Quantum Dots Co-sensitized Solar Cells Research Articles

Mixture deposition method for graphene quantum dots-based dye-sensitized solar cell

Unambiguously layer by layer (LBL) assembly of graphene quantum dots (GQDs), and dye (GQDs/dye) on TiO2 photoanode is the traditional and straightforward approach in the fabrication of graphene quantum dot-cosensitized solar cells (QDSSCs). Unfortunately, limited light absorption and low affinity of GQDs to TiO2 surface shadow the advantages of LBL and constrain its practical application. Herein, a new strategy of mixture configuration (GQDs+dye) was investigated. The experimental results demonstrated that the mixture of GQDs+N719 exhibited the highest efficiency of 3.01%. The increased Jsc (5.075 mA/cm2) and high charge collection efficiency (0.96) in the mixture sample indicated enhanced electron collection at TiO2. The less -OH groups on TiO2 provide a good surface intact of GQDs and N719, thus increasing the affinity between the photoanode and photosensitizers. In addition to that, the high surface potential (33.47 mV) of the premixed sample restricted the photogenerated electrons to go into a deep state, reducing back electron transfer. Therefore, mixture assembly of co-sensitization is an effective approach for light-harvesting in QDSSC.

MnS passivation layer for highly efficient ZnO–based quantum dot-sensitized solar cells

Interfacial engineering plays a very significant role in suppressing charge recombination and improving the photovoltaic performance in solar cells. The introduction of a buffer or passivation layer is an effective way to modify interfacial behaviours. In this paper, a new approach involving the deposition of a MnS passivation layer was studied to improve the photoelectric conversion efficiency (PCE) of CdS/CdSe quantum dot co-sensitized solar cells (QDSSCs). Compared to the pure CdS/CdSe co-sensitized solar cells, the introduction of the MnS passivation layer can not only modify the surface defects of the quantum dots and suppress charge recombination at the photoelectrode/electrolyte interface, but also enhance the light harvesting capability in terms of both the absorbance intensity and absorption range. This work may provide inspiration for future studies on the interfacial modification of QDSSCs. The best device performance with a ZnO photoanode could be achieved when the MnS passivation layer was deposited for 1 min for each of two successive ionic layer adsorption and reaction (SILAR) cycles. The PCE, open circuit voltage (Voc), short circuit current density (Jsc), and fill factor (FF) were 3.70%, 0.60 V, 13.74 mA cm−2, and 0.44, respectively.

ZnO/TiO2 core–shell heterojunction for CdS and PbS quantum dot-cosensitized solar cells

ZnO nanorods (NRs) with regular morphology were prepared through hydrothermal method, and the TiO2 shell was assembled onto the surface of ZnO NRs by spin coating to the ZnO/TiO2 core–shell heterojunction. CdS and PbS quantum dots (QDs) were used to cosensitize the ZnO/TiO2 nanostructure by direct adsorption (DA) and successive ionic layer adsorption and reaction, respectively. SEM, TEM, and HRTEM images show that the samples possessed a rough surface and four lattice fringes indicating the successful synthesis of the ZnO/TiO2/CdS/PbS composite structure. The ZnO/TiO2(10T)/CdS/PbS sample showed a high absorption intensity at a broad range of wavelength to visible light region. The ZnO/TiO2(10T)/CdS/PbS photoelectrode with QDSSCs showed the highest IPCE of 36.04% and photoelectric efficiency (η) of 1.59%; these values increased by approximately 550% and 150% compared with those of unsensitized ZnO (0.29%) and ZnO/TiO2(10T) (1.04%) and about 146% and 120% compared with those of ZnO/TiO2(10T)/CdS and ZnO/TiO2(10T)/PbS, respectively. The fill factor was 0.36, and the photocurrent density (Jsc) and open circuit voltage (Voc) reached the maximum values of 9.73 mA cm−2 and 0.46 V, respectively.

New Antimony Selenide/Nickel Oxide Photocathode Boosts the Efficiency of Graphene Quantum-Dot Co-Sensitized Solar Cells.

