Boosting the Performance of Environmentally Friendly Quantum Dot‐Sensitized Solar Cells over 13% Efficiency by Dual Sensitizers with Cascade Energy Structure

Generally, high light‐harvesting efficiency, electron‐injection efficiency, and charge‐collection efficiency are the prerequisites for high‐efficiency quantum‐dot‐sensitized solar cells (QDSCs). However, it is fairly difficult for a single QD sensitizer to meet these three requirements simultaneously. It is demonstrated that these parameters can be felicitously balanced by a cosensitization strategy through the adoption of environmental‐friendly Zn–Cu–In–Se and Zn–Cu–In–S dual QD sensitizers with cascade energy structure. Experimental results indicate that: i) the combination of the dual QDs can improve the light‐harvesting capability of the cells, especially in the visible light window; ii) the cosensitization approach can facilitate electron injection, benefitting from the cascade energy structure of the two QD sensitizers employed; iii) the charge‐collection efficiency can be remarkably enhanced by the suppressed charge‐recombination process due to the improved QD coverage on TiO₂. Consequently, this cosensitization strategy delivers a new certified efficiency record of 12.98% for liquid‐junction QDSCs under AM 1.5G 1 sun irradiation. Moreover, the constructed cells exhibit good stability in a high‐humidity environment.     

Preparation and characterization of TiO2 anode film with spinodal phase separation structure in dye-sensitized solar cells

Low electronic transmission efficiency and high charge recombination are the existing problems of photoanode film in traditional dye sensitized solar cells (DSSCs). This paper put forward the photoanode TiO₂ films with spinodal phase separation structure (SPSS) and continuous TiO₂ skeleton which were triggered by the photopolymerization of organic monomers in a photomonomer-inorganic precursor system. The photoanode TiO₂ films fabricated by different precursor solution compositions and different coating layers were characterized mainly by scanning electron microscopy (SEM), photocatalysis and photoelectric performance test. The results indicated that, the as-prepared TiO₂ anode film with seven coating layers and heat treated at 500 °C showed higher photoelectric conversion efficiency at about 2% than that of other samples with less coating layers and lower heat treatment temperature. The film also showed excellent photocatalytic activity by using methylene blue (MB) dye as a model organic substrate under fluorescent lamp irradiation. It is suggested that the film with SPSS structure has the potential to improve the electronic transmission efficiency and reduce the carrier recombination due to its particular structure, higher surface area, and lack of bottleneck in electronic transmission. It is worth noting that the SPSS structure provides new ideas to develop new photoanode films and further improve the photoelectric conversion performance of the DSSC in future.     

一维二氧化钛光阳极的制备及在染料敏化太阳能电池中的应用综述

二氧化钛由于具有合适的禁带宽度、良好的光电性能、制作工艺简单等特点,目前广泛应用于染料敏化太阳能电池中。其中,大部分光阳极主要是由纳米颗粒组成,但纳米颗粒不利于电子和空穴的分离及传输、染料敏化太阳能电池的光电转化效率的提升。因此,可采用一维纳米结构光阳极替换纳米颗粒,这有利于提升染料敏化太阳能电池的光电转化效率。一维纳米材料具有较少的晶界,可为电荷提供通道、加速电子的传输,且能有效减少空穴/电子的复合,减少电子与染料的复合,从而提高效率。同时一维二氧化钛其较大的比表面积,不仅有利于染料吸附量增加,而且能有效提高电流密度。综述了几种一维二氧化钛制备方法的最新研究进展,分析了不同制备方法对二氧化钛光阳极的能带结构、光吸收特性、染料吸附量和电子传输过程的影响,介绍了近几年一维二氧化钛在染料敏化太阳能中的应用。最后,对一维二氧化钛在染料敏化太阳能电池中的应用进行了展望。     

