Influences of solvents on morphology,light absorbing ability and photovoltaic performance of Sb2S3-sensitized TiO2 photoanodes by chemical bath deposition method

Sb₂S₃-sensitized TiO₂ films were prepared with chemical bath deposition (CBD) method. The influences of acetone and acetic acid solvents on the morphologies of Sb₂S₃-sensitized TiO₂ films and their light absorbing ability were investigated. Furthermore, photoelectrochemical solar cells containing Sb₂S₃-sensitized TiO₂ photoanodes, polyaniline, and Pt counter electrodes were prepared to investigate the photovoltaic performance of these Sb₂S₃-sensitized TiO₂ films. It was found that the Sb₂S₃-sensitized TiO₂ photoanode prepared with CBD method in the solution containing acetic acid showed higher light absorption in short-wavelength region, lower charge transfer resistance and longer electron lifetime compared with that of the one prepared with CBD method in the solution containing acetone, resulting in better photovoltaic performance.     

Enhanced photovoltaic performance of quantum dot sensitized solar cells with Ag-doped TiO2 nanocrystalline thin films

Ag-doped titanium dioxide (TiO₂) nanocrystalline thin films have been prepared by the sol–gel dip coating method and used as photoanode to fabricate quantum dot sensitized solar cells. The X-ray diffraction studies reveal the formation of anatase phase without any impurity phase. The surface morphology studied using scanning electron microscope shows uniform distribution of particles. The optical band gap was found to be 3.5 and 3.4 eV for CdS quantum dot sensitized TiO₂ and CdS quantum dot sensitized Ag-doped TiO₂ thin film respectively. The Ag-doped TiO₂ based solar cell exhibited a power conversion efficiency of 1.48 % which is higher than that of TiO₂ (0.9 %).     

CuSbS2 thin films by heating Sb2S3/Cu layers for PV applications

In this work, we present the preparation of CuSbS₂ thin films of approximately 850 nm in thickness by heating glass/Sb₂S₃/Cu layers in low vacuum and their application in PV structures: Glass/SnO₂:F/n-CdS/p-CuSbS₂/C/Ag. The Sb₂S₃ thin films were chemically deposited from a solution containing SbCl₃ and Na₂S₂O₃ at 40 °C on well cleaned substrates. Copper thin films of 50 nm were thermally evaporated on Sb₂S₃ films of thickness ~600 and 800 nm and the glass/Sb₂S₃/Cu precursor layers were heated in vacuum at 300 and 350 °C for 1 h. Structural, morphological, optical and electrical characterizations of the annealed thin films were analyzed by X-ray diffraction, Atomic force microscopy, UV–Vis spectrometry and photoresponse measurements. Studies on identification and chemical state of the elements were done using X-ray photoelectron spectroscopy. Photovoltaic devices were prepared using CuSbS₂ thin films as absorber and chemical bath deposited CdS thin films as window layer on FTO coated glass substrates. The photovoltaic parameters of the devices were evaluated from the corresponding J–V curves, yielding J_sc, V_oc and FF values in the range of 1.03–1.55 mA/cm², 250–294 mV and 0.46–0.57 respectively, performed using a solar simulator under illumination of AM1.5 radiation.     

Moisture-preventing MAPbI3 solar cells with high photovoltaic performance via multiple ligand engineering

Perovskite solar cells present one of the most prominent photovoltaic technologies,yet their stability,and engineering at the molecular level remain challenging.We have demonstrated multifunctional molecules to improve the operating stability of perovskite solar cells while depicting a high-power conversion efficiency.The multifunctional molecule 4-[(trifluoromethyl)sulphanyl]-aniline(4TA)with trifluoromethyl(-CF₃)and aniline(-NH₂)moieties is meticulously designed to modulate the perovskite.The-CF₃ and-NH₂ functional groups have strong interaction with perovskite to suppress surface defects to improve device stability,as well as obtain large crystal grains through delaying crystallization.Moreover,this-CF₃ forms a hydrophobic barrier on the surface of the perovskite to prevent cell decomposition.Consequently,the performance of the perovskite solar cells is remarkably improved with the efficiency increased from 18.00% to 20.24%.The perovskite solar cells with multifunctional molecular maintaining 93% of their original efficiency for over 30 days(-55%humidity)in air without device encapsulation,exhibiting a high long-term stability.Moreover,the lead leakage issue of perovskite solar cells has also been suppressed by the built-in 4TA molecule,which is beneficial to environment-friendly application.Ultimately,we believe this multifunctional small molecule provides an available way to achieve high performance perovskite solar cells and the related design strategy is helpful to further develop more versatile materials for perovskite-based optoelectronic devices.     

