Semiconductor-sensitized Solar Cells Research Articles

BiVO4 semiconductor sensitized solar cells

Semiconductor sensitized solar cells (SSSCs) are promising candidates for the third generation of cost-effective photovoltaic solar cells and it is important to develop a group of robust, environment friendly and visible-light-responsive semiconductor sensitizers. In this paper, we first synthesized bismuth vanadate (BiVO4) quantum dots by employing facile successive ionic layer adsorption and reaction (SILAR) deposition technique, which we then used as a sensitizer for solar energy conversion. The preliminary optimised oxide SSSC showed an efficiency of 0.36%, nearly 2 orders of magnitude enhancement compared with bare TiO2, due to the narrow bandgap absorption of BiVO4 quantum dots and intimate contact with the oxide substrate. This result not only demonstrates a simple method to prepare BiVO4 quantum dots based solar cell, but also provides important insights into the low bandgap oxide SSSCs.

Substrate placement angle-dependent growth of dandelion-like TiO2nanorods for solid-state semiconductor-sensitized solar cells

Hierarchical nanostructures grown directly on transparent conducting oxides hold the promise of overcoming the limitations of current semiconductor-sensitized solar cells based on random networks of nanoparticles. Here, we develop a facile substrate placement angle-dependent hydrothermal process to grow dandelion-like TiO2 nanostructures directly on transparent conductive oxides. TiO2 nanocrystals grown in solution during the synthesis process are found to promote the dandelion-like structure. By using these TiO2 nanostructures as photoanodes, Sb2S3 as the sensitizer, and P3HT as the hole-transporting material, we demonstrate fabrication of all-solid-state semiconductor-sensitized solar cells, which yield solar power conversion efficiency up to 4.71%. Electrochemical impedance spectroscopy indicates that moderate rod fusion at the base beneficially reduces electron recombination in the device. This work provides an innovative method for growing branched, one-dimensional TiO2 nanostructures that can be used for energy harvesting and storage.

High-quality SnO2@SnS2 core–shell heterojunctions: Designed construction, mechanism and photovoltaic applications

High-quality SnO2@SnS2 core–shell heterojunctions have been constructed through sulfurization of SnO2 nanoflowers self-sacrificial templates with H2S gas at relatively low temperature in this paper. The unreacted SnO2 core and the in-situ synthesized SnS2 shell are in good crystallinity with a low lattice mismatch interface. The formation mechanism of the core–shell heterostructures have been examined by experiments and theoretic computation from the perspectives of both adsorption and diffusion. When used as photoanode in all-solid-state semiconductor-sensitized solar cells, the SnO2@SnS2 core–shell heterojunctions based hybrid solar cell shows a promising conversion efficiency of 1.45% under 1 sun illumination, which is over 5 times than that of SnS2 quantum dot sensitized SnO2 electrode made by the common chemistry bath deposition method. The enhanced photovoltaic performance is contributed to the unique structure of SnO2@SnS2 core–shell heterojunctions which provide highly covered sensitizers and favored interface for suppressing the charge recombination from SnO2 to electrolyte. This strategy and understanding can be extended to other nanostructure core–shell architecture and fields.

Boron-doped MnTe semiconductor-sensitized ZnO solar cells

We studied the photovoltaic performance of boron-doped MnTe semiconductor-sensitized solar cells (B-doped MnTe SSCs). The B-doped MnTe semiconductor was grown on ZnO using two stages of the successive ionic layer adsorption and reaction (SILAR) technique. The two phases of B-doped semiconductor nanoparticles (NPs), i.e. MnTe and MnTe2 were observed with a diameter range of approximately 15–30 nm. The result of the energy conversion efficiency of the sample with boron doping was superior compared to that of an undoped sample, due to the substantial change in the short-circuit current density and the open-circuit voltage. In addition, plots of (αhv)2 vs hv with band gaps of 1.30 and 1.27 eV were determined for the undoped and B-doped MnTe NPs, respectively. It can be noted that the boron doping effects with the change in the band gap and lead to an improvement in the crystalline quality and also intimate contact between the larger sizes of MnTe NPs. Hence, a noticeably improved photovoltaic performance resulted. However, this kind of semiconductor sensitizer can be further extended by experiments on yielding a higher power conversion efficiency and greater stability of the device.