A novel assembly of a photocathode and a photoanode is investigated to explore their complementary effects in enhancing the photovoltaic performance of a quantum-dot solar cell (QDSC). While p-type nickel oxide (NiO) has been used previously, antimony selenide (Sb2Se3) has not been used in a QDSC, especially as a component of a counter electrode (CE) architecture that doubles as the photocathode. Here, near-infrared (NIR) light-absorbing Sb2Se3 nanoparticles (NPs) coated over electrodeposited NiO nanofibers on a carbon (C) fabric substrate was employed as the highly efficient photocathode. Quasi-spherical Sb2Se3 NPs, with a band gap of 1.13 eV, upon illumination, release photoexcited electrons in addition to other charge carriers at the CE to further enhance the reduction of the oxidized polysulfide. The p-type conducting behavior of Sb2Se3, coupled with a work function at 4.63 eV, also facilitates electron injection to polysulfide. The effect of graphene quantum dots (GQDs) as co-sensitizers as well as electron conduits is also investigated in which a TiO2/CdS/GQDs photoanode structure in combination with a C-fabric CE delivered a power-conversion efficiency (PCE) of 5.28%, which is a vast improvement over the 4.23% that is obtained by using a TiO2/CdS photoanode (without GQDs) with the same CE. GQDs, due to a superior conductance, impact efficiency more than Sb2Se3 NPs do. The best PCE of a TiO2/CdS/GQDs-nS2-/Sn2--Sb2Se3/NiO/C-fabric cell is 5.96% (0.11 cm2 area), which, when replicated on a smaller area of 0.06 cm2, is seen to increase dramatically to 7.19%. The cell is also tested for 6 h of continuous irradiance. The rationalization for the channelized photogenerated electron movement, which augments the cell performance, is furnished in detail in these studies.

Impacts of Reduced Graphene Oxide in CdS/CdSe Quantum Dots Co-sensitized Solar Cells

The introduction of various amounts of reduced graphene oxide (RGO) to CdS/CdSe quantum dots co-sensitized solar cells was investigated to enhance the light absorption and to promote the electron transfer. The characterization and comparison of optical and electrochemical properties as well as the performance of the resultant quantum dot-sensitized solar cells (QDSCs) with different amounts of RGO have been investigated systematically. The introduction of RGO demonstrated to enhance the light harvesting and consequently increase the short-circuit current density (Jsc). ZnS inserting between QDs and RGO can effectively block the charge recombination at the interface; however, the defects of RGO in the TiO2/QDs/ZnS/RGO photoanode still may accelerate the interface charge recombination in QDSCs and lead to a slight decrease of the open-circuit voltage (Voc). The balance between the light harvesting and charge recombination in RGO modified QDSCs is a key for achieving high power conversion efficiency (PCE). F...

Fabrication of ZnO/SnO2 hierarchical structures as the composite photoanodes for efficient CdS/CdSe co-sensitized solar cells

The composite photoanodes based on the ZnO/SnO2 hierarchical structures with high photoelectricity properties have been successfully synthesized, and used in the CdS and CdSe quantum dots co-sensitized solar cells (QDSSCs). In this experiment, the ZnO/SnO2 nanoparticles (ZS-NP) and hierarchical nanosheets-based microflowers (ZS-MF) were prepared by the one-step hydrothermal route and the morphologies of the products were controlled by the solvent variation. An improved power conversion efficiency of 4.98% was achieved for the cell based on the ZS-MF composite photoanodes, which showed an increase of 21.8% compared to the ZS-NP photoanodes (4.09%). This result is mainly connected to the unique superiority of the three-dimensional hierarchical microflower nanostructures for light scattering and quantum dots loading, which is responsible for the increase of photocurrent values and eventual PCE.

