Search query: Mercaptophosphonic acids as efficient linkers in quantum dot sensitized solar cells

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abstract: Control over the deposition of quantum dots (QDs) on nanostructured semiconductors is very important for the photovoltaic performance of QD sensitized solar cells. The best control is typically achieved using bifunctional molecular linkers, such as mercaptopropionic acid (MPA) to attach the QDs to metal oxides in a specific manner; however some materials, such as ZnO, are not compatible with these molecules due to their pH sensitivity. We have developed new linkers, mercaptophosphonic acids of different length, which allow efficient functionalization of ZnO nanowires and also mesoporous TiO2 without damaging their surface. Detailed XPS and contact angle studies of the mechanism of self assembly of these acids show that their strong chelation of the oxide surface prevents protonic attack and etching. Using these linkers, we show that colloidal ternary quantum dots, CuInS2, can be conformally and homogeneously deposited on the functionalized metal oxides. Photophysical studies by means of time resolved photoluminescence spectroscopy confirm efficient electron transfer from the QDs to the metal oxides with the rate and efficiency scaling with respect to the linker length and nature. The efficiency of the QD sensitized solar cells fabricated with such assemblies also strongly depends on the linkers used and follows the trends observed for the charge transfer.
author_names: Dmitry Aldakov

Muhammad T Sajjad

Valentina Ivanova

Ashu Kumar Bansal

Jinhyung Park

Peter Reiss

Ifor D W Samuel
title: Mercaptophosphonic acids as efficient linkers in quantum dot sensitized solar cells
year: 2015

abstract: Abstract CuInS2 (CIS) based solar cell devices are fabricated by sensitizing TiO2 photoanodes with CIS quantum dots (CIS QDs) Morphologically different TiO2, viz. Degussa P25 nanoparticles, smooth and fibrous microspheres (SmS and FmS respectively) are used to fabricate photoanodes. CIS QDs are synthesized using dodecanethiol (DDT) CuI and In(OAc)3 precursors by solvothermal method. DDT surfactant present on the CIS QDs surface is replaced with 3 mercaptopropionic acid in a single phase one step procedure to enable efficient loading of QDs onto photoanode and as linker molecule for charge carrier extraction. The CIS QDs sensitized on SmS and FmS microsphere photoanode layers exhibit a photoconversion efficiency (e) of 3.2% and 1.6% respectively, in comparison to e 2.1% for nanoparticulate TiO2 (Degussa P25) Further increase in efficiency is obtained (3.8% for SmS and 2.5% for FmS) when composite photoanode films made of porous microspheres filled with nanoparticulate P25 are used. A maximum efficiency of 3.8% (with JSC 6.2 mA, VOC 926 mV and FF 66 for cell area 0.25 cm2 and thickness 20 um) is realized when 4.6 nm CIS QDs sensitized on composite photoanode (consisting of 80 wt. SmS and 20 wt. P25) is used. High VOC observed is unprecedented and is possible due to combined effect of SmS+P25 composite photoanode properties such as fewer defects, good connectivity between particles, effective light scattering, minimum recombination, and effective electron transport and size optimized CuInS2 QDs. Electrochemical impedance spectroscopy studies reveal a low interfacial resistance and longer electron life time in SmS+P25 composite photoanodes.
author_names: P Ilaiyaraja

Benadict Rakesh

Tapan Kumar Das

Pavana S V Mocherla

C Sudakar
title: CuInS2 quantum dot sensitized solar cells with high VOC 0.9 V achieved using microsphere nanoparticulate TiO2 composite photoanode
year: 2018

abstract: Searching suitable panchromatic QD sensitizers for expanding the light harvesting range, accelerating charge separation, and retarding charge recombination is an effective way to improve power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs) One possible way to obtain a wide absorption range is to use the exciplex state of a type II core/shell structured QDs. In addition, this system could also provide a fast charge separation and low charge recombination rate. Herein, we report on using a CdTe/CdSe type II core/shell QD sensitizer with an absorption range extending into the infrared region because of its exciplex state, which is covalently linked to TiO2 mesoporous electrodes by dropping a bifunctional linker molecule mercaptopropionic acid (MPA) capped QD aqueous solution onto the film electrode. High loading and a uniform distribution of QD sensitizer throughout the film electrode thickness have been confirmed by energy dispersive X ray (EDX) elemental mapping. The accelerated electron injection and retarded charge recombination pathway in the built CdTe/CdSe QD cells in comparison with reference CdSe QD based cells have been confirmed by impedance spectroscopy, fluorescence decay, and intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) analysis. With the combination of the high QD loading and intrinsically superior optoelectronic properties of type II core/shell QD (wide absorption range, fast charge separation, and slow charge recombination) the resulting CdTe/CdSe QD based regenerative sandwich solar cells exhibit a record PCE of 6.76% (J(sc) 19.59 mA cm( 2) V(oc) 0.606 V, and FF 0.569) with a mask around the active film under a full 1 sun illumination (simulated AM 1.5) which is the highest reported to date for liquid junction QDSCs.
author_names: Jian-Jun Wang

