Highly efficient CdS/CdSe-sensitized solar cells controlled by the structural properties of compact porous TiO2 photoelectrodes

At present, the photovoltaic performance of quantum dot-sensitized solar cells (QDSCs) is still much lower than conventional DSCs. Appropriate porous TiO(2) photoanodes for QDSCs need to be further investigated, and optimization of the nanoparticle-based photoanodes is highly desirable as well. In this article, the influence of the structural properties of various TiO(2) photoanodes on CdS/CdSe-sensitized solar cells have been systematically studied. Quantitative analyses of light-harvesting efficiency (LHE) and electron-transfer yield (Φ(ET)) for the QDSCs are investigated for the first time. It is revealed that the LHE increases in the long wavelength region with the addition of large size TiO(2) particles to the transparent film. In the meantime, the balance between the light scattering and surface area also needs to be controlled, which can significantly restrain the dark current of the device. A double-layer photoanodic structure can give 4.92% of light-to-electricity conversion efficiency with a photoactive area of 0.15 cm(2).     

A sulfide/polysulfide-based ionic liquid electrolyte for quantum dot-sensitized solar cells

Further development of quantum dot-sensitized solar cells (QDSCs) will require long-term stability in addition to the continuous increase of photovoltaic (PV) conversion efficiency achieved in the last years. We report a robust S(2-)/S(n)(2-) electrolyte that has been specifically designed for compatibility with CdSe quantum dots in sensitized solar cells. The new pyrrolidinium ionic liquid reaches 1.86% efficiency and a short-circuit current close to 14 mA·cm(-2) under air-mass 1.5 global illumination and improves the device lifetime with good photoanode stability over 240 h. PV characterization showed that the solar cell limitations relate to poor catalysis of regeneration at the counter electrode and high recombination. Further improvement of these factors in the robust electrolyte configuration may thus have a significant impact for advancing the state-of-the-art in QDSCs.     

Ultimate Charge Extraction of Monolayer PbS Quantum Dot for Observation of Multiple Exciton Generation

Multiple exciton generation (MEG) has great potential to improve the Shockley-Queisser (S-Q) efficiency limitation for colloidal quantum dot (CQD) solar cells. However, MEG has rarely been observed in CQD solar cells because of the loss of carriers through the transport mechanism between adjacent QDs. Herein, we demonstrate that excess charge carriers produced via MEG can be efficiently extracted using monolayer PbS QDs. The monolayer PbS QDs solar cells exhibit α=1 in the light intensity dependence of the short-circuit current density J_sc (J_sc∝I^α) and an internal quantum efficiency (IQE) value of 100 % at 2.95 eV because of their very short charge extraction path. In addition, the measured MEG threshold is 2.23 times the bandgap energy (E_g), which is the lowest value in PbS QD solar cells. We believe that this approach can provide a simple method to find suitable CQD materials and design interface engineering for MEG.     

Graphene quantum dots assisted photovoltage and efficiency enhancement in CdSe quantum dot sensitized solar cells

CdSe quantum dot sensitized solar cells(QDSCs) modified with graphene quantum dots(GQDs) have been successfully achieved in this work for the first time. Satisfactorily, the optimized photovoltage(Voc) of the modified QDSCs was approximately 0.04 V higher than that of plain CdSe QDSCs, consequently improving the photovoltaic performance of the resulting QDSCs. Served as a novel coating on the CdSe QD sensitized photoanode, GQDs played a vital role in improving Vocdue to the suppressed charge recombination which has been confirmed by electron impedance spectroscopy as well as transient photovoltage decay measurements. Moreover, different adsorption sequences, concentration and deposition time of GQDs have also been systematically investigated to boost the power conversion efficiency(PCE) of CdSe QDSCs. After the coating of CdSe with GQDs, the resulting champion CdSe QDSCs exhibited an improved PCE of 6.59% under AM 1.5G full one sun illumination.     