Ultra-small TiO2nanowire forests on transparent conducting oxide for solid-state semiconductor-sensitized solar cells

One-dimensional TiO2 nanostructures that have large specific surface area have broadened their applications in solar cells and water splitting, but their synthesis still remains a challenge. In this report, vertically ordered rutile TiO2 nanowires with an ultra-high coverage density of 2.4 × 1011 cm−2 and ultra-small width of barely ∼16 nm were synthesized on transparent conducting oxide by a facile solvothermal reaction using methanol and aqueous hydrochloride as solvent. The nanowires were fabricated with Sb2S3 into solid-state solar cells, which yielded a power conversion efficiency of 2.03%. Such a photoanode showed reduced electron recombination, due to moderate wire fusion at the bottom.

ChemInform Abstract: Surface Engineering of ZnO Nanostructures for Semiconductor‐Sensitized Solar Cells

AbstractReview: 277 refs.

Microstructure Control of Absorber Sb2S3 and p-Type Semiconductor CuSCN for Semiconductor-Sensitized Solar Cells (TiO2/Sb2S3/CuSCN)

Semiconductor-sensitized solar cells (SSSCs) were fabricated with a planar n-type TiO2 film, an antimony sulfide (Sb2S3) thin film as the absorber, and a transparent p-type CuSCN film. The deposition amount of Sb2S3 and the pn junction interface condition significantly affected the generation and recombination of photo carriers. Analysis of the microstructure and chemical state of the Sb2S3, and the microstructure of CuSCN films showed that the homogeneity of the Sb2S3 and CuSCN films, the oxidation of Sb2S3 and the CUSCN thickness determined the optimal amount of Sb2S3 and the highest photoelectric conversion efficiency. For the ETA solar cell with the highest photoelectric conversion efficiency (1.67%), Sb2S3 was deposited by sputtering (SP) and CuSCN by wiping (WI).

Microstructure Control of Absorber Sb2S3 and p-Type Semiconductor CuSCN for Semiconductor-Sensitized Solar Cells (TiO2/Sb2S3/CuSCN)

INTRODUCTION Semiconductor-sensitized solar cells (SSSCs) have greater stability of the semiconductor compared to organic dyes. Antimony sulfide (Sb2S3) is considered as a remarkable absorber for SSSCs due to its high absorption coefficient[1], low toxicity, abundance of its elements, and direct band gap with absorption in the visible range (approximately 1.8eV[2]). Sb2S3-based extremely thin absorber (ETA) solar cells reportedly have a 3.7% efficiency when the structure is porous TiO2 as n-type semiconductor and CuSCN as p-type semiconductor[3]. Photo-generated carriers are produced in Sb2S3 films, and a fast charge separation occurs due to the “thinness” of the absorber. However, the relation between the microstructure of absorber Sb2S3and the power generation characteristics of this type of ETA solar cells remains unclear.In this study, two deposition methods were introduced, namely, sputtering, which allows easy control of Sb2S3 deposition on thin TiO2 films by adjusting the deposition time, and inkjet-printing, which promises no physical contact with Sb2S3 when depositing CuSCN. Compared with Sb2S3 and CuSCN’s previous deposition methods, chemical bath deposition (CBD) and wiping, new deposition methods have their advantages. Improved cell efficiency is expected by controlling the microstructure of absorber Sb2S3and p-type semiconductor CuSCN with these two deposition methods. EXPERIMENTAL A thin TiO2 film was deposited on transparent conductive oxide (TCO) glass by spray pyrolysis. Sb2S3 was then deposited on this film by CBD from a solution of SbCl3 and Na2S2O3 (Aldrich). Alternatively, Sb2S3 film was deposited by sputtering using a Sb2S3 target of 99.9% purity (Kojundo Chemical) in an argon atmosphere with a base pressure of 5×10−4 Pa and with a launch power of 50 W. Both of these amorphous Sb2S3 films deposited by CBD and sputtering were then annealed in nitrogen at 320°C for 20 min to yield dark-brown crystalline stibnite. CuSCN was deposited by wiping or by inkjet-printing in an ambient atmosphere using a slightly under-saturated solution of CuSCN in dipropyl sulfide heated to 80°C. ETA solar cells were completed by depositing a gold film as the electrode by vacuum evaporation. I-V curves were measured using a solar simulator (CEP-25MLH) under simulated AM1.5, 100mW/cm2 sunlight and in the dark. Photovoltaic parameters, i.e. short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and cell efficiency (η) were determined from the I-V curves. For the field emission scanning electron microscopy (FE-SEM) images, samples were prepared with a cross-section polisher (CP) and by deposition of a platinum coating. RESULTS AND DISCUSSION Figure 1 shows the dependence of Jsc of ETA solar cells upon absorbance of sputter-deposited Sb2S3 at 500 nm. Absorbance depends on the thickness of Sb2S3. By controlling the deposition time of Sb2S3, the film thickness can easily be controlled by sputtering. Sb2S3 absorbance around 0.6 yielded the highest Jsc. With thinner films, the number of absorbed photons is not sufficient to yield a high amount of photo-generated carriers, whereas thicker films increase the amount of recombination of photo-generated carriers. Cell efficiency of ETA solar cells with sputter-deposited Sb2S3 is clearly improved compared with CBD-deposited Sb2S3(Table 1).Figure 2 compares cross-sectional FE-SEM images of typical cells with wiping-deposited and inkjet-printed CuSCN films. The inkjet-printed CuSCN film exhibited large holes and was approximately two times thicker than the wiping-deposited CuSCN film. Table 2 shows the photovoltaic parameters of ETA solar cells with wiping-deposited and inkjet-printed CuSCN films. In this study, ETA solar cells with wiping-deposited CuSCN films exhibited better power generation characteristic compared with inkjet-printed CuSCN films. However, the deposition conditions for inkjet-printing still need optimization, and cell efficiency is expected to improve for this method. CONCLUSION In summary, with the new deposition methods introduced in this study, namely sputtering and inkjet-printing, absorber Sb2S3 and p-type semiconductor CuSCN were deposited successfully. By controlling the microstructure of Sb2S3, ETA solar cell efficiency was improved. The inkjet-printing conditions still need optimization to yield a higher cell efficiency. REFERENCE [1] Versavel et al. ,Thin Solid Films, 515,7171-7176(2007)[2]Mane et al.,Master.Chem.Phys,141,2871-2877(1994)[3]S.Nezu et al., J.Phys.Chem.C, 114, 6854-6859(2010)

