Duy-Cuong Nguyen

3-D solar cells by electrochemical-deposited Se layer as extremely-thin absorber and hole conducting layer on nanocrystalline TiO2 electrode

A three-dimensional selenium solar cell with the structure of Au/Se/porous TiO2/compact TiO2/fluorine-doped tin oxide-coated glass plates was fabricated by an electrochemical deposition method of selenium, which can work for the extremely thin light absorber and the hole-conducting layer. The effect of experimental conditions, such as HCl and H2SeO3 in an electrochemical solution and TiO2 particle size of porous layers, was optimized. This kind of solar cell did not use any buffer layer between an n-type electrode (porous TiO2) and a p-type absorber layer (selenium). The crystallinity of the selenium after annealing at 200°C for 3 min in the air was significantly improved. The cells with a selenium layer deposited at concentrations of HCl = 11.5 mM and H2SeO3 = 20 mM showed the best performance, resulting in 1- to 2-nm thickness of the Se layer, short-circuit photocurrent density of 8.7 mA/cm2, open-circuit voltage of 0.65 V, fill factor of 0.53, and conversion efficiency of 3.0%.

The Effect of Annealing Temperature and KCN Etching on the Photovoltaic Properties of Cu(In,Ga)(S,Se)2 Solar Cells Using Nanoparticles

Cu(In,Ga)S2 nanoparticles were synthesized by a hot-injection method under a low-vacuum ambience, which were printed and annealed with Se vapor for Cu(In,Ga)(S,Se)2 solar cells. The Cu(In,Ga)S2 nanoparticles were around 14 nm, and the stable ink was obtained by dispersing the nanoparticles in hexanethiol. The crystallinity of the Cu(In,Ga)(S,Se)2 films increased with the increase in annealing temperature. Cu(In,Ga)(S,Se)2 solar cells with KCN etching after annealing showed better photovoltaic properties than KCN etching before annealing and without etching. The best cell was observed at an annealing temperature of C and KCN etching after annealing; the parameters of this cell were a short-circuit photocurrent density of 27.12 mA/cm2, open-circuit voltage of 0.42 V, fill factor of 0.38, and conversion efficiency of 4.3%.

Making nanoparticle ink for compound solar cells

Compound solar cells, such as those made from copper indium sulfide (CIS), copper indium gallium selenide (CIGS) and copper zinc tin sulfide/selenide (CZTS), are promising candidates for replacing silicon photovoltaic devices in the future. These types of cells have attractive properties including high efficiency (CIS:1 12.5%, CIGS:2 20.3%, CZTS:3 10.1%) and stability. Further, there are many more fabrication methods for compound cells than for silicon devices. They can be prepared both at low pressure (vacuum methods) and at atmospheric pressure (nonvacuum methods) using various techniques. Two examples are vacuum co-evaporation, where the thin films used in the cell are fabricated by the evaporation of precursor materials, and nonvacuum printing, where the absorber layers are printed on a substrate using a paste or ink—a solution of nanoparticles of a specific substance dispersed in a solvent. However, to date, compound solar cells that achieved high efficiency were mostly fabricated using vacuum methods, which drives up the cost of these devices. Non-vacuum fabrication methods are cheaper, with nonvacuum printing being a particularly promising technique since it is simple, fast, and can be used on a large scale. Our research focuses on fabricating printed CIS, CZTS and CIGS solar cells. The key aspect in producing these devices is synthesizing suitable ink. As the process for producing ink for all three types of devices is similar, here we describe only the synthesis of CIS ink. Our method to fabricate CIS nanoparticles is similar to that of Panthani and collaborators,4 but uses lower-cost materials. To synthesize CIS nanoparticles, researchers typically use sulfur powder as a sulfur precursor, and metal-organic (high cost) or inorganic materials (low cost) to produce copper and indium. In our work, we employed inorganic materials including copper (II) chloride dihydrate (CuCl2.2H2O) and indium chloride (InCl3), in addition to sulfur powder. Figure 1. Hot-injection synthesis of copper-indium-sulfide (CIS) nanoparticles.

Spray-Pyrolyzed Three-Dimensional CuInS2 Solar Cells on Nanocrystalline-Titania Electrodes with Chemical-Bath-Deposited Inx(OH)ySz Buffer Layers

Three-dimensional (3D) compound solar cells with the structure of have been fabricated by spray pyrolysis deposition of CuInS2 and chemical-bath deposition of Inx(OH)ySz for the light absorber and buffer layer, respectively. The effect of deposition and annealing conditions of Inx(OH)ySz on the photovoltaic properties of 3D CuInS2 solar cells was investigated. Inx(OH)ySz annealed in air ambient showed a better cell performance than those annealed in nitrogen ambient and without annealing. The improvement of the performance of cells with Inx(OH)ySz buffer layers annealed in air ambient is due to the increase in oxide concentration in the buffer layers [confirmed by X-ray photoelectron spectroscopy (XPS) measurement]. Among cells with Inx(OH)ySz buffer layers deposited for 1, 1.5, 1.75, and 2 h, that with Inx(OH)ySz deposited for 1.75 h showed the best cell performance. The best cell performance was observed for Inx(OH)ySz deposited for 1.75 h with annealing at 300 °C for 30 min in air ambient, and cell parameters were 22 mA cm-2 short-circuit photocurrent density, 0.41 V open-circuit voltage, 0.35 fill factor, and 3.2% conversion efficiency.

CuInS2 Superstrate Solar Cells with ZnO Compact Layer Fabricated by Totally Non-vacuum Methods

Abstract Solar cells with a superstrate structure of were fabricated with CuInS2 absorber, In2S3 buffer, and ZnO, deposited by spray pyrolysis. The ZnO films fabricated from zinc chloride and zinc acetylacetonate precursors had a rougher surface than film fabricated from the zinc acetate dihydrateprecursor. The band gap of the ZnO film on the FTO substrate was approximately 3.17 eV. The effects of annealing temperature and time on cell performance were analyzed. The cells with the ZnO layer annealed at 650 °C for 30 min showed the best photovoltaic properties. The parameters of the best cells were a short-circuit photocurrent density of 9.72 mA cm-2, open-circuit voltage of 0.55 V, fill factor of 0.45, and efficiency of 2.50%.

Superstrate CuInS 2 solar cells fabricated by spray-pyrolysis methods

CuInS<inf>2</inf> (CIS) films were deposited on In<inf>2</inf>S<inf>3</inf>/TiO<inf>2</inf>/FTO/glass under air by spray pyrolysis, resulting in superstrate-structured solar cells. We found the significant difference of images between SEM and optical microscope, which suggests crystallization of spray-pyrolysis CIS particles in In<inf>2</inf>S<inf>3</inf> layer. The In<inf>2</inf>S<inf>3</inf> covering layer was confirmed by Auger Electron spectroscopy. Titanium-doping in In<inf>2</inf>S<inf>3</inf> improved fill factor of CIS cells, however, the conversion efficiency was not changed. The best cells were achieved at 4 % sodium doping using 350 °C hot-plate and their cell parameters are open-circuit voltage = 0.551 V, photocurrent density = 11.65 mA/cm², fill factor = 0.45, and a conversion efficiency = 2.88%.