La Doping of CdS for Enhanced CdS/CdSe Quantum Dot Cosensitized Solar Cells

CdS/CdSe system of quantum dot cosensitized solar cells (QDCSCs) is one of the most attractive structures for high-efficiency due to its effect of level adjusting. However, the stepwise structure formed between levels of CdS and CdSe has a limitation for enhancing the efficiencies. Metal ions doping in quantum dots have emerged as a common way for changing the Fermi level, band gap, and conductance. Here we report an innovative concept for the rare earth materials La-doped of the CdS layer in the CdS/CdSe QDCSCs by means of the successive ionic layer adsorption and reaction (SILAR). Then we tested that La doped quantum dots can help more electrons accumulate in CdS film, which makes the Fermi level shift up and form a stepped structure. This method leads to enhanced absorption intensity, obviously increasing current density in CdS/CdSe QDCSCs. Our research is a new exploration for improving efficiencies of quantum dot sensitized solar cells.

Effect of CdS/Mg-Doped CdSe Cosensitized Photoanode on Quantum Dot Solar Cells

Quantum dots have emerged as a material platform for low-cost high-performance sensitized solar cells. And doping is an effective method to improve the performance of quantum dot sensitized solar cells (QDSSCs). Since Kwak et al. from South Korea proved the incorporation of Mg in the CdSe quantum dots (QDs) in 2007, the Mg-doped CdSe QDs have been thoroughly studied. Here we report a new attempt on CdS/Mg-doped CdSe quantum dot cosensitized solar cells (QDCSSC). We analyzed the performance of CdS/Mg-doped CdSe quantum dot cosensitized solar cells via discussing the different doping concentration of Mg and the different SILAR cycles of CdS. And we studied the mechanism of CdS/Mg-doped CdSe QDs in detail for the reason why the energy conversion efficiency had been promoted. It is a significant instruction on the development of Mg-doped CdSe quantum dot sensitized solar cells (QDSSCs).

Synthesis of hierarchical TiO2 flower-rod and application in CdSe/CdS co-sensitized solar cell

A hierarchical double-layered TiO2 flower-rod structure composed of three-dimensional (3D) TiO2 flowers and one-dimensional (1D) nanorods on transparent fluorine-doped tin oxide (FTO) conducting glass has been synthesized by a facile hydrothermal method. The possible formation mechanism of the hierarchical architecture is also proposed. When used in CdSe/CdS quantum dots co-sensitized solar cells (QDSSCs), the 1D ordered rutile nanorods at bottom can accelerate the electron transfer rate by providing direct electrical pathway for photogenerated electrons, while the 3D flowers formed on the top of nanorods can increase the adsorption of QDs due to the enlarged areas, and can also be used as a scattering layer. The performance of the CdSe/CdS/TiO2 flower-rod solar cell can achieve a short-circuit current density (Jsc) of 13.46 mA cm−2, and a open-circuit voltage (Voc) of 0.42 V, with a maximum power conversion efficiency of 2.31% under one sun illumination (AM 1.5 G, 100 mW cm−2), which is greatly higher than that of CdSe/CdS/TiO2 nanorod solar cell (1.63%).

Microsphere Light-Scattering Layer Assembled by ZnO Nanosheets for the Construction of High Efficiency (>5%) Quantum Dots Sensitized Solar Cells

This work reported on a bilayer photoelectrode constructed by ZnO nanoparticle (NP) film and ZnO microsphere (MS) scattering layer for CdS/CdSe quantum dot cosensitized solar cells (QDSCs) with a power conversion efficiency (PCE) of greater than 5%. We controlled the growth orientations of ZnO crystals to form nanosheets, which attached together and assembled into MS due to the high surface energy of the nanosheets. MSs were used as a top layer to effectively increase the light diffuse reflection and harvesting to enhance photogenerated current. In comparison with ZnO NPs photoelectrode, the short circuit current density (Jsc) of ZnO NPs/MSs photoelectrode increased from 10.3 mA/cm2 to 16.0 mA/cm2, which was an enhancement of 55%. To further increase the fill factor and PCE of QDSCs, ZnO NPs/MSs was treated in the solution of H3BO3 and (NH4)2TiF6 to form a barrier surface layer, which suppressed the charge recombination and prolonged electron lifetime. As a result, the solar cell displayed Jsc of 17.13 mA...

