Nanotetrapods: quantum dot hybrid for bulk heterojunction solar cells

Hybrid thin film solar cell based on all-inorganic nanoparticles is a new member in the family of photovoltaic devices. In this work, a novel and performance-efficient inorganic hybrid nanostructure with continuous charge transportation and collection channels is demonstrated by introducing CdTe nanotetropods (NTs) and CdSe quantum dots (QDs). Hybrid morphology is characterized, demonstrating an interpenetration and compacted contact of NTs and QDs. Electrical measurements show enhanced charge transfer at the hybrid bulk heterojunction interface of NTs and QDs after ligand exchange which accordingly improves the performance of solar cells. Photovoltaic and light response tests exhibit a combined optic-electric contribution from both CdTe NTs and CdSe QDs through a formation of interpercolation in morphology as well as a type II energy level distribution. The NT and QD hybrid bulk heterojunction is applicable and promising in other highly efficient photovoltaic materials such as PbS QDs.     

Solution-processed, nanostructured hybrid solar cells with broad spectral sensitivity and stability

Hybrid organic-inorganic solar cells, as an alternative to all-organic solar cells, have received significant attention for their potential advantages in combining the solution-processability and versatility of organic materials with high charge mobility and environmental stability of inorganic semiconductors. Here we report efficient and air-stable hybrid organic-inorganic solar cells with broad spectral sensitivity based on a low-gap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and spherical CdSe nanoparticles. The solvents used for depositing the hybrid PCPDTBT:CdSe active layer were shown to strongly influence the film morphology, and subsequently the photovoltaic performance of the resulted solar cells. Appropriate post-deposition annealing of the hybrid film was also shown to improve the solar cell efficiency. The inclusion of a thin ZnO nanoparticle layer between the active layer and the metal cathode leads to a significant increase in device efficiency especially at long wavelengths, due to a combination of optical and electronic effects including more optimal light absorption in the active layer and elimination of unwanted hole leakage into the cathode. Overall, maximum power conversion efficiencies up to 3.7 ± 0.2% and spectral sensitivity extending above 800 nm were achieved in such PCPDTBT:CdSe nanosphere hybrid solar cells. Furthermore, the devices with a ZnO nanoparticle layer retained ～70% of the original efficiency after storage under ambient laboratory conditions for over 60 days without any encapsulation.     

CdSe nanocrystal sensitized ZnO core-shell nanorod array films: Preparation and photovoltaic properties

ZnO/CdSe core-shell nanorod array films were synthesized via a two-step method. ZnO nanorod array films were first grown on a TCO substrate, and then CdSe nanocrystals were deposited on the nanorods to form core-shell structured films. The resulting films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis absorption spectroscopy. Especially, dark-field images and transmission electron diffraction of the TEM were used to study the morphology and the chemical nanostructure of the ZnO/CdSe core-shell nanorods in detail. We investigated the photovoltaic performance of the resulting ZnO/CdSe core-shell nanorod array films as solar cell photoanodes. Parameters, such as the length of the ZnO nanorods, the shell phase structure and the deposition time of the CdSe nanocrystals were found to affect the photovoltaic performance of the solar cell. This study provides a facile method to prepare nanocomposite photoanodes of solar cells, and gives some insight about the fundamental mechanisms that improve the performance.     

Solid‐state dye‐sensitized and bulk heterojunction solar cells using TiO2 and ZnO nanostructures: recent progress and new concepts at the borderline

