Sanjay Kumar Swami

Reduced ultraviolet light induced degradation and enhanced light harvesting using YVO4:Eu3+ down-shifting nano-phosphor layer in organometal halide perovskite solar cells

We report a simple method to mitigate ultra-violet (UV) degradation in TiO2 based perovskite solar cells (PSC) using a transparent luminescent down-shifting (DS) YVO4:Eu3+ nano-phosphor layer. The PSC coated with DS phosphor showed an improvement in stability under prolonged illumination retaining more than 50% of its initial efficiency, whereas PSC without the phosphor layer degraded to ∼35% of its initial value. The phosphor layer also provided ∼8.5% enhancement in photocurrent due to DS of incident UV photons into additional red photons. YVO4:Eu3+ layer thus served a bi-functional role in PSC by reducing photo-degradation as well as enhancing energy conversion efficiency.

Spray deposited copper zinc tin sulphide (Cu2ZnSnS4) film as a counter electrode in dye sensitized solar cells.

Stoichiometric thin films of Cu2ZnSnS4 (CZTS) were deposited by the spray technique on a FTO coated glass substrate, with post-annealing in a H2S environment to improve the film properties. CZTS films were used as a counter electrode (CE) in Dye-Sensitized Solar Cells (DSCs) with N719 dye and an iodine electrolyte. The DSC of 0.25 cm(2) area using a CE of CZTS film annealed in a H2S environment under AM 1.5G illumination (100 mW cm(-2)) exhibited a short circuit current density (JSC) = 18.63 mA cm(-2), an open circuit voltage (VOC) = 0.65 V and a fill factor (FF) = 0.53, resulting in an overall power conversion efficiency (PCE) = 6.4%. While the DSC using as deposited CZTS film as a CE showed the PCE = 3.7% with JSC = 13.38 mA cm(-2), VOC = 0.57 V and FF = 0.48. Thus, the spray deposited CZTS films can play an important role as a CE in the large area DSC fabrication.

Effect of electric field on the spray deposited poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate) layer and its use in organic solar cell

Spray process under different applied voltages (0 V to 700 V) is used for the deposition of poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) hole transport layer (HTL). The deposition of PEDOT:PSS film by spray process under the effect of electric field results in smoother film morphology, increase in conductivity and reduction in the sheet resistance. The improvement in surface morphology and conductivity enhancement of PEDOT: PSS films are the key to the improvement in the J–V characteristics of ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell structures. The XPS peak height for PEDOT at 164.4 eV increased by 47% and that for PSS at 169.0 eV decreased by 30%, showing that the enhancement in the conductivity of the films deposited under electric field is due to the change in the PEDOT: PSS ratio. The organic solar cell using the electric field (created using 700 V) assisted spray deposited PEDOT:PSS film exhibit 42% and 69% improvement in the short circuit current density(Jsc) and power conve...

Eu3+ doped down shifting TiO2 layer for efficient dye-sensitized solar cells

Europium doped TiO2 (TiO2:Eu3+) down-shifting (DS) nanophosphors (NPrs) were synthesized by the solution-combustion method with different concentrations of Eu3+. The X-ray diffraction results confirmed the formation of a polycrystalline tetragonal structure of the TiO2. The emission of colour of the TiO2:Eu3+ DS NPr was tuned by varying the doping concentration of Eu3+. The photoluminescence results confirmed that the TiO2:Eu3+ DS NPrs converted the UV light into visible light by energy down-conversion process, i.e. down-shifting of high energy UV photons to low energy visible photons. These TiO2:Eu3+ DS NPrs were used to enhance the efficiency of the Dye sensitized solar cell from 8.32% to 8.80%.

Effect of electric field on spray deposited zinc sulphide films

Zinc sulphide (ZnS) thin films were deposited on soda lime glass substrate using spray technique with a DC voltage (300 V) applied to the nozzle to create an electric field during the spray deposition. Spray deposition of ZnS film under an electric field, resulted in change of the surface morphology, transmission, and enhancement in crystallinity of the film. The band gap of the spray deposited ZnS film was found to be 3.62 eV. Transparent ZnS film with the benefit of large area and low cost spray technique can be suitable for solar cell window layer application.

Structural and electrical properties of electric field assisted spray deposited pea structured ZnO film

Spray deposition of ZnO film was carried out. The uneven growth of ZnO nanostructures is resulted for spray deposited ZnO film. Application of DC voltage (1000V) during spray deposition provides formation of pea like structures with uniform coverage over the substrate. Electric field assisted spray deposition provides increased crystallinity with reduced resistivity and improved mobility of the ZnO film as compared to spray deposited ZnO film without electric field. This with large area deposition makes the process more efficient than other techniques.

Effect of sulphurisation on the activation energy of spray deposited kesterite (Cu2ZnSnS4) films

Spray deposited kesterite (Cu2ZnSnS4) thin films were annealed in a controlled sulphur environment at 500˚C for one hour. Temperature dependence measurement of the electrical conductivity indicated two types of conduction are present: (i) at low temperatures due to nearest neighbor hooping (NNH) and (ii) at high temperatures due to hole excitation into the conduction. The as deposited films showed both the conduction mechanisms, but on annealing the CZTS film, the conduction takes place only due to hole excitation into the conduction band. The absence of NNH conduction is indicative of the effect of annealing in removing the defect levels which can be important for improving the device performance.

Improvement in the performance of inverted organic solar cell using electric field assisted spray deposited ZnO layer

ZnO film was deposited using spray technique. The application of electric field (applying a DC voltage = 700V to the nozzle) during spray deposition provide compact nanostructured film of ZnO as compared to agglomerated ZnO film deposited using spray process. The ZnO film deposited after applying DC voltage during spray process showed good crystallinity as well as transmittance in the visible range. Use of this crystalline, compact layer of ZnO in inverted organic solar cell (ITO/ZnO/P3HT: PCBM/Ag) provide improved efficiency of 2.8% with JSC of 14.0 mA/cm2, VOC of 0.55V and FF of 36%. Thus the process remove the need of any post deposition treatment to improve the film quality as well as solar cell performance.