Anisotropic Nanostructure ZnO Photoelectrodes for CdS/CdSe Quantum Dot Sensitized Solar Cells

CdS/CdSe quantum dots co-sensitized solar cells (QDSCs) were prepared by combining the successive ion layer absorption and reaction (SILAR) method and chemical bath deposition (CBD) method for the fabrication of CdS and CdSe quantum dots, respectively. In this work, we designed anisotropic nanostructure ZnO photoelectrodes, such as nanorods/nanosheets and nanorods array, for CdS/CdSe quantum dots co-sensitized solar cells. Our study revealed that the performance of QDSCs could be improved by modifying surface of ZnO to increase the loading of quantum dots and reduce the charge recombination.

Constructing ZnO nanorod array photoelectrodes for highly efficient quantum dot sensitized solar cells

This work reports on a ZnO nanorod (NR) array photoelectrode for CdS/CdSe quantum dot cosensitized solar cells (QDSCs), which generated a high power conversion efficiency of 3.14%. ZnO NR arrays were fabricated by growing on a seeded indium-doped tin oxide (ITO) substrate without using a template or high temperature conditions. The ZnO NR served as the backbone for direct electron transport in view of its single crystallinity and high electron mobility. To improve the performance of the QDSC, we introduced a facile chemical surface modification of the ZnO NR array photoelectrodes. The chemical processing not only formed a barrier layer of TiO2 nanoparticles on the surface of the ZnO NR, which suppresses charge recombination by preventing the electrons in the ZnO conduction band from transferring to the oxidized ions in the electrolyte, but also modified the surface characteristics of the ZnO NR so as to harvest a greater amount of QDs and increase the short current density of the QDSC. As a result, the QDSC assembled with the modified ZnO NR array photoelectrode exhibited a high performance with Jsc, Voc, FF and η performance values equal to 9.93 mA cm−2, 0.61 V, 0.52 and 3.14%, respectively.

Effects of passivation treatment on performance of CdS/CdSe quantum-dot co-sensitized solar cells

Carrier recombination can greatly reduce the efficiencies of quantum-dot sensitized solar cells (QDSSCs). This work aims to find a general preparation route to reduce carrier recombination in QDSSCs. The effects of a series of passivation treatments on CdS/CdSe quantum-dot (QD) co-sensitized solar cells are investigated. The QDs were synthesized on a nanoporous TiO2 electrode by the successive ionic layer adsorption and reaction processes. The different types of treatment included a blocking layer, a fluoride-ion coating, a ZnS coating, annealing, a TiO2 scattering layer and an Au counterelectrode. The power conversion efficiency was observed to become three times larger after treatment. The effectiveness of each treatment method is as follows in descending order: blocking layer≅TiO2 scattering layer>Au counterelectrode>F− ions and ZnS coatings>annealing. The best cell yields a current density of 14.6mA/cm2 and a respectable power conversion efficiency of η=3.11% under AM 1.5 sun. The passivation procedure makes a useful general guide for researchers for the preparation of QDSSCs.

CdSe/CdS quantum dots co-sensitized TiO2 nanotube array photoelectrode for highly efficient solar cells

In this work, we designed and fabricated a novel one-dimensional CdSe/CdS@TiO2 core–shell nanotube array for quantum dots co-sensitized solar cells (QDSSCs) application. The three-component core–shell nanotube array structure was formed cascade by coating CdS nanoparticles with a successive ionic layer adsorption and reaction process and a thin CdSe layer by chemical bath deposition onto the vertical TiO2 nanotube arrays (TNAs), which enhanced the optical absorption in the visible region and presented an stepwise band-edge level structure to improve the charge separation. Under optimum conditions, the CdS/CdSe co-sensitized QDSSC demonstrated a power conversion efficiency (PCE) of 2.40% under 100mW/cm2 illumination of simulate sunlight. Furthermore, an improved QDSSC with a PCE up to 2.74% was obtained by sealed annealing of TNAs, due to the transformation of thin and smooth nanotube to thick and rough particle nanotube.