Fabrication and photoluminescent properties of heteroepitaxial ZnO/Zn0.8Mg0.2O coaxial nanorod heterostructures

ZnO/Zn0.8Mg0.2O coaxial nanorod heterostructures were prepared by employing catalyst-free metal-organic vapor-phase epitaxy, and their structural and photoluminescent (PL) properties were investigated using transmission electron microscopy (TEM) and temperature-dependent PL spectroscopy. TEM images show that ZnO/Zn0.8Mg0.2O layers were epitaxially grown on the entire surfaces of the ZnO nanorods and the ZnO nanorod diameters as a core material were as small as 9 +/- 2 nm. A dominant PL peak was observed at 3.316 eV, from room-temperature PL spectra of ZnO/Zn0.8Mg0.2O coaxial nanorod heterostructures with ZnO core diameters of 9 nm, indicating a PL blue shift of 30 meV, which resulted from a quantum confinement effect along the radial direction in ZnO nanorods. Furthermore, temperature-dependent PL properties of the coaxial nanorod heterostructures were investigated, showing much higher PL intensity for the coaxial nanorod heterostructures than that of bare ZnO nanorods at room temperature. The origin of the enhanced PL intensity and reduced thermal quenching for the coaxial nanorod heterostructures is also discussed.     

Copper-copper iodide hybrid nanostructure as hole transport material for efficient and stable inverted perovskite solar cells

A CuI coated Cu hybrid nanostructure by partial iodation of Cu nanowires was used as hole transport material(HTM) to enhance the charge transfer in inverted perovskite solar cells(PSCs). The outer CuI achieved efficient charge extraction, and the inner copper facilitated the extracted charges to be rapidly transferred, further improving the overall cell performance. Furthermore,we employed a mixture of [6,6]-phenyl-C71-butyric acid methyl ester(PCBM) and ZnO nanoparticles as electron transport material(ETM) to achieve the fabrication of stable PSCs. The best efficiency was up to 18.8%. This work represents a fundamental clue for the design of efficient and stable PSCs using the chemical in-situ construction strategy for HTM and integration of PCBM and ZnO as ETM.     

钙钛矿太阳能电池电子传输层的制备及应用

目前,有机-无机杂化钙钛矿太阳能电池(PSC)的器件效率已经超过25％.电子传输层作为PSC中的重要组成部分在提取和传输光生电子,阻挡空穴,修饰界面,调节界面能级和减少电荷复合等方面起着关键作用.无机n型材料,例如TiO2、ZnO、SnO2和其他金属氧化物材料具有成本低和稳定性好的特点,经常在传统PSC中被用作电子传输...     

Enhanced ultraviolet emission from ZnS-coated ZnO nanowires fabricated by self-assembling method

A simple chemical route for ZnS-coated ZnO nanowires with preferential (002) orientation is reported. Sodium sulfide and zinc nitrate were employed to supply S and Zn atoms at 60 degrees C to form ZnS-coated ZnO nanowires structures. Electron diffraction measurement shows that the ZnO/ZnS core-shell nanostructure is single crystalline. Interesting features are found in the photoluminescence (PL) spectra of ZnS-coated ZnO nanostructures. After coating, the UV emission of nanorods is dramatically enhanced at the expense of the green emission. The core/shell structure with higher band gap shell material and reduced surface states should be responsible for this PL enhancement.     

反式钙钛矿电池超薄空穴传输层研究进展

空穴传输层(HTLs)厚度对反式钙钛矿太阳能电池(PSCs)性能具有重大影响,因其显著影响太阳光透过和HTLs的空穴传输性能。几个纳米至十几个纳米厚度的超薄HTLs在减少伴生吸收、电荷传输损失和材料消耗等方面具有明显优势。目前,有许多成熟的制备超薄无机HTLs的方法,并在反式和叠层PSCs中得到广泛研究与应用。最近,一些关于有机超薄HTLs的新型制备方法也展现出良好的性能并逐渐引起相关领域研究者关注。在此,本文主要总结反式PSCs中超薄HTLs的研究进展与应用,关注其未来发展的挑战和方向,为该领域进一步的研究提供参考。     

