to make PSCs viable for outdoor applications and commercialization. [5,6] Currently, a major challenge facing perovskites is their long-term stability, due to their sensitivity to temperature, moisture, oxygen, and ultraviolet (UV) light. [6] Furthermore, chemical and electronic stability, compositional, and crystal homogeneity in the absorber layer of PSCs are parameters that allow us to understand and ensure the maximum PCE and long-term durability of the devices.Imaging and mapping characterization techniques allow researchers to obtain insights of the nano-and microscale features related to their chemical and electronic properties, which in turn limit PSC performance and long-term durability. This review will focus on the progress of the imaging and mapping techniques that have been used understanding and designing perovskite materials. This comprehensive review will span from basic morphology characterization methods, such as scanning electron microscopy (SEM) to advanced, synchrotron-based characterization using X-ray microscopy, such as X-ray fluorescence for compositional mapping, and X-ray beam induced current (XBIC) for electric performance mapping. Different imaging and mapping tools allow for correlations of different physical, chemical, optical and electrical features in space and time. These characterization techniques have helped explain phenomena that govern perovskite materials, including chemical and electrical properties and how they relate to solar cell performance. The following table summarizes the different imaging and mapping characterization techniques and their use for PSCs research.Perovskite solar cells (PSCs) have attracted much attention as efficiencies have gone beyond 24%. To achieve these impressive numbers, the PSC scientific community is working to improve the perovskite optoelectronic properties. Imaging and mapping characterization techniques have been widely used to understand the fundamental properties that allow lead halide perovskites to achieve high performance. In this review, these techniques are evaluated, from simple tools, such as electron microscopy, to more complex systems that include atomic force microscopy, synchrotron-based X-ray mapping, and ultrafast and photoluminescence mapping. These tools have helped understand lead halide perovskites and their impressive optoelectronic prope...