Chen Weijie

Publication date: 18 May 2022

Source: Joule, Volume 6, Issue 5

Author(s): Ryan M. France, John F. Geisz, Tao Song, Waldo Olavarria, Michelle Young, Alan Kibbler, Myles A. Steiner

The construction of a superhydrophilic bionic interface layer (Bio-IL) significantly suppresses the coffee-ring effect during printing of large-area perovskite films via regulating the nucleation rate (υ_N) and radial transport rate (υ_RT) of the perovskite precursor, which induces a homogeneous large-area flexible perovskite film and high-performance inverted flexible perovskite solar cells with an efficiency of 21.08%.

Abstract

The inhomogeneity, poor interfacial contact, and pinholes caused by the coffee-ring effect severely affect the printing reliability of flexible perovskite solar cells (PSCs). Herein, inspired by the bio-glue of barnacles, a bionic interface layer (Bio-IL) of NiO _x /levodopa is introduced to suppress the coffee-ring effect during printing perovskite modules. The coordination effect of the sticky functional groups in Bio-IL can pin the three-phase contact line and restrain the transport of perovskite colloidal particles during the printing and evaporation process. Moreover, the sedimentation rate of perovskite precursor is accelerated due to the electrostatic attraction and rapid volatilization from an extraordinary wettability. The superhydrophilic Bio-IL affords an even spread over a large-area substrate, which boosts a complete and uniform liquid film for heterogeneous nucleation as well as crystallization. Perovskite films on different large-area substrates with negligible coffee-ring effect are printed. Consequently, inverted flexible PSCs and perovskite solar modules achieve a high efficiency of 21.08% and 16.87%, respectively. This strategy ensures a highly reliable reproducibility of printing PSCs with a near 90% yield rate.

The a-Si:H-based triple-junction p type/intrinsic/n type solar cells are built on c-Si nanowires. They deliver 2.05 V open-circuit voltage, 3.8 mA cm⁻² current density, and 0.57 fill factor, resulting in a 4.4% energy conversion efficiency.

When solar cells are used as the photoanode for direct water splitting, the output voltage required typically exceeds that of a single-junction photovoltaic device. Toward this application, in this work, triple radial junction silicon nanowire (3RJ SiNW) solar cells are fabricated via a plasma-assisted vapor-liquid-solid method using hydrogenated amorphous silicon (a-Si:H) for all the absorber layers, as well as for the doped ones. A high open-circuit voltage (V _OC) of 2.05 V, short-circuit current density (J _SC) of 3.8 mA cm⁻², and power conversion efficiency of 4.4% are obtained for solar cells with areas of 0.03 cm² by optimizing the density of SiNWs grown on ZnO:Al/Ag/Corning glass substrates. For lower-efficiency devices, however, V _OC values as high as 2.2 V are consistently achieved. At these higher voltages, large variations in J _SC are observed, attributed to small local variations in SiNW density. Herein, for the first time, the excellent potential of 3D radial junction solar cells for applications requiring high voltages and high surface areas, such as water splitting is demonstrated.

Chemical instability within conventional hybrid perovskites is addressed using inorganic CsPbI₃-based systems. A novel γ-CsPb_{1− x} Tb _x (IBr)₃ perovskite is fabricated with the help of bulk and surface passivation methods, the combination of which ensures ambient-processed and stable inorganic lead halide perovskite solar cells that produce 19% power conversion efficiency with >90% thermal-stability over 300 h at 85 °C.

Abstract

Realizing photoactive and thermodynamically stable all-inorganic perovskite solar cells (PSCs) remains a challenging task within halide perovskite photovoltaic (PV) research. Here, a dual strategy for realizing efficient inorganic mixed halide perovskite PV devices based on a terbium-doped solar absorber, that is, CsPb_{1− x} Tb _x I₂Br, is reported, which undertakes a bulk and surface passivation treatment in the form of CsPb_{1− x} Tb _x I₂Br quantum dots, to maintain a photoactive γ-phase under ambient conditions and with significantly improved operational stability. Devices fabricated from these air-processed perovskite thin films exhibit an air-stable power conversion efficiency (PCE) that reaches 17.51% (small-area devices) with negligible hysteresis and maintains >90% of the initial efficiency when operating for 600 h under harsh environmental conditions, stemming from the combined effects of the dual-protection strategy. This approach is further examined within large-area PSC modules (19.8 cm² active area) to realize 10.94% PCE and >30 days ambient stability, as well as within low-bandgap γ-CsPb_0.95Tb_0.05I_2.5Br_0.5 (E _g = 1.73 eV) materials, yielding 19.01% (18.43% certified) PCE.