Ag2S quantum dot-sensitized WO3 photoelectrodes for solar cells

This work investigates the photovoltaic properties of new-architecture Ag₂S quantum dot-sensitized solar cells (QDSCs) fabricated on WO₃ electrodes. Liquid-junction Ag₂S QDSCs were fabricated from QDs synthesized using the successive ionic layer adsorption and reaction process. The optimal QDSC yielded an efficiency η of 0.20 % under a 100-mW/cm² light illumination. Coating the QDSC with a compact layer and a scattering layer improved η to 0.31 % with a short-circuit current density J _sc of 5.81 mA/cm² and an open-circuit voltage V _oc of 0.21 V. η increased to 0.53 % at a reduced 0.1 sun illumination with a J _sc of 1.11 mA/cm². The external quantum efficiency (EQE) spectrum covered the spectral range of 350–900 nm with a maximal EQE of 29 % at λ?=?650 nm. This work demonstrates the feasibility of the new-configuration Ag₂S QDSCs fabricated on WO₃ electrodes.     

用CdSe/ZnS量子点提高体异质结有机太阳电池的效率

通过掺杂吸收光谱在可见光波段的量子点可提高聚合物对可见光的吸收,因此掺杂CdSe/ZnS核-壳结构量子点(CQDs)能提高聚(3-己基噻吩):[6,6]-苯基-C61-丁酸甲酯(P3HT:PCBM)体异质结太阳电池的能量转换效率.本文研究了CdSe/ZnS量子点在P3HT:PCBM中的不同掺杂比例及其表面配体对太阳电池光伏性能的影响,优化器件ITO(氧化铟锡)/PEDOT:PSS(聚(3,4-乙撑二氧噻吩:聚苯乙烯磺酸)/P3HT:PCBM:(CdSe/ZnS)/Al的能量转换效率达到了3.99%,与相同条件下没有掺杂量子点的参考器件ITO/PEDOT:PSS/P3HT:PCBM/Al相比,其能量转换效率提高了45.1%.     

A solid-state CdSe quantum dot sensitized solar cell based on a quaterthiophene as a hole transporting material

A hybrid quantum dot sensitized solar cell (QDSC) composed of CdSe quantum dots (QDs) as light harvesters and TiO(2) and 3,3'-didodecyl-quaterthiophene (QT12) as electron and hole conductors, respectively, has been fully processed in air. The sensitizer has been introduced into the TiO(2) nanoporous layer either by the successive ionic layer adsorption and reaction method or by attaching colloidal QDs either directly or through molecular cables (linkers). As previously observed for QDSCs based on liquid electrolytes, the efficiency depends on the way of QD attachment, the direct adsorption of QDs being the procedure yielding the best results. Thermal annealing was applied in order to enhance the device response under illumination. Remarkable open circuit potentials are attained (close to 1 V), leading to an efficiency of 0.34% (AM 1.5G) in initial tests. Although low, it ranks as one of the highest values reported for solid state QDSCs based on titanium dioxide and colloidal quantum dots.     

贫PbI2基体的胶体量子点固体用于高效红外太阳能电池(英文)

胶体量子点(CQD)具有优异的红外光吸收能力和光谱可调特性,是用于制备高效太阳能电池最有前途的红外光电材料之一。然而,以醋酸铵(AA)为添加剂的液相配体交换会导致CQD固体中产生宽带隙PbI₂基质,其将作为电荷传输势垒,在很大程度上影响了CQD太阳能电池(CQDSC)中载流子的提取,从而影响了光伏性能。本文报道利用二甲基碘化铵(DMAI)调节CQD配体交换过程,使载流子在CQD固体中的传输势垒大幅降低。通过对CQD固体进行全面的表征和理论计算,充分揭示了DMAI和CQD之间的相互作用。结果表明,通过DMAI调节CQD配体交换过程,使CQD固体均匀堆积,提高了载流子输运性能,并且陷阱辅助复合受到显著抑制。因此,CQDSC器件中的载流子提取得到了大幅提高,能量转换效率(PCE)比用AA制备的CQDSC器件提高了17.8%。此工作为调控CQD表面化学特性提供了新的研究思路,并为降低CQD固体中载流子输运的势垒提供了可行的方法。     