Effect of atomic layer deposited ultra thin HfO2 and Al2O3 interfacial layers on the performance of dye sensitized solar cells

The objective of this work was to investigate the improvement in performance of dye sensitized solar cells (DSSCs) by depositing ultra thin metal oxides (hafnium oxide (HfO₂) and aluminum oxide (Al₂O₃)) on mesoporous TiO₂ photoelectrode using atomic layer deposition (ALD) method. Different thicknesses of HfO₂ and Al₂O₃ layers (5, 10 and 20 ALD cycles) were deposited on the mesoporous TiO₂ surface prior to dye loading process used for fabrication of DSSCs. It was observed that the ALD deposition of ultrathin oxides significantly improved the performance of DSSCs and that the improvement in the DSSC performance depends on the thickness of the deposited HfO₂ and Al₂O₃ films. Compared to a reference DSSC the incorporation of a HfO₂ layer resulted in 69% improvement (from 4.2 to 7.1%) in the efficiency of the cell and incorporation of Al₂O₃ (20 cycles) resulted in 19% improvement (from 4.2 to 5.0%) in the efficiency of the cell. These results suggest that ultrathin metal oxide layers affect the density and the distribution of interface states at the TiO₂/organic dye and TiO₂/liquid electrolyte interfaces and hence can be utilized to treat these interfaces in DSSCs.     

Enhanced photovoltaic performance of WO3 nanoparticles added dye sensitized solar cells

This study investigates the effect of various concentrations of Tungsten Oxide (WO₃) nanoparticles on the performance of dye sensitized solar cells. For that WO₃ nanoparticles are synthesized by using solvothermal method and annealed at room temperature, 100 and 400 °C. The crystalline and morphology of the synthesized WO₃ nanoparticles was characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Solar cell with 1 % WO₃ nanoparticles (annealed at 100 °C) added TiO₂ electrode exhibits an enhanced short-circuit current density of 12.94 mA cm^?2, open-circuit photo voltage of 0.67 V, fill factor of 0.57, and overall power conversion efficiency of 5.03 %.     

Enhancement of photovoltaic performance in dye-sensitized solar cells with the spin-coated TiO2 blocking layer

The TiO2 thin film layers were introduced with the spin-coating method between FTO electrode and TiO2 photoanode in dye sensitized solar cell (DSSC) to prevent electron back migration from the FTO electrode to electrolyte. The DSSC containg different thickness of TiO2 thin film (10-30, 40-60 and 120-150 nm) were prepared and photovoltaic performances were analysed with /-Vcurves and electrochemical impedance spectroscopy. The maximum cell performance was observed in DSSC with 10-30 nm of TiO2 thin film thickness (11.92 mA/cm2, 0.74 V, 64%, and 5.62%) to compare with that of pristine DSSC (11.09 mA/cm2, 0.65 V, 62%, and 4.43%). The variation of photoelectric conversion efficiency of the DSSCs with different TiO2 thin film thickness was discussed with the analysis of crystallographic and microstructural properties of TiO2 thin films.     

Advantages of transparent conducting oxide thin films with controlled permittivity for thin film photovoltaic solar cells

Our recent investigations have identified a pathway to produce transparent conducting oxide (TCO) films that demonstrate higher infrared transparency. The technique involves controlling the dielectric permittivity of the TCO film such that the electrical properties are maintained, but the plasma frequency (ω_p) is shifted to longer wavelength. This has the effect of reducing free-carrier absorption in the visible and near-infrared spectral region, thus producing a TCO film with higher optical transmission. The technique has been demonstrated for sputtered films of indium tin oxide by adding small amounts of ZrO₂ to a ceramic sputtering target, and for SnO₂:F films deposited by chemical vapor deposition using a metalorganic Zr source.     

The pyrolysis preparation of the compact and full-coverage AgSbS2 thin films and the photovoltaic performance of the corresponding solar cells

The preparation of the compact and full-coverage AgSbS2 thin films is firstly reported using the pyroly-sis of the Ag-butyldithiocarbamate and Sb-butyldithiocar...     

Reactive sputtering of thin Cu2S films for application in solar cells

Thin layers of cuprous sulphide were deposited by reactive r.f. sputtering; the target was pure copper and the sputtering gas was an ArH₂S mixture. We describe here how the composition of the films and their stoichiometry can be derived accurately both from X-ray diffraction and the optical reflection and transmission spectra. Measurement of the electrical resistivity can be used as a quick qualitative identification method.The application of these characterization methods to our sputtered films indicates that the crucial parameters to be controlled are the total pressure of the sputtering gas and, in particular, the partial pressure of the H₂S. Too low partial pressures of H₂S result in the presence of copper precipitations in the Cu₂S film, whereas too high H₂S partial pressures result in the presence of copper-deficient Cu_xS phases; there is an intermediate range of H₂S partial pressures in which pure chalcocite films (Cu₂S) are obtained. When these films were sputtered onto evaporated CdS layers, we obtained Cu₂S/CdS solar cells with a total area efficiency of above 4%.     