[2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2P) is introduced to modify the surface of the hole-transport layer (HTL). 2P benefits the perovskite growth and interfacial contact. Moreover, 2P-modified HTL shows better energy-level alignment with perovskite. The 2P-incorporated inverted perovskite solar cell delivers a high efficiency of 22.17% and keeps stable under ambient atmosphere (RH: ≈30–40%) without encapsulation for 7200 h.

Abstract

Inverted perovskite solar cells (PSCs) have received widespread attention due to their facile fabrication and wide applications. However, their power conversion efficiency (PCE) is reported lower than that of regular PSCs because of the undesirable interfacial contact between perovskite and the hydrophobic hole transport layer (HTL). Here, an interface regulation strategy is proposed to overcome this limitation. A small molecule ([2-(9H-carbazol-9-yl) ethyl] phosphonic acid, abbreviated as 2P), composed of carbazole and phosphonic acid groups, is inserted between perovskite and HTL. Morphological characterization and theoretical calculation reveal that perovskite bonds stronger on 2P-modified HTL than on pristine HTL. The improved interfacial contact facilitates hole extraction and retards degradation. Upon the incorporation of 2P, inverted PSCs deliver a high PCE of over 22% with superior stability, keeping 84.6% of initial efficiency after 7200 h storage under an ambient atmosphere with a relative humidity of ≈30–40%. This strategy provides a simple and efficient way to boost the performance of inverted PSCs.

Publication date: August 2022

Source: Applied Materials Today, Volume 28

Author(s): Yue Wang, Deli Li, Lingfeng Chao, Tingting Niu, Yonghua Chen, Wei Huang

Publication date: August 2022

Source: Nano Energy, Volume 99

Author(s): Bin Liu, Yuqi Wang, Yanjie Wu, Zhongqi Liu, Shuhang Bian, Yuhong Zhang, Le Liu, Xinmeng Zhuang, Shuainan Liu, Zhichong Shi, Xue Bai, Lin Xu, Donglei Zhou, Biao Dong, Hongwei Song

Publication date: 15 June 2022

Source: Joule, Volume 6, Issue 6

Author(s): Xiaoyu Yang, Qiuyang Li, Yifan Zheng, Deying Luo, Yuzhuo Zhang, Yongguang Tu, Lichen Zhao, Yanju Wang, Fan Xu, Qihuang Gong, Rui Zhu

Methylammonium chloride and formamide as additives are developed for highly efficient and reproducible wide-bandgap perovskite solar cells in ambient air processing. Due to overcoming drawbacks resulting from processing at ambient air via additives, perovskite solar cells with well-controlled film morphology and passivation exhibit superior photostability and improved power conversion efficiency compared with the pristine film.

Perovskite solar cells (PSCs) have emerged as the next generation of solar cells because of the promising nature of creating tandem solar cells with Si photovoltaics. Wide-bandgap PSCs are developed to improve the power conversion efficiency (PCE) and stability of tandem devices. For the mass production of tandem solar cells, not only is a limitation of scalable coating a critical factor, but uncontrollable grain growth in ambient air impedes commercialization. Serious differences in morphology depending on the experimental environment are found. In the ambient air processing system, severe wrinkles and voids resulting in deteriorated photovoltaic performance are found as compared with those in N₂ condition. It is suggested that humidity in the air plays a crucial role in the remaining perovskite intermediate phase and the rate of solvent evaporation during the spin-coating procedure. Herein, void- and wrinkle-free perovskite films using methyl ammonium chloride and formamide are fabricated, thus leading to efficient PSCs with a PCE of 20.6%. Furthermore, newly designed perovskite films to blade coating for large-area fabrication as well as to semitransparent PSCs for a four-terminal silicon/perovskite tandem solar cell with a PCE of 25.2% are applied.

First-principles density functional theory calculations unveil the important but overlooked role of hydrogen impurities in nonradiative recombination losses in the solar cell material CsPbI₃. Iodine-moderate synthesis conditions can effectively reduce the density of the detrimental hydrogen ions, which is critical for the future design of CsPbI₃-based solar cells with higher performance.

All-inorganic halide perovskites have thus far exhibited better thermal stability but lower power conversion efficiency (PCE), compared with their organic–inorganic hybrid counterparts. The experimentally observed nonradiative recombination loss is commonly attributed to the prevalence of native deep defects, yet the exact microscopic origin remains elusive. Based on density functional theory calculations, it is demonstrated that hydrogen impurities may incorporate in the prototypical all-inorganic perovskite CsPbI₃ with a high density and serve as a new source of efficient nonradiative recombination centers. The resultant nonradiative efficiency loss can be significantly higher than those induced by native deep defects, namely interstitials I i and antisites I Cs , contributing to the subdued performance of the CsPbI₃-based devices. Furthermore, it is proposed that the iodine-moderate growth conditions can effectively reduce the detrimental hydrogen ions. These results highlight the impact of unintentionally incorporated impurities and offer insights into the optimal synthetic route and practical operating protocols in the field of all-inorganic perovskite solar cells.