TiO2微球的合成及其作为散射层在量子点敏化太阳能电池中的应用

以十六烷基三甲基溴化铵（CTAB）为模板剂,通过TiCl₄在乙醇水溶液中的直接水解,制备了介孔TiO₂微球. X射线衍射（XRD）结果表明所制备的微球晶型为金红石,扫描电镜（SEM）结果显示微球的直径大约为700 nm,由粒径约为16 nm的小颗粒堆积而成. 通过刮涂法制备了在TiO₂小颗粒层上涂覆有作为散射层的TiO₂微球和未涂覆微球的薄膜. 并通过化学浴沉积（CBD）的方法在膜上生长CdS/CdSe量子点,得到了量子点敏化太阳能电池（QDSCs）. 紫外吸收和漫反射结果表明,这种微球结构有利于量子点的沉积,具有较强的光散射作用,有效地增加了光线的收集,从而提高了电池的光电流,最终得到了4.5%的光电转换效率,比不加散射层的电池的效率高27.7%,也比利用传统散射层（由20 nm TiO₂ 小颗粒和400 nm TiO₂ 固体颗粒组成）的电池效率高10.2%. 我们把电池效率的提升归因于较强的光散射作用和较长的电子寿命.     

Quantum‐Dot‐Sensitized Solar Cells

Quantum‐dot‐sensitized solar cells (QDSCs) are a promising low‐cost alternative to existing photovoltaic technologies such as crystalline silicon and thin inorganic films. The absorption spectrum of quantum dots (QDs) can be tailored by controlling their size, and QDs can be produced by low‐cost methods. Nanostructures such as mesoporous films, nanorods, nanowires, nanotubes and nanosheets with high microscopic surface area, redox electrolytes and solid‐state hole conductors are borrowed from standard dye‐sensitized solar cells (DSCs) to fabricate electron conductor/QD monolayer/hole conductor junctions with high optical absorbance. Herein we focus on recent developments in the field of mono‐ and polydisperse QDSCs. Stability issues are adressed, coating methods are presented, performance is reviewed and special emphasis is given to the importance of energy‐level alignment to increase the light to electric power conversion efficiency.     

An efficient method to prepare high-performance dye-sensitized photoelectrodes using ordered TiO<Subscript>2</Subscript> nanotube arrays and TiO<Subscript>2</Subscript> quantum dot blocking layers

High-performance dye-sensitized photoelectrodes using ordered TiO₂ nanotube arrays (TNTs) and TiO₂ quantum dot blocking layers are fabricated. The free-standing TNT membranes with perfect ordered morphology are prepared by three times of anodic oxidation on Ti foils. These TNT membranes can be easily transported to conductive glasses to fabricate front-side illuminated photoelectrodes. By changing anodic oxidation duration, the thickness of TNT membranes can be controlled, which shows significant influence on the UV-Vis reflectance and absorption abilities of TNT-based photoelectrodes and further influence photovoltaic performance of dye-sensitized solar cells (DSSCs). The highest power conversion efficiency (PCE) of DSSCs about 6.21 % can be obtained by using TNT membranes prepared with anodic oxidation of 3 h. For further improving photovoltaic performance of DSSCs, TiO₂ quantum dot (QDs) blocking layers are inserted between conductive glasses and TNT membranes in the photoelectrodes, which show remarkable effects. The highest PCE of DSSCs with this kind of blocking layers can increase to 8.43 %, producing 35.75 % enhancement compared with that of the counterparts without TiO₂ QD blocking layers.     

Energy Relay from an Unconventional Yellow Dye to CdS/CdSe Quantum Dots for Enhanced Solar Cell Performance

A new design for a quasi‐solid‐state Forster resonance energy transfer (FRET) enabled solar cell with unattached Lucifer yellow (LY) dye molecules as donors and CdS/CdSe quantum dots (QDs) tethered to titania (TiO₂) as acceptors is presented. The Forster radius is experimentally determined to be 5.29 nm. Sequential energy transfer from the LY dye to the QDs and electron transfer from the QDs to TiO₂ is followed by fluorescence quenching and electron lifetime studies. Cells with a donor–acceptor architecture (TiO₂/CdS/CdSe/ZnS‐LY/S^2?‐multi‐walled carbon nanotubes) show a maximum incident photon‐to‐current conversion efficiency of 53 % at 530 nm. This is the highest efficiency among Ru‐dye free FRET‐enabled quantum dot solar cells (QDSCs), and is much higher than the donor or acceptor‐only cells. The FRET‐enhanced solar cell performance over the majority of the visible spectrum paves the way to harnessing the untapped potential of the LY dye as an energy relay fluorophore for the entire gamut of dye sensitized, organic, or hybrid solar cells.     