Solar Cells: Triple-Yolked ZnO/CdS Hollow Spheres for Semiconductor-Sensitized Solar Cells (Part. Part. Syst. Charact. 7/2014)

Solar Cells: Triple-Yolked ZnO/CdS Hollow Spheres for Semiconductor-Sensitized Solar Cells (Part. Part. Syst. Charact. 7/2014)

Surface engineering of ZnO nanostructures for semiconductor-sensitized solar cells.

Semiconductor-sensitized solar cells (SSCs) are emerging as promising devices for achieving efficient and low-cost solar-energy conversion. The recent progress in the development of ZnO-nanostructure-based SSCs is reviewed here, and the key issues for their efficiency improvement, such as enhancing light harvesting and increasing carrier generation, separation, and collection, are highlighted from aspects of surface-engineering techniques. The impact of other factors such as electrolyte and counter electrodes on the photovoltaic performance is also addressed. The current challenges and perspectives for the further advance of ZnO-based SSCs are discussed.

All-Solid Semiconductor-Sensitized Solar Cells Made by Electrodeposition

It would be very attractive to fabricate (Extremely Thin Absorber) ETA-solar cells using one single technique of deposition such as the electrochemical one, as this would facilitate the assembly of the solar cells and reduce cost of production. In the ZnO-NWs/CdSe/CuSCN solar cells, the ZnO nanowires (NWs) and the absorber, CdSe, were already made by electrochemical deposition. In this paper, the electrodeposition of the 2D ZnO buffer layer and p-type CuSCN was investigated as well as the possibility to use them in the solar cell assembly. Formation of vertically free standing CuSCN nanowires opened the route to built ETA-solar cells with an inverted configuration.

Higher Open Circuit Voltage and Reduced UV-Induced Reverse Current in ZnO-Based Solar Cells by a Chemically Modified Blocking Layer

