Additive Engineering for Efficient and Stable Perovskite Solar Cells

In this work, a rational design and construction of porous spherical NiO@NiMoO4 wrapped with PPy was reported for the application of high-performance supercapacitor (SC). The results show that the NiMoO4 modification changes the morphology of NiO, and the hollow internal morphology combined with porous outer shell of NiO@NiMoO4 and NiO@NiMoO4@PPy hybrids shows an increased specific surface area (SSA), and then promotes the transfer of ions and electrons. The shell of NiMoO4 and PPy with high electronic conductivity decreases the charge-transfer reaction resistance of NiO, and then improves the electrochemical kinetics of NiO. At 20 A g−1, the initial capacitances of NiO, NiMoO4, NiO@NiMoO4 and NiO@NiMoO4@PPy are 456.0, 803.2, 764.4 and 941.6 F g−1, respectively. After 10,000 cycles, the corresponding capacitances are 346.8, 510.8, 641.2 and 904.8 F g−1, respectively. Especially, the initial capacitance of NiO@NiMoO4@PPy is 850.2 F g−1, and remains 655.2 F g−1 with a high retention of 77.1% at 30 A g−1 even after 30,000 cycles. The calculation result based on density function theory shows that the much stronger Mo-O bonds are crucial for stabilizing the NiO@NiMoO4 composite, resulting in a good cycling stability of these materials.

Porous spherical NiO@NiMoO4@PPy nanoarchitectures as advanced electrochemical pseudocapacitor materials

Organic semiconductors have become essential parts of thin-film electronic devices, particularly as hole transport layers (HTLs) in perovskite solar cells (PSCs) where they represent one of the major bottlenecks to further enhancements in both device stability and efficiency. Small molecule 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) and polymer poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) are two of the first successful HTLs used in PSCs, and have remained at the forefront of developing high efficiency devices for almost a decade. Since their first application, many investigations into the properties of spiro-OMeTAD and PTAA have contributed to a growing understanding of the mechanisms that enable their success as HTLs. This review summarizes and discusses the key electronic and morphological properties, doping strategies and mechanisms, and degradation pathways of both spiro-OMeTAD and PTAA. A critical comparison between the two materials is provided, highlighting both the similarities which explain their enduring popularity as well as key differences in electrical and morphological properties. From this analysis emerges an improved understanding of the fundamental properties that enable the persistent success of HTL materials, which are found to include not only hole conductivity, band gap, and morphology, but also interactions with dopants, the perovskite, and environmental stressors. The knowledge about these properties, which are critically summarized in this review, is also applicable to the many other types of organic electronic devices now employing spiro-OMeTAD and PTAA. A detailed examination of the properties of materials reveals a clear set of guiding principles for the development of future generation HTLs. Applying these design strategies to produce more advanced HTLs will be essential to further improve the stability, efficiency, and commercialization of PSCs.

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Lessons learned from spiro-OMeTAD and PTAA in perovskite solar cells

3D perovskite solar cells (PSCs) have shown great promise for use in next-generation photovoltaic devices. However, some challenges need to be addressed before their commercial production, such as enormous defects formed on the surface, which result in severe SRH recombination, and inadequate material interplay between the composition, leading to thermal-, moisture-, and light-induced degradation. 2D perovskites, in which the organic layer functions as a protective barrier to block the erosion of moisture or ions, have recently emerged and attracted increasing attention because they exhibit significant robustness. Inspired by this, surface passivation by employing 2D perovskites deposited on the top of 3D counterparts has triggered a new wave of research to simultaneously achieve higher efficiency and stability. Herein, we exploited a vast amount of literature to comprehensively summarize the recent progress on 2D/3D heterostructure PSCs using surface passivation. The review begins with an introduction of the crystal structure, followed by the advantages of the combination of 2D and 3D perovskites. Then, the surface passivation strategies, optoelectronic properties, enhanced stability, and photovoltaic performance of 2D/3D PSCs are systematically discussed. Finally, the perspectives of passivation techniques using 2D perovskites to offer insight into further improved photovoltaic performance in the future are proposed. 

Surface Passivation Using 2D Perovskites toward Efficient and Stable Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells (PSCs) have made unprecedented progress in the past ten years, the power conversion efficiency of which increased from 3.8% in 2009 to 25.5% in 2020. The choice of hole transport layers (HTLs) is a key factor for achieving efficient and stable PSCs. Recently, 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) has been proven to be the most suitable small molecule HTL material in n–i–p PSCs. However, the conductivity and hole mobility of spiro-OMeTAD are dependent on the dopants. Bis(trifluoromethane)sulfonamide lithium salt (LiTFSI) and 4-tert-butylpyridine (TBP) have become the standard HTL dopants to improve the charge transport properties of n–i–p PSCs. Both of these two dopants are effective but have a negative impact on the device stability (induced by ion migration, hygroscopicity, and corrosiveness). In response, lots of efforts have been devoted to the development of alternative and new dopants. In this review, the influence of different doping strategies and corresponding doping mechanisms on device performance and stability was mainly discussed. The stability issues of doped spiro-OMeTAD based PSCs were also described. Finally, we proposed some possible future research goals for dopants based on these existing results to obtain long-lasting and high-efficiency PSCs.

Strategies of modifying spiro-OMeTAD materials for perovskite solar cells: a review

A high-performance pseudocapacitive electrode material for supercapacitors based on the unique NiMoO4/NiO nanoflowers

Efficient and Stable 2D@3D/2D Perovskite Solar Cells Based on Dual Optimization of Grain Boundary and Interface

Spiro-OMeTAD as a hole-transport material (HTM) plays a crucial role in the photovoltaic performance and stability of perovskite solar cells (PSCs). However, the inferior conductivity and mediocre hole-mobility of unoxidized spiro-OMeTAD limit its function. In order to improve the functional properties of HTMs, we develop a new kind of dopant, vanadic oxide (V2O5) in place of the traditional oxygen in the presence of a lithium salt. V2O5 with strong redox potential can rapidly oxidize spiro-OMeTAD, which effectively improves the hole-transport properties and adjusts the energy level of the HTM. Consequently, the champion PSC based on the V2O5-doped HTM achieves a power conversion efficiency of 20.5%, while the device without V2O5 doping exhibits an efficiency of 18.1% under the same test conditions. Meanwhile, owing to the reduction of trap state density and the band gap adjustment by V2O5 doping the hysteresis of devices is effectively suppressed and the stability is improved. The facile and inexpensive treatment and obvious performance improvement render the present finding very promising.

Zeyu Song

Papers

A high-performance pseudocapacitive electrode material for supercapacitors based on the unique NiMoO4/NiO nanoflowers

Efficient and Stable 2D@3D/2D Perovskite Solar Cells Based on Dual Optimization of Grain Boundary and Interface

High performance and stable perovskite solar cells using vanadic oxide as a dopant for spiro-OMeTAD

Excellent quinoline additive in perovskite toward to efficient and stable perovskite solar cells

Application of CoV-LDH nano-flower in asymmetric supercapacitors with high electrochemical properties