Synthesis of new nanocrystal-polymer nanocomposite as the electron acceptor in polymer bulk heterojunction solar cells

A hydroxyl-coated CdSe nanocrystal (CdSe-OH) and a CdSe-polymer nanocomposite were synthesized and used as the electron acceptors in polymer solar cells (PSCs). The CdSe-polymer composite was prepared via atom transfer radical polymerization (ATRP) of N-vinylcarbazole on functionalized CdSe quantum dots. Physical properties and photovoltaic characteristics of the CdSe-poly(N-vinylcarbazole) (CdSe-PVK) nanocomposite have been investigated. Thermogravimetric analysis (TGA) results displayed higher thermal stability for CdSe-PVK nanohybrid in comparison with the linear-type PVK polymer. Differential scanning calorimetry (DSC) studies indicated that CdSe-PVK had a lower glass-transition temperature (T_g) in comparison with PVK due to the branch effect of the star-shaped polymer hybrid. Cyclic voltammetric (CV) measurements were performed to obtain HOMO and LUMO values of PVK and CdSe-PVK. TEM and SEM micrographs exhibited CdSe nanoparticles were well coated with PVK polymer. Both CdSe-OH and CdSe-PVK were blended with poly(3-hexylthiophene) (P3HT) and used as the active layer in bulk heterojunction solar cells. Polymer solar cell based on CdSe-PVK as acceptor revealed that the photovoltaic properties can be significantly improved when PVK polymer chains were grafted on surfaces of CdSe nanocrystals. In comparison with the P3HT:CdSe-OH system, PSC based on P3HT:CdSe-PVK showed an improved power conversion efficiency (0.02% vs. 0.001%). Film topography studied by AFM further confirmed the better device performance was due to the enhanced compatibility between P3HT and CdSe-PVK.     

基于量子点涂料的柔性光阳极及碳基对电极的制备和优化

首先制备出量子点(QDs)/TiO_2涂料,分别采用丝网印刷法与刀刮法将涂料涂覆于ITO/PET柔性基底上,结果表明刀刮法制备量子点敏化太阳电池(QDSCs)效果更佳,且具有普适性。基于铜片对电极所组装的ZnCuInSe,CdSe和CdSeTe量子点半柔性QDSCs最高效率分别达2.83%,2.46%和1.99%。另外,我们对石墨纸进行表面化学修饰以提高亲水性,再通过简单的连续离子交换吸附法(SILAR)在石墨纸上负载Cu_xS纳米粒子,制备出Cu_xS/GP柔性对电极,进一步组装成全柔性QDSCs,获得了2.13%光电转化效率。     

基于量子点涂料的柔性光阳极及碳基对电极的制备和优化

首先制备出量子点（QDs）/TiO₂涂料,分别采用丝网印刷法与刀刮法将涂料涂覆于ITO/PET柔性基底上,结果表明刀刮法制备量子点敏化太阳电池（QDSCs）效果更佳,且具有普适性。基于铜片对电极所组装的ZnCuInSe,CdSe和CdSeTe量子点半柔性QDSCs最高效率分别达2.83%,2.46%和1.99%。另外,我们对石墨纸进行表面化学修饰以提高亲水性,再通过简单的连续离子交换吸附法（SILAR）在石墨纸上负载Cu_xS纳米粒子,制备出Cu_xS/GP柔性对电极,进一步组装成全柔性QDSCs,获得了2.13%光电转化效率。     

Enhanced dispersion of CdSe/MEH-CN-PPV hybrid nanocomposites by in situ polymerization using AEM as photopolymerizable precursor