Solid-state semiconductor-sensitized solar cells require a thin, dense hole-blocking layer at the conducting glass substrate (F-doped tin oxide (FTO)) to prevent shorting beween the FTO and hole conductor. We found that by adding a small amount of Sb ions to a ZnO chemical deposition bath a thin (few tens of nanometers thick) dense and uniform layer of Sb-incorporated ZnO forms. Here we investigate the electronic properties of this layer in comparison to the continuous ZnO layer at the base of the ZnO rods formed in the standard preparation. Devices incorporating the Sb-incorporated dense layer followed by a standard ZnO nanorod growth, onto which CdS or CdSe was grown followed by a CuSCN hole conductor, showed 100–200 mV higher photovoltage together with occasional improvement in the short-circuit current. Electrochemical and electrical measurements indicated complete coverage of the FTO substrate by both preparations; however, the shunt resistance (resistance to a reverse leakage current) in the cells (and films) made using the Sb-incorporated ZnO layer is dramatically increased. Using bias-dependent incident photon-to-electron conversion efficiency studies, we found that an increased dark or leakage current develops in the cell on illumination with UV light together with application of a forward bias. This can be explained by the presence of a “Schottky junction” at the FTO\ZnO interface. This increased leakage current is significantly larger in cells without the Sb-incorporated ZnO compact layer.

Triple-Yolked ZnO/CdS Hollow Spheres for Semiconductor-Sensitized Solar Cells

A new kind of complex hollow structure, ZnO/CdS triple-yolked hollow spheres (TYs), is prepared using a facile method. The formation mechanism is described in terms of a combined effect of the bubble-assisted Ostwald ripening and appropriate ion-exchange processes. The structural effect of ZnO hollow microspheres on the energy conversion efficiency is investigated. The uniqueness of TYs morphology leads to a 37% enhancement in energy conversion efficiency for SSSCs, as compared with single-shelled hollow spheres. The method using controlled ZnO/CdS yolk-in-shell structures in SSSCs presents obvious advantages in the generation of light scattering and makes full use of the internal structures of the photoelectrode. It also provides a feasible synthetic approach for fabrication of other complex hollow structures made of multicomponent functional heteromaterials.

Bandgap-graded ZnO/(CdS)1−x(ZnS)x coaxial nanowire arrays for semiconductor-sensitized solar cells

Bandgap-graded ZnO/(CdS)1−x(ZnS)x (0 ≦̸ x ≦̸ 1) coaxial nanowire arrays on transparent conducting oxide substrates have been successfully fabricated by a facile two-step-approach, combining hydrothermal method and successive ion exchange reactions. Energy-dispersive x-ray spectroscopy elemental analysis suggests that the shells are composed of (CdS)1−x(ZnS)x double-layer structures, which are thoroughly and tightly synthesized on the ZnO cores, and play the role of sensitizers. The as-prepared ZnO/(CdS)1−x(ZnS)x coaxial nanowire arrays are demonstrated to be controllably adjusted in their optical absorption from ultraviolet to green via compositional effect, and are promising electrodes for semiconductor-sensitized solar cells. The photoelectrode based on the ZnO/CdS coaxial nanowire array shows good performance with power conversion efficiency of 2.093%, a short-circuit current density 7.733 mA cm−2, and an open-circuit voltage 0.536 V.

Sb2Se3 Liquid-Junction Semiconductor-Sensitized Solar Cells

We report on the photovoltaic performance of liquid-junction Sb2Se3 semiconductor-sensitized solar cells (SSCs), prepared by growth of Sb2Se3 nanoparticles on a nanoporous TiO2 electrode using the solvothermal method. The growth of nanoparticles was investigated as a function of reaction time and solution concentration. The optimal sample was obtained by reacting a 0.1 M antimony solution with a 0.09 M selenium solution for 16 h. The best cell yielded an open-circuit voltage of 0.51 V, a short-circuit current density of 4.14 mA/cm2, a fill factor of 55% and an efficiency of 1.08% under 100 mW/cm2 illumination. A potential advantage is that the Sb2Se3 SSCs are stable in the polyiodide electrolyte. The optical absorption spectra suggest that, with improving sample growth, Sb2Se3 solar cells could achieve efficiencies significantly higher than the present value.

Enhanced Photovoltaic Performance in AgSbS2 Liquid-Junction Semiconductor-Sensitized Solar Cells

Ternary semiconductor AgSbS2 nanoparticles have been demonstrated to be a potential absorber material for solar cells. This work reports on the improved photovoltaic performance of liquid-junction AgSbS2 semiconductor-sensitized solar cells, prepared by growth of AgSbS2 nanoparticles on a nanoporous TiO2 electrode using the successive ionic layer adsorption and reaction process. The dependence of performance on the counter electrode and annealing atmosphere was investigated. The optimal performance was found in solar cells annealed in a N2 atmosphere with Au or Cu2S counter electrode. The best cell yielded a short-circuit current density Jsc of 8.30 mA/cm2, a open-circuit voltage Voc of 0.30 V, a fill factor of 32.8% and an efficiency η of 0.79% under 100 mW/cm2 light illumination. As the light intensity was reduced to 0.148 sun, the η increased to 1.28%, which is ∼ 300% larger than the η of 0.42% reported previously.