Ivan Mora-Sero

Zhenxiao Pan

Ke Zhao

Hua Zhang

Yaoyu Feng

Guocheng Yang

Xinhua Zhong

Juan Bisquert
title: Core/shell colloidal quantum dot exciplex states for the development of highly efficient quantum dot sensitized solar cells.
venue: Journal of the American Chemical Society
year: 2013

abstract: This paper reports a facile and environmentally friendly approach to the preparation of highly efficient quantum dot sensitized solar cells (QDSSCs) based on a combination of aqueous CuInS2 quantum dots (QDs) and thiol coadsorbents. The photovoltaic properties of the QDSSCs were found to be dependent on the type and concentration of the thiol coadsorbent. The incorporation of thiol coadsorbents results in improved JSC and VOC because (1) they provide disulfide reductants during the QD sensitization process and (2) the coadsorbent molecules are anchored on the TiO2 surface, thus affecting the movement of the conduction band of TiO2. To the best of the our knowledge, this is the first demonstrated use of various thiol coadsorbents as reducing agents in the fabrication of high efficiency QDSSCs. CuInS2 QDSSCs fabricated with the assistance of thioglycolic acid coadsorbents exhibited efficiencies as high as 5.90% which is 20 times higher than that of the control device without thiol coadsorbents (0.29% In addition, the photovoltaic properties of a device fabricated using the colloidal CuInS2 QDs coated with different bifunctional linkers were investigated for comparison. The versatility of this facile fabrication process was demonstrated in the preparation of solar cells sensitized with aqueous AgInS2 or CdSeTe QDs. The AgInS2 QDSSC showed a conversion efficiency of 2.72% which is the highest reported for Ag based metal sulfides QDSSCs thus far.
author_names: Jia-Yaw Chang

Chen-Hei Li

Ya-Han Chiang

Chia-Hung Chen

Peihang Li
title: Toward the Facile and Ecofriendly Fabrication of Quantum Dot Sensitized Solar Cells via Thiol Coadsorbent Assistance.
venue: ACS applied materials interfaces
year: 2016

abstract: A modified polysulfide redox couple, (CH(3)(4)N](2)S/(CH(3)(4)N](2)S(n) in an organic solvent (3 methoxypropionitrile) was employed in CdS quantum dot (QD) sensitized solar cells (QDSSCs) and an unprecedented energy conversion efficiency of up to 3.2% was obtained under AM 1.5 G illumination. The QDs were linked to nanoporous TiO(2) via covalent bonds by using thioglycolic acid, and chemical bath deposition in an organic solvent was then used to prepare the QDSSCs, facilitating high wettability and superior penetration capability of the TiO(2) films. A very high fill factor of 0.89 was observed with the optimized QDSSCs.
author_names: Lisheng Li

Xichuan Yang

Jiajia Gao

Haining Tian

Jianzhang Zhao

Anders Hagfeldt

Licheng Sun
title: Highly efficient CdS quantum dot sensitized solar cells based on a modified polysulfide electrolyte.
venue: Journal of the American Chemical Society
year: 2011

abstract: We report on an interesting and efficient one step linker assisted chemical bath deposition method to synthesise CdTe or CdTe/CdS quantum dot sensitized TiO2 photoelectrodes. The CdTe or CdTe/CdS core/shell quantum dots with different size and structure can be easily obtained by controlling the hydrothermal temperature. The QDs are covalently linked to TiO2 nanocrystallites by thioglycolic acid (TGA) bifunctional molecule which also acts as stabilizer and sulfur source in this one step fabrication. In this sensitized electrode, CdTe has higher light absorptivity while the CdS shell plays a crucial role in the sensitive CdTe QDs protection and photo generated charges separation. Both effects push the power conversion efficiency of the quantum dot sensitized solar cells (QDSSCs) up to 3.8% and 5.25% under AM 1.5 G one sun (100 mW cm 2) and 0.12 sun illumination, respectively.
author_names: Xiaoyun Yu

Bingxin Lei

Dai-Bin Kuang

Chengyong Su
title: Highly efficient CdTe/CdS quantum dot sensitized solar cells fabricated by a one step linker assisted chemical bath deposition
year: 2011

abstract: Abstract This paper presents a facile approach to prepare highly efficient CdSe(S) quantum dots (QDs) sensitized TiO 2 photoanodes. Aqueous colloidal CdSe(S) QDs were synthesized and simultaneously assembled onto TiO 2 mesoporous films through a one step hydrothermal route with the aid of thioglycolic acid. This sensitization strategy involves the combination of linker assisted assembly with in situ fabrication. It achieves high coverage and uniform distribution of CdSe(S) QDs within mesoporous TiO 2 films, while keeping strong electronic coupling between QDs and the TiO 2 substrate. The effect of the molar ratios of the ligands (thioglycolic acid) to monomers (Cd 2+ ions) on the cell performance was investigated, and the experimental results showed that the cell based on the photoanode prepared at [ligand][monomer] 3.6 achieved a maximum short circuit current density of 10.51 mA cm 2 and a power conversion efficiency of 1.97% under one sun illumination (AM 1.5 G, 100 mW cm 2
author_names: Xiaohui Song

