The influence of the aluminium content on the photovoltaic performance of the p-Ga_1−xAl_xAs/p-GaAs/n-GaAs structure is investigated. An enhanced high-photon-energy spectral response is observed when the window layer has a direct gap. Also short-circuit currents and conversion efficiencies calculated in these devices indicate high values in the neighbourhood of those obtained with a high aluminium content. This is due to the high mobilities characterising direct valley electrons; i.e. the contribution of the window layer to the cell current is greatly enhanced, to the extent that the increased photogeneration in this layer does not lead to any significant loss.

Analytical expressions are proposed showing that the efficiency and fill factor of solar cells depend on the three normalised parameters r_m, r_L and g. These expressions are obtained with a new theoretical model, representing the metal-covered area of the solar cell.

The electrical performance of concentrated photovoltaic Si cells has been studied underthe application of real sunlight. The photogenerated current increases linearly with cell temperature at a rate of 5 mA/°C, and it increases with the normal incident solar intensity. The difference between the cell temperature and the lowest cooler temperature increases sharply with incident solar intensity. The module open-circuit voltage decreases with increasing cell temperature. The rate decreases with decreasing normal solar intensity. The module open-circuit voltage increases with normal incident solar intensity. The rate decreases as the incident solarintensity increases. The module efficiency decreases with increasing cell temperature at a ratewhich depends on incident solar intensity and cell temperature. As the incident solar intensity increases, the reduction in efficiency per degree rise in cell temperature decreases. For a given cell temperature, the module efficiency increases with incident power to a maximum and then decreases. A normalised empirical formula relating the incident solar intensity to the cell temperature, for the maximum efficiency condition, is obtained.

A new concept for treating the effects of dust on the electrical performance of photovoltaic concentrators is presented in the paper. The dust concentration in the atmospheric air around the concentrator is measured continuously during the test period. The rate of dust accumulation on the concentrator surface is determined. The concentrator performance degradation, as a result of dust accumulation, is related to the amount of dust accumulated per unit area of the collector surface (in g/m²) rather than the exposure time. It has been shown that major reductions in the short-circuit current and the efficiency are observed for dust accumulations up to 5.4 g/m². The accumulation of dust on the photovoltaic concentrator causes a successively larger ‘rounding’ of the I/V characteristic at constant incident direct normal radiation intensity and constant cell temperature. This effect is equivalent to an increase in the internal series resistance of the concentrator. This dust-equivalent series resistance increases with increasing dust accumulation.