量子点敏化太阳能电池光阳极的研究进展

介绍量子点敏化太阳能电池的发展现状及趋势,针对光阳极改性来提高量子点敏化太阳能电池转化效率的方法,从半导体薄膜、量子点共敏化、量子点掺杂3个方面综合分析光阳极的研究进展和相关技术。根据制约电池效率的主要因素,提出量子点敏化太阳能电池的未来发展趋势,包括继续优化光阳极半导体薄膜的组成及结构、探索新型的宽光谱响应量子点以及发展高效的界面修饰技术等。     

Efficient and Stable Solid‐State Dye‐Sensitized Solar Cells Based on a High‐Molar‐Extinction‐Coefficient Sensitizer

The high‐molar‐extinction‐coefficient heteroleptic ruthenium dye, cis‐Ru (4,4′‐bis(5‐octylthieno[3,2‐b] thiophen‐2‐yl)‐2,2′‐bipyridine) (4,4′‐dicarboxyl‐2,2′‐bipyridine) (NCS)₂, exhibits an AM 1.5 solar (100 mW cm^?2)‐to‐electric power‐conversion efficiency of 4.6% in a solid‐state dye‐sensitized solar cell (SSDSC) with 2,2′, 7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)9,9′‐spirobifluorene (spiro‐MeOTAD) as the organic hole‐transporting material. These SSDSC devices exhibit good durability during accelerated tests under visible‐light soaking for 1000 h at 60 °C. This demonstration elucidates a class of photovoltaic devices with potential for stable and low‐cost power generation. The electron recombination dynamics and charge collection that take place at the dye‐sensitized heterojunction are studied by means of impedance and transient photovoltage decay techniques.     

One‐Step Fabrication of Unique Mesoporous NiO Hollow Sphere Film on FTO for High‐Performance P‐Type Dye‐Sensitized Solar Cells

P‐type dye sensitized solar cells (p‐DSCs) deliver much lower overall efficiency than their inverse model, n‐DSCs. However, they have fundamental and practical significance, in particular, their tandem structured solar cells with both p‐ and n‐photoelectrodes could offer great potential to significantly improve the efficiency of existing solar cells. A facile and environmentally friendly method is developed to directly one‐step grow hollow NiO spherical structures on fluorine‐doped tin oxide (FTO) substrate, in which a Ni²⁺ and polymer complex spherical structure is self‐constructed through a controlled solvent evaporation process, followed by calcination‐converting to a unique NiO hollow sphere film. The prepared material is further used as a photocathode in p‐type dye sensitized solar cells, resulting in 41% increase of an open‐circuit voltage and 18% enhancement of power conversion efficiency than NiO nanoparticles photocathode. The improved performance can be ascribed to suppressed charge recombination at the photocathode/electrolyte interface. This template‐free approach could be universally used to fabricate other nanostructured hollow spheres for a wide range of energy conversion applications such as electrochemical capacitors, chemical sensors, and electrochromic devices.     

Slow‐Photon‐Effect‐Induced Photoelectrical‐Conversion Efficiency Enhancement for Carbon‐Quantum‐Dot‐Sensitized Inorganic CsPbBr3 Inverse Opal Perovskite Solar Cells

All‐inorganic cesium lead halide perovskite is suggested as a promising candidate for perovskite solar cells due to its prominent thermal stability and comparable light absorption ability. Designing textured perovskite films rather than using planar‐architectural perovskites can indeed optimize the optical and photoelectrical conversion performance of perovskite photovoltaics. Herein, for the first time, this study demonstrates a rational strategy for fabricating carbon quantum dot (CQD‐) sensitized all‐inorganic CsPbBr₃ perovskite inverse opal (IO) films via a template‐assisted, spin‐coating method. CsPbBr₃ IO introduces slow‐photon effect from tunable photonic band gaps, displaying novel optical response property visible to naked eyes, while CQD inlaid among the IO frameworks not only broadens the light absorption range but also improves the charge transfer process. Applied in the perovskite solar cells, compared with planar CsPbBr₃, slow‐photon effect of CsPbBr₃ IO greatly enhances the light utilization, while CQD effectively facilitates the electron–hole extraction and injection process, prolongs the carrier lifetime, jointly contributing to a double‐boosted power conversion efficiency (PCE) of 8.29% and an increased incident photon‐to‐electron conversion efficiency of up to 76.9%. The present strategy on CsPbBr₃ IO to enhance perovskite PCE can be extended to rationally design other novel optoelectronic devices.     