Lead Antimony Sulfide Semiconductor-Sensitized Solar Cells

We present a new, rare in nature, ternary semiconductor sensitizer, Pb5Sb8S17, for solar cells. Pb5Sb8S17 nanoparticles were synthesized on nanoporous TiO2 electrodes using a two-stage successive ionic layer adsorption and reaction process. Post-deposition annealing transformed the two-stage film into the Pb5Sb8S17 phase. The Pb5Sb8S17-coated TiO2 electrodes were assembled into liquid-junction semiconductor-sensitized solar cells. The best cell yielded a short-circuit current density of 11.04mA/cm2, an open-circuit voltage of 0.45V, a fill factor of 39.1% and a power conversion efficiency η of 1.94% under AM 1.5, 100 mW/cm2 light illumination. The external quantum efficiency (EQE) spectrum covered the spectral range of 350–750nm with a maximal EQE of ∼54% at λ=575nm. At a reduced light intensity of 0.118 sun, the η increased to 2.51%, a respectable value for a new sensitizer.

Tailoring of boron-doped MnTe semiconductor-sensitized TiO2 photoelectrodes as near-infrared solar cell devices

We studied the photovoltaic performance of a new tailoring of boron-doped MnTe semiconductor-sensitized solar cells (B-doped MnTe SSCs). The B-doped MnTe semiconductor was grown on TiO2 using two-stages of the successive ionic layer adsorption and reaction (SILAR) technique as a photoelectrode. The phase of the boron-doped MnTe and MnTe2 semiconductor as sensitizers were characterized with ∼20–50nm in diameter. The B-doped MnTe(5) exhibited the best efficiency of 0.04%, compared to that of the undoped sample of 0.006%. In addition, the band gaps of 1.30 and 1.26eV were determined for the undoped and B-doped MnTe NPs, respectively. The change in the band gap after boron doping was performed due to crystal quality improvement and the larger size of the MnTe NPs, leading to a broader absorption of the sensitizer and a noticeable improvement in the photovoltaic performance. This kind of semiconductor and synthesis procedure can be applied for further improvement in a higher efficiency and more stability in SSCs.

Enhanced Photovoltaic Performance of Semiconductor-Sensitized ZnO–CdS Coupled with Graphene Oxide as a Novel Photoactive Material

We report, for the first time, a ternary hybrid composite of ZnO, CdS, and graphene oxide (GO) as a one-coat paintable solution in performing the role of a photoanode for the semiconductor-sensitized solar cell, wherein hierarchical ZnO-CdS heteroarrays are embedded onto the GO sheets. The photoconversion properties of the hybrid ternary-system-based photoanodes are evaluated in the photovoltaic devices having Pt and Ag as the counter electrodes with sulfide/polysulfide redox couple as the electrolyte. Power conversion efficiency (PCE) of ~2.82% has been achieved with a short-circuit current density (Jsc) of ~7.3 mA/cm(2), a maximum open-circuit voltage (Voc) of 703 mV, and a fill factor (FF) of 54% for the photovoltaic cell with Pt as a counter electrode. The identical hybrid photoanode against the Ag counter electrode resulted in the following values: PCE ≈ 1.96%, Jsc ≈ 5.7 mA/cm(2), Voc ≈ 565 mV, and 63% FF. The band position proximity of CdS, ZnO, and GO in the proposed ternary system facilitates an efficient electronic interactions thereby promoting the electron transport within CdS-ZnO-GO. The hierarchically grown CdS nanorods over ZnO nanoparticle act as the sensitizer for ZnO, enhancing the visible light harvesting ability. The loading of 1.0 wt% of GO to ZnO-CdS results in enhanced separation of photogenerated electrons and holes within the photoactive layer, thereby improving the photovoltaic performance. The electronic interactions of GO to ZnO-CdS is evident from the drastic quenching of fluorescence, reduced exciton lifetime and Raman scattering measurements. In order to study the effect of GO in the photovoltaic performance, we have compared our result with the photoelectrical parameters of the devices fabricated using the binary ZnO-CdS composite as GO-free photoanodes.

All-Solid Semiconductor-Sensitized Solar Cells Made By Electrodeposition

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