In the field of photovoltaic energy conversion, hybrid inorganic/organic devices represent promising alternatives to standard photovoltaic systems in terms of exploiting the specific features of both organic semiconductors and inorganic nanomaterials. Two main categories of hybrid solar cells coexist today, both of which make much use of metal oxide nanostructures based on titanium dioxide (TiO₂) and zinc oxide (ZnO) as electron transporters. These metal oxides are cheap to synthesise, are non‐toxic, are biocompatible and have suitable charge transport properties, all these features being necessary to demonstrate highly efficient solar cells at low cost. Historically, the first hybrid approach developed was the dye‐sensitized solar cell (DSSC) concept based on a nanostructured porous metal oxide electrode sensitized by a molecular dye. In particular, solid‐state hybrid DSSCs, which reduce the complexity of cell assembly, demonstrate very promising performance today. The second hybrid approach exploits the bulk heterojunction (BHJ) concept, where conjugated polymer/metal oxide interfaces are used to generate photocurrent. In this context, we review the recent progress and new concepts in the field of hybrid solid‐state DSSC and BHJ solar cells based on TiO₂ and ZnO nanostructures, incorporating dyes and conjugated polymers. We point out the specificities in common hybrid device structures and give an overview on new concepts, which couple and exploit the main advantages of both DSSC and BHJ approaches. In particular, we show that there is a trend of convergence between both DSSC and BHJ approaches into mixed concepts at the borderline which may allow in the near future the development of hybrid devices for competitive photovoltaic energy conversion. Copyright © 2011 Society of Chemical Industry     

In situ synthesis of P3HT-capped CdSe superstructures and their application in solar cells

Organic/inorganic hybrid solar cells have great potentials to revolutionize solar cells, but their use has been limited by inefficient electron/hole transfer due to the presence of long aliphatic ligands and unsatisfying continuous interpenetrating networks. To solve this problem, herein, we have developed a one-pot route for in situ synthesis of poly(3-hexylthiophene) (P3HT)-capped CdSe superstructures, in which P3HT acts directly as the ligands. These CdSe superstructures are in fact constructed from numerous CdSe nanoparticles. The presence of P3HT ligands has no obvious adverse effects on the morphologies and phases of CdSe superstructures. Importantly, higher content of P3HT ligands results in stronger photoabsorption and fluorescent intensity of CdSe superstructure samples. Subsequently, P3HT-capped CdSe superstructures prepared with 50 mg P3HT were used as a model material to fabricate the solar cell with a structure of PEDOT:PSS/P3HT-capped CdSe superstructures: P3HT/Al. This cell gives a power conversion efficiency of 1.32%.     

Effect of CdSe quantum dots on the performance of hybrid solar cells based on ZnO nanorod arrays

This paper reports the fabrication and interface modification of hybrid inverted solar cells based on ZnO nanorod arrays and poly (3-hexylthiophene). CdSe quantum dots (QDs) are grafted to the ZnO nanorod array successfully by bifunctional molecule mercaptopropionic acid to enhance the device performance. The power conversion efficiency of the device is increased by 109% from 0.11% to 0.23% under simulated 1 sun AM 1.5 solar illumination at 100 mW/cm² after the modification. The grafting of CdSe QDs effectively enhanced the excition generation and dissociation on the organic/inorganic interface. This work may provide a general method for increasing the efficiency of organic–inorganic hybrid solar cells by interface modification.     

Recent Progress on Reduced Graphene Oxide-Based Counter Electrodes for Cost-Effective Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are one type of highly efficient low-cost solar cells among third-generation photovoltaic devices. Replacing the expensive components of DSSCs with alternative inexpensive and earth-abundant materials would further reduce their price in the solar cell market. Recently, graphene-based low-cost counter electrodes (CEs) have been developed, which could serve as a potential alternative to the expensive platinum-based CEs. In this review article, we have summarized recent research on various reduced graphene oxide (rGO)-based composite CE materials, methods for their synthesis, their catalytic activity, and the effective utilization of such CEs in DSSCs. The photovoltaic performance of DSSCs made of rGO-based composite CEs were compared with the reference Pt-based cells, and the photovoltaic parameters are summarized in tables.     

Anisotropic core–shell nanocomposites by direct covalent attachment of a side-functionalized poly(3-hexylthiophene) onto ZnO nanowires

Inorganic-organic hybrid solar cells have demonstrated great potential for the development of next generation flexible electronics to deliver efficient energy conversion. The interfacial morphology and structure between donor and acceptor are determinative to the device performance. Here, we report on novel core–shell hybrid heterojunction nanostructures by covalently grafting side-functionalized poly(3-hexylthiophene) onto ZnO nanowires without ligand linkers. Solvatochromism of polythiophene is utilized to control the polymer morphology at interface. Study into the photophysics of nanohybrids demonstrates an elongated conjugation length of the polymer backbone at the interface and fast interfacial charge transfer. These results provide critical insight into the utilization of molecular composites to control donor–acceptor interfaces and further enable the use of anisotropic nanohybrids as photovoltaic elements for the massive fabrication of high efficiency devices.     

