J. Kois

Terahertz radiation from nonstoichiometric CuInSe2 films excited by femtosecond laser pulses

We report on the observation of efficient terahertz radiation from the surface of CuInSe2 excited by femtosecond laser pulses. Terahertz radiation emitted by polycrystalline CuInSe2 layers manufactured by using electrodeposition technology was as powerful as the signals radiated by single-crystalline semiconductor surfaces. It has been found that terahertz radiation efficiency is critically dependent on the stoichiometry of the CuInSe2 layers. The results of a double-pulse excitation experiment have indicated that terahertz radiation from the photoexcited surfaces of CuInSe2 samples was caused by the presence of a built-in electrical field at those surfaces.

CuInS 2 /PEDOT Photovoltaic Structure

Structures based on combination of electrically conductive polymers with inorganic semiconductors are currently intensively investigated with the aim to prepare low-cost, largearea and flexible photovoltaic devices. In this study, multilayer structures consisting of CuInS 2 (CIS) and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonate (PSS) thin films were prepared and investigated for photovoltaic applications. Polycrystalline CIS absorber layers were synthesized on top of a layered structure on Cu tape substrate using socalled non-vacuum CISCuT technique. Thin PEDOT buffer layers doped with PSS were deposited onto KCN etched and vacuum annealed CIS films. The deposition was performed using the spin-casting technique from an aqueous dispersion of PEDOT/PSS mixed with Nmethylpyrrolidone, isopropanol, glycerin and epoxysilane additives. Optimal deposition parameters for stable PEDOT films with a good adherence to the surface of CIS were selected experimentally. The morphology and thickness of prepared films and structures was determined using SEM technique. Average film thickness was about of 1.5 μm for CIS and 50 nm for PEDOT films. Current-voltage and impedance characteristics were measured. Significant photovoltage and photocurrent of the photovoltaic structures were observed under standard illumination intensity. The best structure showed an open-circuit voltage of 510 mV and a shortcircuit current density of 20.2 mA/cm 2 .

Hybrid solar cells based on inorganic thin film structures and conjugated polymers

Hybrid solar cells based on a combination of conductive polymer poly (3,4-ethylenedioxyth1ophene) (PEDOT) doped with polystyrenesulfonate (PSS) and inorganic semiconductor CuIn(S,Se)2 (CISSe) were investigated. The CuInSe2 (CISe) absorber layers were electrodeposited on IT0 covered glasses from aqueous solutions with various ratios of elements. The ITO/In(O,S)/CISSe photovoltaic (PV) junctions were prepared by the sulfurization of ITO/CISe precursors at 450 °C in the H2S atmosphere. A PEDOT-PSS layer of p-type is considered as an alternative for the traditional window top layer on the CISSe absorber layer in the cell structure. The polymer deposition was performed using spin-casting technique. The PV properties of the prepared ITO/In(O,S)/CISSe and ITO/In(O,S)/CISSe/PEDOT- PSS structures were investigated, with special attention paid to the role of the conductive polymer layer in the cell structure.

Materials and technologies for photovoltaic applications from Estonia

In the Department of Materials Science of the Tallinn University of Technology, an EU project with the same title as the present communication is carried out. The aim of this paper is to summarize the results of the research and development of the different materials and polycrystalline solar cells obtained within the project. The topics addressed are: photoluminescence of different ternary compounds, thin films and thin film structures by different chemical methods, photovoltaic structures based on electrically conductive polymers and copper-indium-chalcogenide materials, monograin powders with a tailored composition and structure, and the technology of monograin layer solar cells.