CdSeTe/CdS Type-I Core/Shell Quantum Dot Sensitized Solar Cells with Efficiency over 9% (original) (raw)
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Thin Solid Films, 2013
CdTe/CdSe and CdSe/CdTe core/shell colloidal quantum dots, both with and without a second CdS shell, have been synthesised and characterised by absorption and photoluminescence spectroscopies, scanning transmission electron microscopy and X-ray diffraction. Each type of quantum dot had a zinc blende crystal structure and had an absorption edge in the near-infrared, potentially enabling the more efficient exploitation of the solar spectrum. Each was used to sensitise a photovoltaic cell of a 'Grätzel-type' design consisting of the dots coated onto mesoporous TiO 2 , a sulphur-based electrolyte and a platinum top electrode. The photovoltaic efficiency of the cells was found to be greater for Type-II dots as compared to the quasi-Type-II dots. However, the efficiency was reduced on the addition of an outer CdS shell indicating that it acts as a barrier to charge extraction.
Nanotechnology, 2008
Colloidal CdSe quantum dots (QDs) of different sizes, prepared by a solvothermal route, have been employed as sensitizers of nanostructured TiO 2 electrode based solar cells. Three different bifunctional linker molecules have been used to attach colloidal QDs to the TiO 2 surface: mercaptopropionic acid (MPA), thioglycolic acid (TGA), and cysteine. The linker molecule plays a determinant role in the solar cell performance, as illustrated by the fact that the incident photon to charge carrier generation efficiency (IPCE) could be improved by a factor of 5-6 by using cysteine with respect to MPA. The photovoltaic properties of QD sensitized electrodes have been characterized for both three-electrode and closed two-electrode solar cell configurations. For three-electrode measurement a maximum power conversion efficiency near 1% can be deduced, but this efficiency is halved in the closed cell configuration mainly due to the decrease of the fill factor (FF).
Energy Environ. Sci., 2012
A high-performance quantum dot-sensitized solar cell (QDSSC) is reported, which consists of a TiO 2 /CuInS 2-QDs/CdS/ZnS photoanode, a polysulfide electrolyte, and a CuS counter electrode. The sensitization process involves attaching presynthesized CuInS 2 QDs (3.5 nm) to a TiO 2 substrate with a bifunctional linker, followed by coating CdS with successive ionic layer adsorption and reaction (SILAR) and ZnS as the last SILAR layer for passivation. This process constructs a sensitizing layer that comprises of CdS nanocrystals, closely packed around the earlier-linked CuInS 2 QDs, which serves as the pillars of the layer. The CuS counter electrode, prepared via successive ionic solution coating and reaction, has a small charge transfer resistance in the polysulfide electrolyte. The QDSSC exhibits a short-circuit photocurrent (J sc) of 16.9 mA cm-2 , an open-circuit photovoltage (V oc) of 0.56 V, a fill factor of 0.45, and a conversion efficiency of 4.2% under one-sun illumination. The heterojunction between the CuInS 2 QDs and CdS extends both the optical absorption and incident photon conversion efficiency (IPCE) spectra of the cell to a longer wavelength of approximately 800 nm, and provides an IPCE of nearly 80% at 510 nm. The high TiO 2 surface coverage of the sensitizers suppresses recombination of the photogenerated electrons. This results in a longer lifetime for the electrons, and therefore, the high V oc value. The notably high J sc and V oc values demonstrate that this sensitization strategy, which exploits the quantum confinement reduction and other synergistic effects of the CuInS 2-QDs/CdS/ZnS heterostructure, can potentially outperform those of other QDSSCs.
ACS Nano, 2011
An in situ electrodeposition method is described to fabricate the CdS or/and CdSe quantum dot (QD) sensitized hierarchical TiO 2 sphere (HTS) electrodes for solar cell application. Intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS) and electrochemical impedance spectroscopy (EIS) measurements are performed to Supporting Information Available: Figure of XRD patterns of CdS and/or CdSe-sensitized TiO 2 films. This material is available free of charge via the Internet at http://pubs.acs.org.
Improvement of Efficiency in CdS Quantum Dots Sensitized Solar Cells
Acta Physica Polonica A, 2013
CdS quantum dots were coated on TiO2 layer by successive ionic layer adsorption and reaction method. An ecient photovoltaic energy conversion and signicant quantum-size eect were observed. The magnitude of the short-circuit photocurrent density JSC was found to be approximately 6.01 mA/cm 2 for graphene oxide-incorporated CdS/TiO2 solar cell, while the JSC of only CdS-sensitized solar cells was lower than 4.40 mA/cm 2. The eciency of the CdS/TiO2 solar cell with a graphene oxide layer containing CdS QDs was 60% higher than that of the CdS/TiO2 solar cell. The cell eciency was remarkably improved with the graphene oxide-incorporation. The carrier recombination of the QDs sensitized solar cells based on CdS-coated TiO2 was signicantly suppressed due to photogenerated charge carrier transports resulting from the presence of graphene oxide.
Tertiary hierarchically structured TiO2 for CdS quantum-dot-sensitized solar cells
A tertiary hierarchically structured mesoporous spherical TiO 2 (with a diameter of 1190 ± 60 nm) was synthesized by combining the sol-gel and the subsequent solvothermal treatment, and applied to CdS quantum-dot-sensitized solar cells (QDSSCs). This mesoporous spherical (MS) TiO 2 offers a high surface area (76.02 m 2 g −1 ), a high internal reflectance in the visible region and a pore accessibility. A conversion efficiency of 1.9% was achieved by CdS QDSSCs composed of the MS TiO 2 photoanode, which corresponds to ∼58% improvement as compared with the values obtained from the conventional devices made with 20-nm-sized nanocrystalline TiO 2 under AM 1.5 illumination of 100 mW cm −2 . Thus, the MS TiO 2 can be a promising candidate for the photoanode material of QDSSCs.