Influence of seed layer treatment on low temperature grown ZnO nanotubes: Performances in dye sensitized solar cells

Non-aligned and highly densely aligned ZnO nanotube (NTs), synthesized by low temperature solution method were applied as photoanode materials for the fabrication of efficient dye-sensitized solar cells (DSSCs). The crystalline and the morphological analysis revealed that the grown aligned ZnO NTs possessed a typical hexagonal crystal structure of outer and inner diameter ∼250 nm and ∼100 nm, respectively. ZnO seeding on FTO substrates is an essential step to achieve the aligned ZnO NTs. A DSSC fabricated with aligned ZnO NTs photoanode achieved high solar-to-electricity conversion efficiency of ∼2.2% with short circuit current (J_SC) of 5.5 mA/cm², open circuit voltage (V_OC) of 0.65 V and fill factor (FF) of 0.61. Significantly, the aligned ZnO NTs photoanode showed three times improved solar-to-electricity conversion efficiency than DSSC fabricated with non-aligned ZnO NTs. The enhanced performances were credited to the aligned morphology of ZnO NTs which executed the high charge collection and the transfer of electrons at the interfaces of ZnO NTs and electrolyte layer.     

Inorganic Quantum Dot Materials and their Applications in “Organic” Hybrid Solar Cells

Semiconductor quantum dots (QDs) are promising materials for polymer‐nanocrystal hybrid solar cells (HSCs). The aim of this review article is to present a comprehensive and current overview of inorganic QDs and their applications in HSCs. Fundamental properties of QDs are first illustrated. And then recent studies that have been done to elucidate charge dynamics of QDs and improve hybrid device performance are summarised and discussed in detail. Finally, an outlook is presented considering current existing challenges in HSCs.     

钙钛矿太阳电池的研究进展

介绍了卤铅铵钙钛矿（CH3NH3PbX3,X = Cl、Br、I）的结构及其在新型无机-有机杂化异质结钙钛矿太阳电池中的应用,阐述了钙钛矿太阳电池的结构与工作原理,着重从钙钛矿太阳电池的致密层、钙钛矿吸收层（有骨架层和无骨架层）及有机空穴传输层三个重要组成部分的材料、微结构及制备方法等方面分析了钙钛矿太阳电池的研究进展及存在的问题。并结合不同课题组的研究成果评价了钙钛矿太阳电池各组成部分相应的材料、微结构及制备方法等对太阳电池光伏性能和长期稳定性的影响。此外还介绍并比较了反转结构与柔性太阳电池的光伏性能,简要讨论了钙钛矿太阳电池的各层材料、结构、有毒重金属的替代、长期稳定性等方面的发展趋势。     

Controlling the morphology of trioctyl phosphine oxide-coated cadmium selenide/poly 3-hexyl thiophene composite active layer for bulk hetero-junction solar cells

Bulk hetero-junction solar cells with CdSe nanoparticles-P₃HT (poly 3-hexyl thiophene) composite active layer were fabricated, and the control of morphological feature of the nanoparticle-polymer composite thin films was investigated. A binary solvent composed of a primary solvent with intermediate polarity and a secondary solvent with high polarity was found to be effective in controlling the dispersion of the CdSe nanocrystals in the P₃HT matrix, and the modification of the nanocrystal surface by liquid-liquid extraction process was found to be effective in achieving the desired composite film morphology. Surface roughness of the active layer was optimized for various loadings of CdSe nanoparticles and could be reproducibly controlled to less than 10 nm.     

