In contrast to the successful application of analytic equations to the current-voltage behaviour of crystalline silicon solar cells in the dark and under AM1.5 illumination, the description of a-Si:H solar cells parameters requires device modelling concepts taking the full set of semiconductor equations into account. This in particular holds for the explanation of the temperature dependence (225-400K) of experimentally determined a-Si:H p-i-n solar cell parameters. Device modelling calculations show that the observed decrease of the short circuit current at AM1.5 with lower T is much more effected by the additional charge trapped in the tail states and recharging of defect states than by the broadening of the gap. The induced electric field distortion blocks the extraction of photo generated holes. The open circuit voltage V-oc increases with lower T which is caused by the same trapping effect.

An experimental and numerical study of a-SiGe:H based solar cells with band gap graded i-layer in the shape of a ‘V’ is presented. The variation of the location of the band gap minimum has strong influence on the solar cell performance. Comparisons of experimental and simulated data of the dark IV-behavior, IV-curves under illumination and the quantum efficiency allow insights into the transport and recombination behavior within the solar cell. The simulations reveal that the position as well as the charge state of the defects determine the device characteristics.

VHF-PECVD at 110 MHz was used to deposit micro-crystalline p-layers on glass substrates for detailed analysis and onto ZnO coated substrates for incorporation into p-i-n solar cell structures. Solar cell and film analysis confirmed that the films incorporated into the solar cells contained significant crystalline silicon volume fractions despite being only 30 nm thick. The p-i-n solar cells employing a micro-crystalline silicon p-layer deposited on ZnO coated substrates had series resistances, fill factors and V-OC similar to those of the reference solar cells deposited onto SnO2 coated substrates and having optimized amorphous silicon-carbon p-layers. The short circuit current of the micro-crystalline p-layer case was 10 percent lower than that of the reference cell indicating that further optimization is required.

Transient photocurrent response measurements have been used to characterize deep level impurities in amorphous silicon solar cells. These measurements are based on the analysis of the current deficiency and the overshoot in the photocurrent transients of a solar cell at the onset of an irradiation pulse as a function of the preceding dark time interval. The current deficiency is a measure for the carriers emitted from traps during the preceding dark time. Variation of temperature changes the reemission probability from traps, a decrease of irradiation wavelength reduces the generation depth of photocarriers within the i layer, electric bias voltage changes the electric field in the i layer. Thus the influence of the density of states, the homogeneity of carrier generation, and the electric field on the photocurrent onset behavior can be observed. The contribution of a higher density of states in the mobility gap to the photocurrent transients after light degradation of the sample is examined. To receive more information about the density of states in amorphous silicon solar cells the authors compare their measurements with photocurrent modeling results