Highly dispersed NiO_x nanocrystals with tunable size and energy levels have been successfully synthesized and applied as hole transport layer for perovskite solar cells. Power conversion efficiency approaching 23% is achieved, together with excellent device stability under ultraviolet irradiance.

Abstract

Solution-processed nickel oxide nanocrystals (NiO_x NCs) ink can be facilely applied to deposit NiO_x thin films as the hole transport layer (HTL) for perovskite solar cells (PSCs). Both the efficiency and stability of the corresponding PSCs depend significantly on the size and the energy levels of the as-synthesized NiO_x NCs; however, previous studies have shown that these two aspects can be hardly controlled synchronously to maximize the device performance. Herein, a novel synthesis of highly dispersed NiO_x NCs is demonstrated by employing tetraalkylammonium hydroxides (TAAOHs, alkyl = methyl, ethyl, propyl, butyl) as precipitating bases, where the varied alkyl chain lengths of TAAOHs enable the size control of the NiO_x NCs and the subsequent altering of their Ni³⁺ contents, leading to tunable energy levels of the NiO_x thin films. With the longest butyl chain, the smallest crystal size and the optimal energy level alignment at the NiO_x/perovskite interface are achieved. After further passivating the detrimental Ni³⁺ species on the surface of NiO_x HTL, a remarkable power conversion efficiency (PCE) approaching 23% is obtained, which is one of the highest PCEs reported for NiO_x-based inverted PSCs. Furthermore, the unencapsulated device exhibits excellent ultraviolet stability, which maintains ≈87% of its PCE after 200 h exposure.

In order to improve the performance of flexible perovskite solar cells (F-PSCs), this work proposes the inner encapsulation strategy to heal the surface defects of perovskite film and prevent moisture invasion. F-PSCs with high efficiency in outdoor/indoor scenes and considerable long-term stability are achieved. This work sheds new light on fabricating the highly-efficient and stable F-PSCs.

Abstract

Flexible perovskite solar cells possess huge application potential in both outdoor (sunlight) and indoor scenes (artificial low light) owing to their high optoelectronic conversion efficiency and agile integration advantages. In order to further establish their feasibility to meet multi-scenario applications, here a facile “internal packaging” interface strategy is developed, where a selective light-cured cross-linking molecule is leveraged to effectively heal the interface defects over perovskite films. Moreover, the cross-linked interfacial layer can act as an airtight “protective wall”, preventing the device from water and oxygen corrosion and lead leakage. The flexible devices aided by this strategy show considerable performance ranging from small size to scalable modules (20.86%-0.07 cm², 16.75%-24 cm²). More importantly, the optimal devices yield excellent moisture resistance, light soaking resistance, and lead leakage prevention stability. Based on the common light source environment of indoor scenes, the excellence of flexible modules (30.73% under white light-emitting diode (LED), 26.48% under yellow LED) is further validated. It is expected that this gentle strategy can underline simultaneous promoting of the efficiency and stability of flexible perovskite modules, thereby accelerating the application of flexible perovskite in advanced industrial fields.

Dual interface coupling is established by defective multi-walled carbon nanotube to well tune the charge transfer kinetics regarding hole transport layer (HTL) itself at molecular level and the interface between HTL and carbon electrode at nanometer scale. High power conversion efficiency (PCEs) up to 22.07% (with a certified PCE of 21.9%) and excellent operational stability are achieved.

Abstract

Suffering from sluggish charge transfer kinetics, carbon-based perovskite solar cells (C-PSCs) lag far behind the Ag/Au-based normal PSCs in power conversion efficiency (PCE). Herein, the use of defective multi-walled CNT (D-MWCNT) is demonstrated to tune the charge transfer kinetics regarding hole transport layer (HTL) and the interface between HTL and carbon electrode. Benefiting from the electrostatic dipole moment interaction between the terminal oxygen-containing groups of D-MWCNT and 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene, an interface coupling at molecular level is established and in turn, allows rapid charge transfer by edge effect induced electron redistribution and 1D hyper-channels. Meanwhile, a seamless connection between HTL and carbon electrode is achieved in a novel modular C-PSCs due to D-MWCNT induced interface coupling with graphene at nanometer scale. Based on this strategy, high PCEs up to 22.07% (with a certified record PCE of 21.9% to date for C-PSCs) and excellent operational stability have been achieved.