N-Ion-implanted TiO2 photoanodes in quantum dot-sensitized solar cells

Hierarchical nanostructured titanium dioxide (TiO(2)) clumps were fabricated using electrostatic spray with subsequent nitrogen-ion doping by an ion-implantation technique for improvement of energy conversion efficiency for quantum dot-sensitized solar cells (QDSCs). CdSe quantum dots were directly assembled on the produced N-ion-implanted TiO(2) photoanodes by chemical bath deposition, and their photovoltaic performance was evaluated in a polysulfide electrolyte with a Pt counter electrode. We found that the photovoltaic performance of TiO(2) electrodes was improved by nearly 145% upon N-ion implantation. The efficiency improvement seems to be due to (1) the enhancement of electron transport through the TiO(2) layer by inter-particle necking of primary TiO(2) particles and (2) an increase in the recombination resistance at TiO(2)/QD/electrolyte interfaces by healing the surface states or managing the oxygen vacancies upon N-ion doping. Therefore, N-ion-doped photoanodes offer a viable pathway to develop more efficient QD or dye-sensitized solar cells.     

Improvement of the physical properties of ZnO/CdTe core-shell nanowire arrays by CdCl2 heat treatment for solar cells

CdTe is an important compound semiconductor for solar cells, and its use in nanowire-based heterostructures may become a critical requirement, owing to the potential scarcity of tellurium. The effects of the CdCl₂ heat treatment are investigated on the physical properties of vertically aligned ZnO/CdTe core-shell nanowire arrays grown by combining chemical bath deposition with close space sublimation. It is found that recrystallization phenomena are induced by the CdCl₂ heat treatment in the CdTe shell composed of nanograins: its crystallinity is improved while grain growth and texture randomization occur. The presence of a tellurium crystalline phase that may decorate grain boundaries is also revealed. The CdCl₂ heat treatment further favors the chlorine doping of the CdTe shell with the formation of chlorine A-centers and can result in the passivation of grain boundaries. The absorption properties of ZnO/CdTe core-shell nanowire arrays are highly efficient, and more than 80% of the incident light can be absorbed in the spectral range of the solar irradiance. The resulting photovoltaic properties of solar cells made from ZnO/CdTe core-shell nanowire arrays covered with CuSCN/Au back-side contact are also improved after the CdCl₂ heat treatment. However, recombination and trap phenomena are expected to operate, and the collection of the holes that are mainly photo-generated in the CdTe shell from the CuSCN/Au back-side contact is presumably identified as the main critical point in these solar cells.     

Open-ended TiO2 nanotubes formed by two-step anodization and their application in dye-sensitized solar cells

We demonstrate a simple method to fabricate open-ended TiO(2) nanotube (NT) based dye-sensitized solar cells (DSSCs), where the NTs are attached to either TiO(2) nanorods (NRs) grown on fluorine-doped tin oxide (FTO) or FTO directly by nanoparticles (NPs). A completely hole-through TiO(2) NT layer is fabricated via a two-step anodization with heat treatment immediately after the first anodization. DSSCs with the open-ended NTs show better photovoltaic performance than those with close-ended NTs, due to the enhanced charge transport in the open-ended structure. Under optimum conditions, DSSCs fabricated with the open-ended NT layer exhibit a short circuit current density (J(sc)) of 19.10 mA cm(-2), an open circuit voltage (V(oc)) of 0.68 V, a fill factor (FF) of 0.49, and a power conversion efficiency (eff) of 6.3%.     

Semiconductor nanostructure-based photovoltaic solar cells

Substantial efforts have been devoted to design, synthesize, and integrate various semiconductor nanostructures for photovoltaic (PV) solar cells. In this article, we will review the recent progress in this exciting area and cover the material chemistry and physics related to all-inorganic nanostructure solar cells, hybrid inorganic nanostructure-conductive polymer composite solar cells, and dye-sensitized solar cells.     