SnO2表面卤化提高钙钛矿太阳能电池光伏性能

钙钛矿太阳能电池(PSCs)成为近几年来迅速发展的新型太阳能电池,其中将SnO₂纳米粒子层用作电子传输层(ETL)的钙钛矿太阳能电池器件得到了广泛的关注。SnO₂有着更低的制备温度,使其具备应用于柔性器件的潜力,但与钙钛矿层能级不匹配等问题限制着其发展。而在界面处加入钝化层,尤其是表面卤化的方法或可解决这一问题。本文综合研究了SnO₂表面卤化对钙钛矿太阳能电池光伏性能的影响,选用四丁基氯化铵(TBAC)、四丁基溴化铵(TBAB)和四丁基碘化铵(TBAI)三种钝化材料对SnO₂表面进行钝化处理,并对钝化材料溶液进行了浓度梯度研究。通过材料形貌、结构和光学性能表征以及电池器件性能测试分析等方法,证明了SnO₂表面卤化可提高钙钛矿层的质量和PSCs光伏性能,并从器件内部电荷传输动力学等角度解释了器件性能改善的原因。为进一步说明其性能改善的机理,采用基于密度泛函理论(DFT)的第一性原理计算方法对材料表面性质进行了深入研究,从能量、结构、电荷密度、态密度、功函数等角度解释了表面卤化提高SnO₂/钙钛矿界面处电子传输特性的原因。实验和理论计算均表明TBAC对于SnO₂具有较好的钝化效果,并随着溶液浓度的提升钝化作用越明显。SnO₂表面卤化作用的深入研究不仅对提高电池器件性能具有实际意义,还能够帮助理解太阳能电池界面现象,为界面改性提供新的研究思路。     

High-Efficiency Perovskite Solar Cells Enabled by Anatase TiO2 Nanopyramid Arrays with an Oriented Electric Field

One-dimensional (1D) nanostructured oxides are proposed as excellent electron transport materials (ETMs) for perovskite solar cells (PSCs); however, experimental evidence is lacking. A facile hydrothermal approach was employed to grow highly oriented anatase TiO₂ nanopyramid arrays and demonstrate their application in PSCs. The oriented TiO₂ nanopyramid arrays afford sufficient contact area for electron extraction and increase light transmission. Moreover, the nanopyramid array/perovskite system exhibits an oriented electric field that can increase charge separation and accelerate charge transport, thereby suppressing charge recombination. The anatase TiO₂ nanopyramid array-based PSCs deliver a champion power conversion efficiency of approximately 22.5 %, which is the highest power conversion efficiency reported to date for PSCs consisting of 1D ETMs. This work demonstrates that the rational design of 1D ETMs can achieve PSCs that perform as well as typical mesoscopic and planar PSCs.     

In Situ Photocatalytically Heterostructured ZnOAg Nanoparticle Composites as Effective Cathode‐Modifying Layers for Air‐Processed Polymer Solar Cells

A heterostructured semiconductor–metal ZnO?Ag nanoparticle (NP) composite was constructed through a straightforward photocatalytic strategy by using UV irradiation of ZnO NPs and an aqueous solution of Ag precursor. The ZnO?Ag NP composites serve as an effective cathode‐modifying layer in polymer solar cells (PSCs) with increased short‐circuit current density owing to the light‐trapping effect, and improved optical and electrical conductivity properties compared with pure ZnO NPs. The Ag NPs, which are photodeposited in situ on ZnO NPs, can act as effective antennas for incident light to maximize light harvesting and minimize radiative decay or nonradiative losses, consequently resulting in the enhanced photogeneration of excitons in PSCs. Systematic photoelectron and ‐physical investigations confirm that heterostructured ZnO?Ag NPs can significantly improve charge separation, transport, and collection, as well as lower charge recombination at the cathode interface, leading to a 14.0 % improvement in air‐processed device power conversion efficiency. In addition, this processable, cost‐effective, and scalable approach is compatible with roll‐to‐roll manufacturing of large‐scale PSCs.     

Alkyl-Chain-Regulated Charge Transfer in Fluorescent Inorganic CsPbBr3 Perovskite Solar Cells

Improved charge extraction and wide spectral absorption promote power conversion efficiency of perovskite solar cells (PSCs). The state-of-the-art carbon-based CsPbBr₃ PSCs have an inferior power output capacity because of the large optical band gap of the perovskite film and the high energy barrier at perovskite/carbon interface. Herein, we use alkyl-chain regulated quantum dots as hole-conductors to reduce charge recombination. By precisely controlling alkyl-chain length of ligands, a balance between the surface dipole induced charge coulomb repulsive force and quantum tunneling distance is achieved to maximize charge extraction. A fluorescent carbon electrode is used as a cathode to harvest the unabsorbed incident light and to emit fluorescent light at 516 nm for re-absorption by the perovskite film. The optimized PSC free of encapsulation achieves a maximum power conversion efficiency up to 10.85 % with nearly unchanged photovoltaic performances under 80 %RH, 80 °C, or light irradiation in air.     