Carbon Nanotubes for Dye‐Sensitized Solar Cells

As one type of emerging photovoltaic cell, dye‐sensitized solar cells (DSSCs) are an attractive potential source of renewable energy due to their eco–friendliness, ease of fabrication, and cost effectiveness. However, in DSSCs, the rarity and high cost of some electrode materials (transparent conducting oxide and platinum) and the inefficient performance caused by slow electron transport, poor light‐harvesting efficiency, and significant charge recombination are critical issues. Recent research has shown that carbon nanotubes (CNTs) are promising candidates to overcome these issues due to their unique electrical, optical, chemical, physical, as well as catalytic properties. This article provides a comprehensive review of the research that has focused on the application of CNTs and their hybrids in transparent conducting electrodes (TCEs), in semiconducting layers, and in counter electrodes of DSSCs. At the end of this review, some important research directions for the future use of CNTs in DSSCs are also provided.     

Novel Meso‐Superstructured Solar Cells with a High Efficiency Exceeding 12%

The dye‐sensitized solar cell (DSSC) is representative of next generation photovoltaic devices. State‐of‐the‐art DSSCs have been established for two decades. However, the recent application of organic‐inorganic hybrid perovskites on nanoparticle Al₂O₃ film has totally changed the DSSC structure, leading to a new type of solar cell — meso‐superstructured solar cells (MSSCs) with a high power conversion efficiency exceeding 12%. This article summarizes this impressive progress and discusses the challenges of MSSCs.     

Multidimensional Anodized Titanium Foam Photoelectrode for Efficient Utilization of Photons in Mesoscopic Solar Cells

Mesoscopic solar cells based on nanostructured oxide semiconductors are considered as a promising candidates to replace conventional photovoltaics employing costly materials. However, their overall performances are below the sufficient level required for practical usages. Herein, this study proposes an anodized Ti foam (ATF) with multidimensional and hierarchical architecture as a highly efficient photoelectrode for the generation of a large photocurrent. ATF photoelectrodes prepared by electrochemical anodization of freeze‐cast Ti foams have three favorable characteristics: (i) large surface area for enhanced light harvesting, (ii) 1D semiconductor structure for facilitated charge collection, and (iii) 3D highly conductive metallic current collector that enables exclusion of transparent conducting oxide substrate. Based on these advantages, when ATF is utilized in dye‐sensitized solar cells, short‐circuit photocurrent density up to 22.0 mA cm^?2 is achieved in the conventional N719 dye‐I₃^?/I^? redox electrolyte system even with an intrinsically inferior quasi‐solid electrolyte.     

Enhanced photovoltaic performance of quantum dot sensitized solar cells with Ag-doped TiO2 nanocrystalline thin films

Ag-doped titanium dioxide (TiO₂) nanocrystalline thin films have been prepared by the sol–gel dip coating method and used as photoanode to fabricate quantum dot sensitized solar cells. The X-ray diffraction studies reveal the formation of anatase phase without any impurity phase. The surface morphology studied using scanning electron microscope shows uniform distribution of particles. The optical band gap was found to be 3.5 and 3.4 eV for CdS quantum dot sensitized TiO₂ and CdS quantum dot sensitized Ag-doped TiO₂ thin film respectively. The Ag-doped TiO₂ based solar cell exhibited a power conversion efficiency of 1.48 % which is higher than that of TiO₂ (0.9 %).     