On the structure and transformation of the orange form of Sb2S3 layers

X-ray diffraction study showed that the mange modification of antimony trisulphide can neither be considered as amorphous material nor does it change into the black modification upon grinding. Thin vacuum-deposited layers, prepared by conventional thermal evaporation of the bulk material in 5 × 10^–6 torr on an amorphous substrate at room temperature, were crystalline. The behaviour of the electrical conductivity with temperature in the range 25 to 190° C indicated transition points at 80, 108, 135 and 175° C.     

Annealing and diffusion processes in thin film CdS/Cu2S solar cells

Diffusion of copper during post-fabrication annealing of CdS/Cu₂S thin film solar cells was studied by Auger electron spectroscopy. Depth profiles of the constituent element concentrations indicate that, for samples annealed in air, a deep penetration of copper into the cadmium sulphide layer occurs together with a significant out-diffusion of cadmium. In contrast, the copper penetration which results from vacuum or hydrogen annealing treatment is substantially less and no out-diffusion of cadmium is observed for annealing temperatures up to 400°C.     

Dependence of photovoltaic performance of solvothermally prepared CdS/CdTe solar cells on morphology and thickness of window and absorber layers

In the present work a new strategy for straightforward fabrication of CdS/CdTe solar cells, containing CdS nanowires and nanoparticles as a window layer and CdTe nanoparticles and microparticles as an absorber layer, are reported. CdS and CdTe nanostructures were synthesized by solvothermal method. X-ray diffraction analysis revealed that highly pure and crystallized CdS nanowires and nanoparticles with hexagonal structure and CdTe nanoparticles with cubic structure were obtained. Atomic force microscope and field emission scanning electron microscope images showed that CdS nanowires with length of several μm and average diameter of 35 nm, CdS nanoparticles with average particle size of 32 nm and CdTe nanoparticles with average particle size of 43 nm, were uniformly coated on the substrate by the homemade formulated pastes. Based on ultraviolet–visible absorption spectra, the band gap energies of CdS nanowires, CdS nanoparticles and CdTe nanoparticles were calculated 2.80, 2.65 and 1.64 eV, respectively. It was found that, the photovoltaic performance of the solar cells depends on thickness of CdTe and CdS films, reaching a maximum at a specific value of 6 μm and 225 nm, respectively. For such cell made of CdS nanowires and CdTe nanoparticles the V_OC, J_SC, fill factor and power conversion efficiency were calculated 0.62 V, 6.82 mA/cm², 59.7 and 2.53 %, respectively. Moreover, photovoltaic characteristics of the solar cells were dependent on CdTe and CdS morphologies. CdS/CdTe solar cell made of CdTe and CdS nanoparticles had the highest cell efficiency (i.e., 2.73 %) amongst all fabricated solar cells. The presented strategy would open up new concept for fabrication of low-cost CdS/CdTe solar cells due to employment of a simple chemical route rather than the vapor phase methods.     

Investigation of post-thermal annealing-induced enhancement in photovoltaic performance for squaraine-based organic solar cells

In this work, we have systematically investigated the post-thermal annealing-induced enhancement in photovoltaic performance of a 2,4-bis[4-(N, N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (DIBSQ)/C₆₀ planar heterojunction (PHJ) organic solar cells (OSCs). An increased power conversion efficiency (PCE) of 3.28% has been realized from a DIBSQ/C₆₀ device with thermal annealing at 100 °C for 4 min, which is about 33% enhancement compared with that of the as-cast device. The improvement of the device performance may be mainly ascribed to the crystallinity of the DIBSQ film with post-thermal annealing, which will change the DIBSQ donor and C₆₀ acceptor interface from PHJ to hybrid planar-mixed heterojunction. This new donor–acceptor heterojunction structure will significantly improve the charge separation and charge collection efficiency, as well as the open circuit voltage (V_oc) of the device, leading to an enhanced PCE. This work provides an effective strategy to improve the photovoltaic performance of SQ-based OSCs.     

Effect of highly ordered single-crystalline TiO2 nanowire length on the photovoltaic performance of dye-sensitized solar cells

One-dimensional semiconductor nanostructures grown directly onto transparent conducting oxide substrates with a high internal surface area are most desirable for high-efficiency dye-sensitized solar cells (DSSCs). Herein, we present a multicycle hydrothermal synthesis process to produce vertically aligned, single crystal rutile TiO(2) nanowires with different lengths between 1 and 8 μm for application as the working electrode in DSSCs. Optimum performance was obtained with a TiO(2) nanowire length of 2.0 μm, which may be ascribed to a smaller nanowire diameter with a high internal surface area and better optical transmittance with an increase in the incident light intensity on the N719 dye; as well as a firm connection at the FTO/TiO(2) nanowire interface.