A universal tactic of using Lewis-base polymer-CNTs composites as additives for high performance cm~2-sized and flexible perovskite solar cells

Lewis-base polymers have been widely utilized as additives to act as a template for the perovskite nucleation/crystal growth and passivate the under-coordinated Pb2+ sites.However,it is uncovered in this work that the polymer on the perovskite grain boundaries would significantly hinder the charge transport due to its low conductivity,which brings about free carrier recombination and photocurrent losses.To circumvent this issue while fully exploiting the benefits of polymers in passivating the trap states in perovskite,we incorporate highly conductive multiwall carbon nanotubes(CNTs) with Lewis-base polymers as coadditives in the perovskite film.Functionalizing the CNTs with-COOH group enables a selective hole-extraction and charge transport from perovskite to the hole transporting materials(HTM).By studying the charge transporting and recombination dynamics,we revealed the individual role of the polymer and CNTs in passivating the trap states and facilitating the charge transport,respectively.As a result,the perovskite solar cells(PSCs) with polymer-CNTs composites exhibit an impressive PCE of 21.7% for a small-area device(0.16 cm2) and 20.7% for a large-area device(1.0 cm2).Moreover,due to the superior mechanical flexibility of both polymer and CNTs,the polymer-CNTs composites incorporation in the perovskite film encourages the fabrication of flexible PSCs(f-PSCs) with an impressive PCE of 18.3%,and a strong mechanical durability by retaining 80%of the initial PCE after 1,000 times bending.In addition,we proved that the selection criteria of the polymers can be extended to other long-chain Lewis-base polymers,which opens new possibilities in design and synthesis of inexpensive material for this tactic towards the fabrication of high performance large-area PSCs and f-PSCs.     

High‐Efficiency Perovskite Solar Cells Enabled by Anatase TiO2 Nanopyramid Arrays with an Oriented Electric Field

One‐dimensional (1D) nanostructured oxides are proposed as excellent electron transport materials (ETMs) for perovskite solar cells (PSCs); however, experimental evidence is lacking. A facile hydrothermal approach was employed to grow highly oriented anatase TiO₂ nanopyramid arrays and demonstrate their application in PSCs. The oriented TiO₂ nanopyramid arrays afford sufficient contact area for electron extraction and increase light transmission. Moreover, the nanopyramid array/perovskite system exhibits an oriented electric field that can increase charge separation and accelerate charge transport, thereby suppressing charge recombination. The anatase TiO₂ nanopyramid array‐based PSCs deliver a champion power conversion efficiency of approximately 22.5 %, which is the highest power conversion efficiency reported to date for PSCs consisting of 1D ETMs. This work demonstrates that the rational design of 1D ETMs can achieve PSCs that perform as well as typical mesoscopic and planar PSCs.     

Eliminating Hysteresis of Perovskite Solar Cells with Hollow TiO2 Mesoporous Electron Transport Layer

Current density-voltage(J-V) hysteresis issue caused by unbalanced charge transport has greatly limited the improvement of power conversion efficiency(PCE) of halide perovskite solar cells(PSCs). Herein, hollow TiO₂ mesoporous electron transport layer(ETL) was used to fabricate PSCs. The structure-dependent charge collection as well as its effect on PCE and hysteresis impactor(HI) of PSC were investigated. The results demonstrate that TiO₂ hollow spheres in a size of around 50 nm (HS-50) can form a high quality perovskite/ETL interface with a less trap density. Moreover, the hollow TiO₂ with the thin shell can help promote the extraction of electrons from perovskite layer to ETL, so as to reduce the charge accumulation and recombination at the perovskite/ETL interface and alleviate the hysteresis behavior. As a result, PSCs with HS-50 TiO₂ delivered a champion PCE of 16.81% with a small HI of 0.0297, indicating a better performance than the commercial P25(PCE of 15.87%, HI of 0.2571).     