Sb2S3太阳能电池的研究进展

Sb₂S₃太阳能电池相比于其他太阳能电池如铜铟镓硒、碲化镉和有机-无机钙钛矿等,具有成本低、无毒性、稳定性高的优点,并且Sb₂S₃材料本身拥有优良的光学性能,如带隙宽度为1.5～2.2eV、光吸收系数高达105cm–1,因此在太阳能转化方面具有良好的应用前景。但目前Sb₂S₃太阳能电池的光电转化效率仍然不高,其最高光电转化效率仅有7.5%,远低于发展成熟的单晶硅太阳能电池、铜铟镓硒、碲化镉太阳能电池。本文简要介绍了Sb₂S₃太阳能电池的工作原理,从光阳极、吸光层Sb₂S₃、空穴传输层3个方面阐述了其发展现状及存在的问题。随后针对限制光电转化效率的因素,阐述了现有的优化电池性能的方法及其研究进展。最后对Sb₂S₃太阳能电池的未来发展方向进行了展望,基于对现有研究分析认为,在未来的研究中需要进一步探索新型的光阳极半导体的种类和结构,研究简单低耗、结晶性良好的Sb₂S₃薄膜的制备方法,研究具有高电子传导率、与Sb₂S₃和对电极接触良好的空穴传输层以及发展高效界面修饰以及金属离子掺杂的方法,以提高Sb₂S₃太阳能电池的性能。     

The hybrid halide perovskite: Synthesis strategies,fabrications, and modern applications

The organic–inorganic hybrid halide perovskite has several outstanding properties that are beneficial for optoelectronic and photovoltaic applications. Their interesting properties and the use in several modern application, attracted attention of the materials researchers. However, in this review, we describe how hybrid perovskite-based solar cells has become an important renewable source of energy along with historical background and the future of this potential material. We also describe the synthesis and fabrication methods for preparing ultrathin to bulk perovskites and their crystallographic nature of pure and mixed metallic hybrid perovskite system. This review not only focused on properties of hybrid perovskite but also represents the drawback as well as the development and performance in different fields of application.     

A Novel Method for Preparing Vertically Aligned CdS Nanorod Arrays and Its Application in Photovoltaic Cells with P3HT Fibers

Vertically aligned cadmium sulfide (CdS) nanorod arrays were prepared through a novel thermal annealing route. By embedding the as-prepared CdS nanorod arrays into the poly(3-hexylthiophene) (P3HT) nanofiber (NF) matrix, the photovoltaic devices were fabricated with the structure of ITO/PEDOT:PSS/CdS arrays/P3HT NF/Au. The device performance was highly dependent on the P3HT NF layer thickness in this structure, and a power conversion efficiency (PCE) of 0.23 % was obtained for optimal P3HT NF layer thickness of 150 nm. In addition, much higher PCE of 0.84 % was achieved after post-annealing. The significantly improved photovoltaic performance may be caused by the increased interfacial areas between P3HT NFs and CdS nanorods for efficient charge separation, as well as the decreased inter-nanocrystal distance caused by insulating organic ligands after the annealing treatment. The results demonstrate a promising inorganic–organic hybrid photovoltaic structure with vertically aligned CdS nanorods arrays.     

A simple and scalable graphene patterning method and its application in CdSe nanobelt/graphene Schottky junction solar cells

We have developed a simple and scalable graphene patterning method using electron-beam or ultraviolet lithography followed by a lift-off process. This method, with the merits of: high pattern resolution and high alignment accuracy, being free from additional etching or harsh processes, being universal to arbitrary substrates, and being compatible to Si microelectronic technology, can easily be applied to diverse graphene-based devices, especially in array-based applications, where large-scale graphene patterns are desired. We have applied this method to fabricate CdSe nanobelt (NB)/graphene Schottky junction solar cells, which have potential applications in integrated nano-optoelectronic systems. A typical as-fabricated solar cell shows excellent photovoltaic behavior, with an open-circuit voltage of ～0.51 V, a short-circuit current density of ～5.75 mA cm(-2), and an energy conversion efficiency of ～1.25%. We attribute the high performance of the cell to the as-patterned high-performance graphene, which can form an ideal Schottky contact with CdSe NB. Our results suggest that both the developed graphene patterning method and the as-fabricated CdSe NB/graphene Schottky junction solar cells have reachable application prospects.