Nature Energy, Published online: 12 May 2022; doi:10.1038/s41560-022-01018-5

The effects of additive engineering on Cs_0.1FA_0.9PbI₃ perovskites using Sr²⁺ and Ca²⁺ are investigated. The performance of CsFA-based perovskite solar cells (PSCs) is remarkably improved by 0.5% additive concentration. It is also reported that the additives lead to a significant decrease in the hysteresis in PSCs due to metal halide passivation at grain boundaries.

Organic–inorganic lead halide perovskite solar cells are regarded as one of the most promising technologies for the next generation of photovoltaics due to their high power conversion efficiency (PCE) and simple solution manufacturing. Among the different compositions, the formamidinium lead iodide (FAPbI₃) photoactive phase has a bandgap of 1.4 eV, which enables the corresponding higher PCEs according to the Shockley–Queisser limit. However, the photoactive crystal phase of FAPbI₃ is not stable at room temperature. The most high-performing compositions to date have reduced this problem by incorporating the methylammonium (MA) cation into the FAPbI₃ composition, although MA has poor stability at high temperatures and in humid environments, which can limit the lifetime of FA _x MA_1−x PbI₃ films. Cs _x FA_1−x PbI₃ perovskites are also explored, but despite better stability they still lag in performance. Herein, the additive engineering of MA-free organic−inorganic lead halide perovskites using divalent cations Sr²⁺ and Ca²⁺to enhance the performances of Cs _x FA_1−x PbI₃ perovskite compositions is explored. It is revealed that the addition of up to 0.5% of Sr²⁺ and Ca²⁺ leads to improvements in morphology and reduction in microstrain. The structural improvements observed correlate with improved solar cell performances at low additive concentrations.

A multifunctional amino alcohol is selected as an additive to passivate the perovskite layer in perovskite solar cells. The BHF additive stabilizes the interface structure and improves the device stability. Herein, a better understanding of the function of BHF additives in perovskite materials and their effect on device performance is provided.

The interfacial or bulk defects of the perovskite layer are important factors that affect the stability and photoelectric conversion efficiency of perovskite solar cells (PSCs). Herein, a multifunctional amino alcohol, 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoro propane (BHF), C₁₅H₁₂F₆N₂O₂, is used as an additive of the active layer in p–i–n organic–inorganic halide perovskite solar cells. The BHF additive passivates perovskite predominately at grain boundaries. This additive leads to a vertically aligned crystal grain and reduced defect densities. The BHF-treated perovskite films show suppressed nonradiative recombination with enhanced photoluminescence, longer carrier lifetimes, and reduced ionic migration. The device doped with 1 mg mL⁻¹ BHF is able to improve power conversion efficiency to 20.30% (from 16.83% of the control), mainly due to the improvement of open-circuit voltage. In addition, BHF passivation generates a more stable perovskite structure, resulting in improved operational stability of the PSCs.

An efficient hole selection interface with reduced recombination loss is achieved through co-assembly of a structurally engineered hole-selective self-assembled monolayer (SAM) and an ammonium passivator, with which a champion power conversion efficiency (PCE) of 23.59 % and improved device stability are accomplished in inverted perovskite solar cells (PSCs).

Abstract

Self-assembled monolayers (SAMs) have been widely employed as an effective way to modify interfaces of electronic/optoelectronic devices. To achieve a good control of the growth and molecular functionality of SAMs, we develop a co-assembled monolayer (co-SAM) for obtaining efficient hole selection and suppressed recombination at the hole-selective interface in inverted perovskite solar cells (PSCs). By engineering the position of methoxy substituents, an aligned energy level and favorable dipole moment can be obtained in our newly synthesized SAM, ((2,7-dimethoxy-9H-carbazol-9-yl) methyl) phosphonic acid (DC-PA). An alkyl ammonium containing SAM is co-assembled to further optimize the surface functionalization and interaction with perovskite layer on top. A champion device with an excellent power conversion efficiency (PCE) of 23.59 % and improved device stability are achieved. This work demonstrates the advantage of using co-SAM in improving performance and stability of PSCs.

Solar Water Oxidation

In article number 2103698, James R. Durrant and co-workers design organic bulk-heterojunction photoanodes with a polymer overlayer for solar water oxidation. The additional polymer layer improves underwater operational stability and suppresses recombination losses. Employing these photoanodes, solar water oxidation under near-infrared irradiation is demonstrated with an incident photon-to-current efficiency up to 25% at 770 nm illumination.