A. Jagomägi

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.

Photoluminescence studies of heavily doped CuInTe2 crystals

The photoluminescence spectra of heavily doped CuInTe2 and their dependence on the temperature and excitation power were measured. At 10 K an asymmetric broad peak at 0.98 eV was observed. The PL peak position did not depend on the excitation power, but had a characteristic dependence on the sample temperature. Our computer simulations proved that this behaviour is in good compliance with the Shklovskij/Efros model of heavily doped semiconductors with spatially varying potential fluctuations. Therefore, the PL band was attributed to the band-toimpurity type recombination and the corresponding level to the single acceptor at 70 meV, which is most probably caused by copper vacancy.

Device characteristics of CuInSe2-based solar cells

Ternary chalcopyrite semiconductor CuInSe2 (CIS) is a promising material for the fabrication of high-efficiency low-cost solar cells. However, various recombination losses decrease the efficiency of the cells and deteriorate their other characteristics. To identify the recombination channels and to obtain information about the related defects, we conducted current-voltage measurements at various temperatures, followed by admittance spectroscopy measurements and bias dependent quantum efficiency measurements. Two types of solar cells were studied: the ones based on the CIS monograin layers, and the others based on CuInGaSe2 thin films. The temperature dependence of the open-circuit voltage of the monograin cells demonstrated that the dominant recombination channel involves CIS-CdS interface states. According to the admittance spectroscopy data, the states lie at 150-166 meV below the conduction band of CIS. In some samples, a defect state at about 45 meV was observed. The quantum efficiency measurements revealed the influence of the sulphur post-treatment on the band gap of the absorber material. The derivative curves brought out the influence in the best possible way.

Effects of PV microgeneration on rural LV network voltage quality

Increase in photovoltaic (PV) systems integrated into low-voltage (LV) distribution networks has created a pressing need for analysis of the effects of these systems on power quality and supply reliability. The main aim of this study was to analyze the effects of small-scale PV-system power generation on voltage quality in a rural LV distribution network. In the analysis based on real field measurements, the numerical and graphical methods of data analysis were used. Thus, correlations between PV-system power (P(pv)) generation and voltage quality parameters in the LV-grid were examined.