ZnS nanoparticle decorated ZnO nanowall network: investigation through electron microscopy and secondary ion mass spectrometry

We report on the fabrication of ZnO nanowall networks decorated with ZnS nanostructures on aluminum substrates using simple chemical route. The structural features and elemental constituents of the ZnS/ZnO heterostructure systems have been extensively studied using electron microscopy and energy dispersive X‐ray spectroscopy. The light emission characteristics of the bare and heterostructured systems have been analyzed using room temperature photoluminescence spectroscopy. The decoration of ZnS nanostructures over ZnO nanowalls has been evidenced through secondary ion mass spectrometry (SIMS). The ‘matrix effect’ has been found to be prominent during SIMS analysis of the bare and heterostructured nanowalls indicating the presence of ZnS phase over ZnO surface. ‘MCs⁺‐SIMS’ has been employed to suppress the matrix effect and is found to be potentially effective in making a semi‐quantitative estimation of Zn and O surface–atom concentrations in both systems. The luminescence responses of the ZnS/ZnO heterostructures have been found to be strongly dependent on the extent of ZnS phase over ZnO. The higher luminescence responses in ZnS/ZnO heterostructures fabricated with smaller ZnS nanoparticles have been explained in terms of a mechanism of charge‐carrier transfer from ZnS to ZnO. Copyright © 2014 John Wiley & Sons, Ltd.     

Alkyl‐Chain‐Regulated Charge Transfer in Fluorescent Inorganic CsPbBr3 Perovskite Solar Cells

Improved charge extraction and wide spectral absorption promote power conversion efficiency of perovskite solar cells (PSCs). The state‐of‐the‐art carbon‐based CsPbBr₃ PSCs have an inferior power output capacity because of the large optical band gap of the perovskite film and the high energy barrier at perovskite/carbon interface. Herein, we use alkyl‐chain regulated quantum dots as hole‐conductors to reduce charge recombination. By precisely controlling alkyl‐chain length of ligands, a balance between the surface dipole induced charge coulomb repulsive force and quantum tunneling distance is achieved to maximize charge extraction. A fluorescent carbon electrode is used as a cathode to harvest the unabsorbed incident light and to emit fluorescent light at 516 nm for re‐absorption by the perovskite film. The optimized PSC free of encapsulation achieves a maximum power conversion efficiency up to 10.85 % with nearly unchanged photovoltaic performances under 80 %RH, 80 °C, or light irradiation in air.     

A mini review: Constructing perovskite p-n homojunction solar cells

Organic metal halide perovskite materials have excellent photoelectric properties, and the power conversion efficiency(PCE) of the perovskite solar cells(PSCs) has increased from 3.8% to more than 25%. In the development of PSCs, innovative architectures were being proposed constantly. However, the use of the electron transport layer(ETL) and hole transport layer(HTL) increases manufacturing costs and process complexity. Perovskite material has ambipolar charge transport characteristics, so it c...     

Dual-Interface Engineering in Perovskite Solar Cells with 2D Carbides

Passivating the interfaces between the perovskite and charge transport layers is crucial for enhancing the power conversion efficiency (PCE) and stability in perovskite solar cells (PSCs). Here we report a dual-interface engineering approach to improving the performance of FA_0.85MA_0.15Pb(I_0.95Br_0.05)₃-based PSCs by incorporating Ti₃C₂Cl_x Nano-MXene and o-TB-GDY nanographdiyne (NanoGDY) into the electron transport layer (ETL)/perovskite and perovskite/ hole transport layer (HTL) interfaces, respectively. The dual-interface passivation simultaneously suppresses non-radiative recombination and promotes carrier extraction by forming the Pb−Cl chemical bond and strong coordination of π-electron conjugation with undercoordinated Pb defects. The resulting perovskite film has an ultralong carrier lifetime exceeding 10 μs and an enlarged crystal size exceeding 2.5 μm. A maximum PCE of 24.86 % is realized, with an open-circuit voltage of 1.20 V. Unencapsulated cells retain 92 % of their initial efficiency after 1464 hours in ambient air and 80 % after 1002 hours of thermal stability test at 85 °C.     

