M. Altosaar

Monograin layer solar cells

The paper presents results of studies directed towards the production of monograin powders of CuInSe for possible use in 2 solar cells preparation.The results concern the tailoring of chemical and defect composition of materials, development of the technology of manufacturing monograin layers (MGL) on the base of developed materials and the cleaning of open surfaces of the grains in the MGL by different mechanical, chemical and electrochemical methods.It is shown that up to now the low efficiency of MGL solar cells is associated with the chemical and defect composition of the monograin powder materials and with difficulties in cleaning the surfaces of the crystals in the MGL before depositing active contacts. 2003 Elsevier Science B.V. All rights reserved.

CuInSe2 Monograin Growth in CuSe-Se Liquid Phase

Isothermal growth of CuInSe2 monograin powders in molten CuSe-Se flux has been studied proceeding from Culn (1:1) alloy, Se and CuSe. The activation energy for linear crystal growth Ed = 0.28(±0.03) eV and the power of time dependence of crystal growth 1/n=0.27(±0.017) according to the equation: dm=At1/nexp (-Ed/kT) have been found. As a result homogeneous high-conductive (0.5 Ωcm) p-type CuInSe2 material (22.4 : 25.1 : 52.5) with single-crystalline grain structure and narrow-disperse granularity is synthesized from CuSe-Se solvent.

Cu2ZnSnSe4 Monograin Powders for Solar Cell Application

Cu₂ZnSnSe₄ monograin powders with different Zn/Sn concentration ratios were synthesized from binaries and elemental selenium, p-type CCu₂ZnSnSe₄ monograins of stannite structure had tetragonal shape with rounded edges. PL spectra showed one symmetrical band with peak position at 0.81 eV. Monograin layer solar cell structures graphite/Cu₂ZnSnSe₄/CdS/ZnO had open circuit voltage over 400 mV, short circuit current 15.5 mA/cm² and FF41 %

The nature of recombination centres in silver- and chlorine-doped CdS phosphors

Abstract The intensity of photoluminescence (PL) emission bands in CdS:Ag:Cl depends on the added Ag (10 16 −10 20 cm −3 ) and Cl (10 16 −10 19 cm −3 ) concentration and the partial pressure of Cd or S is measured. It is shown that the intensity of PL bands is a power function of the silver and chlorine concentration and the partial pressure of the components. The comparison between the experimental and theoretical curves permits one to determine the nature of the radiative and non-radiative recombination centres of Ag and Cl in CdS:Ag:Cl.

Chemical etching of Cu 2 ZnSn(S,Se) 4 monograin powder

Cu2ZnSn(S,Se)4 (CZTS,Se) monograin powders were synthesized in the liquid phase of molten KI as flux material from binary compounds in evacuated quartz ampoules. Monograin powders were subjected to various chemical treatments with several etchants (HCl, KCN, NH4OH and Br in methanol (Br2-MeOH)) to modify the crystal surface. Polarographic analyses of leaching solutions showed that Sn and Se were removed preferably by HCl etching. Treatment with 10% KCN dissolved mainly Cu, Sn and chalcogen, and ammonia solution removed selectively Cu and chalcogen in an approximate ratio of 1∶2. From XPS measurements we found that after etching with 1% Br2-MeOH the material surfaces were Sn-rich. The prepared monograin powders were used as absorber materials in monograin layer solar cells: ZnO/CdS/CZT(S,Se)/graphite. A combination of chemical treatments before the deposition of CdS led to the best parameters of Cu2ZnSn(S,Se)4 monograin layer solar cells. The here achieved efficiencies of solar cells were above 4%.

Powder materials and technologies for solar cells

The regularities of recrystallisation of initial powders of cadmium and zinc chalcogenides and chalcopyrites in different molten fluxes are studied. It is shown that the capillary phenomena in the solidliquid phase boundary, wetting of the solid phase with the liquid flux phase are the processes that determine the mechanism of recrystallisation. Results indicate to the possibility of manufacturing of powders of complicate semiconductor materials in monograin form and with qualities acceptable for Monograin Layer (MGL) design of solar cells. Influence of several technological processes to parameters of monograin powders and MGL solar cells are studied.

CZTS Monograin Powders and Thin Films

This paper reviews results of studies on different materials and technologies for polycrystalline solar cells conducted at Tallinn University of Technology. Structural properties and defect structure of kesterite CZTS compounds (Cu2ZnSnSe4, Cu2ZnSn(SSe)4) were studied. Influence of selenization parameters of a Zn-Cu-Sn stacked layer on the CZTS layer growth and on the morphology, distribution of elements was analyzed. All the results obtained have been used to optimize the technology of producing solar cell structures in different designs. Cu2ZnSnSe4 and, Cu2ZnSn(SSe)4 based monograin layer solar cells were developed.

Monograin A2B6 powders

This paper discusses the recrystallization mechanism, kinetics and morphology of the crystals of different A2B6 powders versus preparation conditions. It is shown that these parameters are mainly determined by the chemical nature and concentration of a flux.

SEM analysis and selenization of Cu-Zn-Sn sequential films produced by evaporation of metals

The formation of Cu2SnZnSe4 thin films in the selenization of different sequential metallic and alloy films is investigated. It is shown that the main process of low temperature selenization (up to 300degC) is the formation of different binary copper selenides on the layer surface. High temperature selenization (over 400degC) leads to the formation of Cu2ZnSnSe4 phase with some excess of a separate ZnSe phase. The content of ZnSe diminishes with the rise of the selenization temperature, but the selenized films stayed always multiphased. The size of the formed Cu2ZnSnSe4 crystals is controlled by the composition of the precursor.

Monograin layers and membranes for photovoltaics

The possibilities of producing monograin powders of different A2B6 and chalcopyrite materials; different technologies of manufacturing monograin layers and cleaning of open surfaces of grains in the monograin layer by mechanical, chemical and electrochemical methods were studied. It was shown that up to now too low efficiency of solar cells by the monograin layer is associated with the insufficient cleaning of surfaces of crystals in the monograin layer before depositing the active contacts.