Journal of Materials Chemistry, 2009
In this paper we describe the preparation of CdTe quantum dot-sensitized solar cells (QDSSCs). We coated FTO substrates with 21 nm-diameter TiO 2 nanoparticles (NPs) and then immersed the system in poly(dimethyldiallylammonium chloride) (PDDA) solution under ambient conditions. The treated substrates were then subjected to 3 nm-diameter CdTe NP solution at 100 C for various periods of times. To increase the degree of deposition and to obtain CdTe QDs of various sizes, we performed the coating of the CdTe QDs through three heating cycles for 24, 12, or 6 h. The as-prepared (TiO 2 ) 3 -PDDA-(QD CdTe ) 3 -FTO electrodes were then used to fabricate (TiO 2 ) 3 -PDDA-(QD CdTe ) 3 -FTO QDSSCs employing 1-ethyl-3-methylimidazolium thiocyanate incorporating 1.0 M LiI and 0.1 M I 2 as electrolytes. The heating treatment allows the QDSSCs to harvest energy at a higher efficiency in the visible region of solar light. As a result, the as-prepared QDSSCs feature a high energy conversion efficiency (h ¼ 2.02%) and a high open-circuit photovoltage (V oc ¼ 850 mV) at 100% sunlight (AM1.5, 100 mW/cm 2 ). À redox couple. 20-22 RTILs such as 1-dodecyl-3-methylimidazolium iodide, 1-propyl-3-methylimidazolium iodide, and
Journal of Alloys and Compounds, 2014
Quicker and simpler chemical fabrication route is always desirable for synthesis of technologically important nanocrystals. Here we propose simple aqueous method for synthesis of type-II heterostructure of CdTe/CdSe core/shell nanocrystals without purification of CdTe seed at a relatively lower temperature of 80°C.Thesecore/shellnanocrystalsshowstructuralandopticalpropertiescomparabletothenanocrystalssynthesizedusingpurifiedCdTeseednanocrystals.LongerphotoluminescencelifetimewiththickershellsareobservedinsuchCdTe/CdSecore/shellheterostructuresgrownbybothprocedureswhichindicatesmorenon−radiativedecaychannelsarebeingaddedwithincreasingthicknessofshelllayer.Sensitizedsolarcellsarefabricatedusingthesegoodqualityunpurifiedcore/shellnanocrystals.Wefoundthatefficiencyofsolarcellisastrongfunctionofshellthicknessasthechargecarrierseparationisalsofunctionofshellthicknessinthesetype−IIheterostructurenanoparticles.Theincrementinshortcircuitcurrentdensityinnanocrystalshavingthickestshellis80°C. These core/shell nanocrystals show structural and optical properties comparable to the nanocrystals synthesized using purified CdTe seed nanocrystals. Longer photoluminescence lifetime with thicker shells are observed in such CdTe/CdSe core/shell heterostructures grown by both procedures which indicates more non-radiative decay channels are being added with increasing thickness of shell layer. Sensitized solar cells are fabricated using these good quality unpurified core/shell nanocrystals. We found that efficiency of solar cell is a strong function of shell thickness as the charge carrier separation is also function of shell thickness in these type-II heterostructure nanoparticles. The increment in short circuit current density in nanocrystals having thickest shell is 80°C.Thesecore/shellnanocrystalsshowstructuralandopticalpropertiescomparabletothenanocrystalssynthesizedusingpurifiedCdTeseednanocrystals.LongerphotoluminescencelifetimewiththickershellsareobservedinsuchCdTe/CdSecore/shellheterostructuresgrownbybothprocedureswhichindicatesmorenon−radiativedecaychannelsarebeingaddedwithincreasingthicknessofshelllayer.Sensitizedsolarcellsarefabricatedusingthesegoodqualityunpurifiedcore/shellnanocrystals.Wefoundthatefficiencyofsolarcellisastrongfunctionofshellthicknessasthechargecarrierseparationisalsofunctionofshellthicknessinthesetype−IIheterostructurenanoparticles.Theincrementinshortcircuitcurrentdensityinnanocrystalshavingthickestshellis300% compared to the core-shell nanocrystals having the thinnest shell prepared by us. We also found that sintering of photo-anode sensitized with these CdTe/CdSe nanocrystals is very important for achieving higher efficiency. Calculated maximum efficiency of the solar cell fabricated using core/shell nanocrystals with thickest CdSe shell is $2% with J SC = 8.9 mA/cm 2 and V OC = 0.53 V.
The photovoltaics of double-layered CdS/CdSe quantum dot (QD)-sensitizedsolar cells (QDSCs) were investigated. TheCdS/CdSe quantum dot was adsorbed on inverse opal (IO)-TiO 2. IO-TiO 2 electrodehas a honeycomb structure with largeinterconnected pores that lead to better infiltration despite thesmaller surface area than nanoparticulate electrode.Animprovement in the photovoltaic conversion efficiency (~ 3.8%) wasachieved compared with single-layered CdSe-QDSCs (~ 2.9%).We investigated the ultrafast photoexcited carrier dynamics (the electron and hole relaxation processes) ofCdS/CdSe-QDSCs byimproved-transient grating (TG) technique.TG technique basically depends on the refractive index changes duetophotoexcited carriers. The ultrafast carrier dynamics of CdS/CdSe-and CdSe-QDSCsshow fast (hole) and slow (electron) relaxation processes withdecay times of a fewpicoseconds and a few tens of picoseconds, respectively. The electron relaxation timewas shorter in theCdS/CdSe-QDSCs than in theCdSe-QDSCs, indicating a reduction in the numbers ofrecombination centers due to the pre-adsorbed CdS QDs layer.