Ordered Single‐Crystalline Anatase TiO2 Nanorod Clusters Planted on Graphene for Fast Charge Transfer in Photoelectrochemical Solar Cells

Achieving efficient charge transport is a great challenge in nanostructured TiO₂‐electrode‐based photoelectrochemical cells. Inspired by excellent directional charge transport and the well‐known electroconductibility of 1D anatase TiO₂ nanostructured materials and graphene, respectively, planting ordered, single‐crystalline anatase TiO₂ nanorod clusters on graphene sheets (rGO/ATRCs) via a facial one‐pot solvothermal method is reported. The hierarchical rGO/ATRCs nanostructure can serve as an efficient light‐harvesting electrode for dye‐sensitized solar cells. In addition, the obtained high‐crystallinity anatase TiO₂ nanorods in rGO/ATRCs possess a lower density of trap states, thus facilitating diffusion‐driven charge transport and suppressing electron recombination. Moreover, the novel architecture significantly enhances the trap‐free charge diffusion coefficient, which contributes to superior electron mobility properties. By virtue of more efficient charge transport and higher energy conversion efficiency, the rGO/ATRCs developed in this work show significant advantages over conventional rGO–TiO₂ nanoparticle counterparts in photoelectrochemical cells.     

Polymer Solar Cells with 90% External Quantum Efficiency Featuring an Ideal Light‐ and Charge‐Manipulation Layer

Rapid progress in the power conversion efficiency (PCE) of polymer solar cells (PSEs) is beneficial from the factors that match the irradiated solar spectrum, maximize incident light absorption, and reduce photogenerated charge recombination. To optimize the device efficiency, a nanopatterned ZnO:Al₂O₃ composite film is presented as an efficient light‐ and charge‐manipulation layer (LCML). The Al₂O₃ shells on the ZnO nanoparticles offer the passivation effect that allows optimal electron collection by suppressing charge‐recombination loss. Both the increased refractive index and the patterned deterministic aperiodic nanostructure in the ZnO:Al₂O₃ LCML cause broadband light harvesting. Highly efficient single‐junction PSCs for different binary blends are obtained with a peak external quantum efficiency of up to 90%, showing certified PCEs of 9.69% and 13.03% for a fullerene blend of PTB7:PC₇₁BM and a nonfullerene blend, FTAZ:IDIC, respectively. Because of the substantial increase in efficiency, this method unlocks the full potential of the ZnO:Al₂O₃ LCML toward future photovoltaic applications.     

染料敏化太阳电池用一维纳米结构氧化物光阳极薄膜的研究进展

染料敏化太阳能电池(DSC)由于其工艺简单、成本低廉、理论光电转换效率高,逐渐成为硅基太阳能电池的有力竞争者.DSC电池的光阳极主要起到对染料分子中激发出来的电子进行传导的作用,其光阳极薄膜大多数是由氧化物纳米晶制备的.氧化物纳米晶存在大量界面电阻,导致能量势垒,从而使染料分子中光生电子-空穴对不能有效分离,制约了DSC电池光电转换效率的提高.而高长径比的一维氧化物纳米光阳极薄膜有望降低界面电阻,促进电子-空穴对的有效分离,将是DSC电池光阳极材料开发的重要发展方向.详细论述了染料敏化太阳电池用一维纳米氧化物光阳极薄膜的研究进展.     

Ferroelectric BiFeO3 as an Oxide Dye in Highly Tunable Mesoporous All‐Oxide Photovoltaic Heterojunctions

As potential photovoltaic materials, transition‐metal oxides such as BiFeO₃ (BFO) are capable of absorbing a substantial portion of solar light and incorporating ferroic orders into solar cells with enhanced performance. But the photovoltaic application of BFO has been hindered by low energy‐conversion efficiency due to poor carrier transport and collection. In this work, a new approach of utilizing BFO as a light‐absorbing sensitizer is developed to interface with charge‐transporting TiO₂ nanoparticles. This mesoporous all‐oxide architecture, similar to that of dye‐sensitized solar cells, can effectively facilitate the extraction of photocarriers. Under the standard AM1.5 (100 mW cm^?2) irradiation, the optimized cell shows an open‐circuit voltage of 0.67 V, which can be enhanced to 1.0 V by tailoring the bias history. A fill factor of 55% is achieved, which is much higher than those in previous reports on BFO‐based photovoltaic devices. The results provide here a new viable approach toward developing highly tunable and stable photovoltaic devices based on ferroelectric transition‐metal oxides.     