Fully Aromatic Self-Assembled Hole-Selective Layer toward Efficient Inverted Wide-Bandgap Perovskite Solar Cells with Ultraviolet Resistance

Ultraviolet-induced degradation has emerged as a critical stability concern impeding the widespread adoption of perovskite solar cells (PSCs), particularly in the context of phase-unstable wide-band gap perovskite films. This study introduces a novel approach by employing a fully aromatic carbazole-based self-assembled monolayer, denoted as (4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)phosphonic acid (MeO-PhPACz), as a hole-selective layer (HSL) in inverted wide-band gap PSCs. Incorporating a conjugated linker plays a pivotal role in promoting the formation of a dense and highly ordered HSL on substrates, facilitating subsequent perovskite interfacial interactions, and fostering the growth of uniform perovskite films. The high-quality film could effectively suppress interfacial non-radiative recombination, improving hole extraction/transport efficiency. Through these advancements, the optimized wide-band gap PSCs, featuring a band gap of 1.68 eV, attain an impressive power conversion efficiency (PCE) of 21.10 %. Remarkably, MeO-PhPACz demonstrates inherent UV resistance and heightened UV absorption capabilities, substantially improving UV resistance for the targeted PSCs. This characteristic holds significance for the feasibility of large-scale outdoor applications.     

Perovskite solar cells: Thermal and chemical stability improvement,and economic analysis

Perovskite solar cells (PSCs) are highly efficient and are comparatively cheaper than the large silicon crystals primarily used in solar cells. Their outstanding photovoltaic performance makes them a potential alternative to silicon solar cells. While efficiency and photovoltaic performance have been investigated in recent decades, a knowledge gap on the degradation, economic feasibility and stability of PSCs exists, and their poor stability remains a barrier to commercialization. Thus, this review aims to fill this knowledge gap by focusing on approaches to improve PSCs’ thermal and chemical stability, and their economic viability under different conditions. The structure and manufacture of PSCs are also discussed along with an economic analysis of different perovskite devices. Improvements in thermal stability can be reached by incorporating inorganic materials into the PSC. A PSC model optimized with ZnO improves chemical stability by 8% and works well under low temperatures. To make PSCs more economically feasible, certain parts like counter electrodes (CE) and hole transport materials (HTMs) can be replaced with alternative elements like carbon and inorganic HTMs, respectively. PSCs with long durability and high conversion efficiency will expand the commercial prospects for this material. To bridge the lack of knowledge, further investigation is required on the sustainability and longevity of PSCs.     

CuO Quantum‐Dot‐Sensitized Mesoporous ZnO for Visible‐Light Photocatalysis

How to extend ultraviolet photocatalysts to the visible‐light region is a key challenge for solar‐driven photocatalysis. Herein, we show that ultraviolet ZnO photocatalysts can present high visible‐light photocatalytic activity when combined with CuO quantum dots (QDs; <3 nm). Theoretical analysis demonstrates that the quantum size effect plays a key role in the photoactivity of the CuO/ZnO composite. For CuO QDs smaller than 3 nm, the separated charges could transfer from CuO QDs to the conduction bands of ZnO due to quantum splitting of the CuO energy level and phonon compensation for the difference in the conduction band minimum of CuO and ZnO; however, this process would not occur with the disappearance of the quantum size effect. Further structural analysis demonstrates that interfacial charge separation and transfer between ZnO and CuO dominate the photocatalytic processes instead of a single CuO or ZnO surface. Compared with ZnO? noble metal structures (e.g., ZnO? Ag or ZnO? Au), these ZnO? CuO QD composites present wider absorption bands, higher visible photocatalytic efficiencies, and lower costs.     

核壳结构CdS/ZnS纳米微粒的制备与光学特性

CdS and CdS/ZnS core-shell structure nano particles were synthesized in micro emulsion, and characterized by X-ray diffraction(XRD), transmission electron microscopy (TEM), UV absorption spectra and PL. The average diameter of CdS was about 3.3 nm, and CdS/ZnS core-shell structure was confirmed by XRD and UV. Considering the optical properties of CdS/ZnS core-shell structure nanoparticles which have different ZnS shell thickness, the UV absorption edge of CdS/ZnS becomes as lightred-shift with the thickness of ZnS layer increasing, and the absorption of shortwave band is strongly enhanced at the same time. The PL spectra indicate that ZnS shell layer can greatly eliminate surface defects of CdS nanoparticles and make its band-edge directed recombination increased, and the luminous efficiency of CdS is improved greatly when it has appropriate shell thickness.