Minqiang Wang

Yanhua Shi

Jianping Deng

Zhi Yang

Xiuchao Yao
title: In situ hydrothermal growth of CdSe(S) nanocrystals on mesoporous TiO2 films for quantum dot sensitized solar cells
year: 2012

abstract: Presynthesized high quality CdS/CdSe inverted type I core/shell structure QDs have been deposited onto TiO(2) electrodes after first coating with bifunctional linker molecules, mercaptopropionic acid (MPA) and the resulting quantum dot sensitized solar cells (QDSCs) exhibited record conversion efficiency of 5.32% (V(oc) 0.527 V, J(sc) 18.02 mA/cm(2) FF 0.56) under simulated AM 1.5, 100 mW cm( 2) illumination. CdS/CdSe QDs with different CdSe shell thicknesses and different corresponding absorption onsets were prepared via the well developed organometallic high temperature injection method. MPA capped water dispersible QDs were then obtained via ligand exchange from the initial organic ligand capped oil dispersible QDs. The QD sensitized TiO(2) electrodes were facilely prepared by pipetting the MPA capped CdS/CdSe QD aqueous solution onto the TiO(2) film, followed by a covering process with a ZnS layer and a postsintering process at 300 degC. Polysulfide electrolyte and Cu(2)S counterelectrode were used to provide higher photocurrents and fill factors of the constructed cell devices. The characteristics of these QDSCs were studied in more detail by optical measurements, incidental photo to current efficiency measurements, and impedance spectroscopy. With the combination of the modified deposition technique with use of linker molecule MPA capped water soluble QDs and well developed inverted type I core/shell structure of the sensitizer together with the sintering treatment of QD bound TiO(2) electrodes, the resulting CdS/CdSe sensitized solar cells show a record photovoltaic performance with a conversion efficiency of 5.32%
author_names: Zhenxiao Pan

Hua Zhang

Kan Cheng

Yumei Hou

Jianli Hua

Xinhua Zhong
title: Highly efficient inverted type I CdS/CdSe core/shell structure QD sensitized solar cells.
venue: ACS nano
year: 2012

abstract: Quantum dot solar cells (QDSCs) have attracted great interest as a next generation solar energy conversion system. 1 While the conversion efficiency of QDSCs has recently exceeded 5% they still lag behind their dye sensitized solar cell analogues. The performance of QDSCs is governed by many factors such as their light harvesting capacity, interfacial charge recombination, the characteristics of the electrolytes, and the electrocatalytic activity of the counter electrode. 2 Among them, the anode characteristics (i.e. light absorption and charge recombination) are intimately associated with the deposition method of the QD sensitizer. Therefore, the development of an effective deposition method is of great importance for highly efficient solar cell fabrication. Commonly used deposition methods include chemical bath deposition (CBD) successive ionic layer adsorption and reaction (SILAR) a molecular linker based approach (MBA) and direct adsorption (DA) 3 CBD and SILAR are
author_names: Hye Mi Choi

In Ae Ji

Jin Ho Bang
title: Quantum Dot Solar Cells Prepared Using Electrophoretic Deposition
year: 2013

abstract: Quantum dot sensitized solar cells (QDSSCs) are becoming a viable alternative in the market of the third generation solar cells. Replacing conventional TiO2 or ZnO thin films with anatase TiO2 nanotubes (NTs) leads to a faster charge separation of the excited electron from the quantum dot (QD) to the anode and, consequently, to higher efficiencies. In addition, the adsorption mode of the QDs to the nanotube plays a significant role in the quest for more efficient QDSSCs. We investigate these effects by means of density functional theory (DFT) and real time time dependent DFT. Differently sized QDs (CdSe)13 and (CdSe)34, bare clusters and saturated with methylamine and p toluidine] are added to different anatase TiO2 nanotubes [NT(0,8) NT(0,12) NT(0,16) We considered direct adsorption or linkage via mercaptopropionic acid (MPA) First, the nanotube diameter does not affect the electronic absorption spectra. When the QDs are linked with MPA, we find that the absorption spectrum resembles that of the single QD. Also, the size of the QD has a significant impact on the absorption spectrum and it can happen that the conduction band (CB) of an unsaturated QD lies below that of the nanotube. Saturation of the QD's surface pushes the CB up again. Furthermore, aromatic ligands increase the first absorption peak maximum to higher energies.
author_names: Roger Nadler

Javier Fernandez Sanz
title: TiO2 nanotubes sensitized with CdSe quantum dots
venue: Theoretical Chemistry Accounts
year: 2018