Towards Optimization of Materials for Dye‐Sensitized Solar Cells

Dye‐sensitized solar cells (DSCs) have received widespread attention owing to their low cost, easy fabrication, and relatively high solar‐to‐electricity conversion efficiency. Based on the nanocrystalline TiO₂ electrode, Ru‐polypyridyl‐complex dye, liquid electrolyte with I^?/I₃^? redox couple, and Pt counter electrode, DSCs have already exhibited an efficiency above 11% and offer an appealing alternative to conventional solar cells. However, further improvements in the efficiency and stability are still required to drive forward practical application. These improvements require the cooperative optimization of the component materials, structures, and processing techniques. In this Research News article, recent progress in DSCs made by our group are reviewed, including some novel approaches to the synthesis of solid‐state and environmentally friendly electrolytes, the fabrication of alternative low‐cost nanostructural electrodes, and the control of recombination at the interfaces.     

量子点敏化太阳能电池对电极材料的研究进展

量子点敏化太阳能电池(Quantum Dot-Sensitized Solar cells, QDSCs)制备工艺简单, 制造成本低廉, 是一种有希望的新型太阳能电池。QDSCs利用量子点具有光谱吸收强、尺寸可调和多激子效应等优点, 能够提高其光电转换效率; 同时, 利用无机量子点替代染料作为敏化剂, 能够解决染料敏化太阳能电池(DSCs)的稳定性问题。但是, QDSCs光电转换效率较低是制约其应用的主要问题。近年来, 通过改变和调控对电极的材料和电子特性提高QDSCs的光电效率的方法受到了广泛关注。本文综述了QDSCs对电极材料的制备方法、微观形貌和晶体结构; 重点分析了金属化合物、复合材料、杂化材料、多元金属硫族化合物、导电聚合物和碳材料对电极对量子点敏化太阳能电池的电荷转移阻抗、光电性能等参数的影响; 并分析影响其电催化活性和电子传输性能的主要因素。最后, 提出通过表面修饰、复合和杂化等方法构筑新型对电极材料, 进而改善和提高QDSCs转换效率和稳定性, 是今后的研究重点和研究方向。     

Ultrafast Flame Annealing of TiO2 Paste for Fabricating Dye‐Sensitized and Perovskite Solar Cells with Enhanced Efficiency

Mesoporous TiO₂ nanoparticle (NP) films are broadly used as electrodes in photoelectrochemical cells, dye‐sensitized solar cells (DSSCs), and perovskite solar cells (PSCs). State‐of‐the‐art mesoporous TiO₂ NP films for these solar cells are fabricated by annealing TiO₂ paste‐coated fluorine‐doped tin oxide glass in a box furnace at 500 °C for ≈30 min. Here, the use of a nontraditional reactor, i.e., flame, is reported for the high throughput and ultrafast annealing of TiO₂ paste (≈1 min). This flame‐annealing method, compared to conventional furnace annealing, exhibits three distinct benefits. First, flame removes polymeric binders in the initial TiO₂ paste more completely because of its high temperature (≈1000 °C). Second, flame induces strong interconnections between TiO₂ nanoparticles without affecting the underlying transparent conducting oxide substrate. Third, the flame‐induced carbothermic reduction on the TiO₂ surface facilitates charge injection from the dye/perovskite to TiO₂. Consequently, when the flame‐annealed mesoporous TiO₂ film is used to fabricate DSSCs and PSCs, both exhibit enhanced charge transport and higher power conversion efficiencies than those fabricated using furnace‐annealed TiO₂ films. Finally, when the ultrafast flame‐annealing method is combined with a fast dye‐coating method to fabricate DSSC devices, its total fabrication time is reduced from over 3 h to ≈10 min.     