Colloidal quantum dots (CQDs) can easily become aggregated when blended in a polymer matrix. Although several techniques have been reported to prepare dispersed CQDs in a polymer matrix, the novel approach of this work is to obtain well-dispersed CQD–polymer nanocomposites through the in situ photopolymerization of a third source, thereby broadening the material selection available for such nanocomposites. Therefore, dispersed CQD–polymer nanocomposites were prepared by the photopolymerization of 2-aminoethyl methacrylate hydrochloride (AEM) precursor in a blend of trioctyl phosphine oxide-capped CdSe CQDs and poly(2-methoxy-5-(2′-ethylhexyloxy)-α,α′dicyano-p-xylylidene-alt-2,5-dihexyoxy-p-xylylidene) (MEH-CN-PPV). The photopolymerization of AEM was developed for this work in order to prevent possible decomposition of CQDs induced by introducing metallic catalysts or heat and to eliminate the need for further functionalization of CQDs or polymers. The morphology of the photopolymerized CdSe CQD/MEH-CN-PPV/AEM was corroborated by direct observation of the quantum dot dispersion in the resultant sphere-shaped structures via transmission electron microscopy. Photoluminescence quenching and shorter photoluminescence decay lifetime of the MEH-CN-PPV in the photopolymerized nanocomposite were observed, indicating that the photopolymerized CdSe CQD/MEH-CN-PPV/AEM nanocomposite has an enhanced energy transfer efficiency in comparison to typical aggregated CdSe quantum dot/MEH-CN-PPV nanocomposites as a result of better dispersion.     

Fabrication of carbon quantum dots via ball milling and their application to bioimaging

Carbon quantum dots (CQDs) with an average diameter of 3 nm, exhibiting blue photoluminescence, have been obtained from commercial conductive carbon black by a cost-effective and straightforward exfoliation method using dry ball milling in the presence of sodium carbonate. As a secondary abrasive medium, sodium carbonate provides effective exfoliation of carbon black with a high degree of CQD graphitization and plays an essential role in the functionalization of CQDs with oxygen groups. Due to the low toxicity of CQDs against HeLa cancer cells (cell viability above 90% at a CQD concentration of 200 μg cm⁻³) and the ability to penetrate cells and emit blue light, CQDs are possibly suitable for biological imaging of cells.     

Perovskite-sensitized solar cell utilizing TiO2 nanograss: Effect of dipping time of CH3NH3PbI3 perovskite

Organic perovskite has potential to replace organic dye as light absorber in solar cell since it possesses better optical absorption in visible region than organic dye. This work is concerned with the investigation of the influence of CH₃NH₃PbI₃ perovskite dipping time on the performance of perovskite-sensitized solar cell (PSSC). The effect of the dipping time on the morphology and photoluminescence of the sample has also been investigated. It was found that the device achieved a power conversion efficiency (PCE) as high as 5.57 ± 0.4% at the optimum dipping time of 4 h. The highest PCE is due to the highest IPCE, lowest R_ct and the longest carrier lifetime (τ).     

Effects of processing additives in non-fullerene organic bulk heterojunction solar cells with efficiency >11%

The solar cell surface morphologies with different additives observed with slightly changed in roughness. It is easily to get the best PCE of 11.1% with using 0.5% DIO additives.     

Effective design of A-D-A small molecules for high performance organic solar cells via F atom substitution and thiophene bridge

Three novel small molecules with acceptor-donor-acceptor (A-D-A) configuration, SBDT1, SBDT2 and SBDT3, where 4,8-bis(octyloxy)benzo[1,2-b:4,5-b′]dithiophene (BDT) as the electron-donating core connecting to thiophene-substituted benzothiadiazole (BT) as electron-withdrawing are reported. The effects of fluorine atoms on the photophysical properties by introducing different fluorine atoms into the benzothiadiazole unit were investigated. These SBDTs exhibit good thermal stability, excellent panchromatic absorption in solution and film. SBDT2 and SBDT3 with fluorine-substituted BT possess a relatively deeper the highest occupied molecular orbital (HOMO). These A-D-A type molecules were treated as donor and PC₇₁BM as acceptor in bulk heterojunction (BHJ) small-molecule organic solar cells (SMOSCs). Among them, device based on SBDT2 gave the best device performance with a PCE of 5.06% with J_sc of 10.56 mA/cm², V_oc of 0.85 V, fill factor (FF) of 56.4%. These studies indicate that proper incorporation of fluorine atoms is an effective way to increase the efficiency of organic solar cells.