Enhanced conversion efficiency of quasi solid state dye sensitized solar cells based on functionalized multi-walled carbon nanotubes incorporated TiO<Subscript>2</Subscript> photoanode

A series of quasi solid state dye sensitized solar cells were fabricated based on the different weight% of MWCNT@TiO₂ photoanode. The MWCNT@TiO₂ nanocomposites were synthesized by simple wet impregation method. The incorporation of MWCNT into the TiO₂ was confirmed by X-ray diffraction, energy dispersive X-ray spectrum and UV–visible spectroscopy. The morphological properties of the nanocomposites were analyzed by transmission electron microscopic analysis. The performance of the quasi solid state dye sensitized solar cell depends solely on the MWCNT content of the photoanode, as the same PVA polymer gel electrolyte has been used. Compared to the conventional TiO₂ photoanode based DSSCs 0.05 wt% MWCNT containing photoanode provide the maximum short circuit current density and the photo conversion efficiency of 9.811 mA/cm^?2 and 3.59 %. The introduction of MWCNT into the TiO₂ results in the rapid electron transport in the photoanode by forming a conductive network due to which improvement in the short circuit current was observed.     

Rose bengal-sensitized nanocrystalline ceria photoanode for dye-sensitized solar cell application

For efficient charge injection and transportation, wide bandgap nanostructured metal oxide semiconductors with dye adsorption surface and higher electron mobility are essential properties for photoanode in dye-sensitized solar cells (DSSCs). TiO₂-based DSSCs are well established and so far have demonstrated maximum power conversion efficiency when sensitized with ruthenium-based dyes. Quest for new materials and/or methods is continuous process in scientific investigation, for getting desired comparative results. The conduction band (CB) position of CeO₂ photoanode lies below lowest unoccupied molecular orbital level (LUMO) of rose bengal (RB) dye. Due to this, faster electron transfer from LUMO level of RB dye to CB of CeO₂ is facilitated. Recombination rate of electrons is less in CeO₂ photoanode than that of TiO₂ photoanode. Hence, the lifetime of electrons is more in CeO₂ photoanode. Therefore, we have replaced TiO₂ by ceria (CeO₂) and expensive ruthenium-based dye by a low cost RB dye. In this study, we have synthesized CeO₂ nanoparticles. X-ray diffraction (XRD) analysis confirms the formation of CeO₂ with particle size ～7 nm by Scherrer formula. The bandgap of 2.93 eV is calculated using UV–visible absorption data. The scanning electron microscopy (SEM) images show formation of porous structure of photoanode, which is useful for dye adsorption. The energy dispersive spectroscopy is in confirmation with XRD results, confirming the presence of Ce and O in the ratio of 1:2. UV–visible absorption under diffused reflectance spectra of dye-loaded photoanode confirms the successful dye loading. UV–visible transmission spectrum of CeO₂ photoanode confirms the transparency of photoanode in visible region. The electrochemical impedance spectroscopy analysis confirms less recombination rate and more electron lifetime in RB-sensitized CeO₂ than TiO₂ photoanode. We found that CeO₂ also showed with considerable difference between dark and light DSSCs performance, when loaded with RB dye. The working mechanism of solar cells with fluorine-doped tin oxide (FTO)/CeO₂/RB dye/carbon-coated FTO is discussed. These solar cells show V _OC ～360 mV, J _SC ～0.25 mA cm ^?2 and fill factor ～63% with efficiency of 0.23%. These results are better as compared to costly ruthenium dye-sensitized CeO₂ photoanode.