Surface photovoltage measurement of light instability of amorphous silicon films

Abstract

The effect of prolonged light exposure on photovoltaic quality of glow discharge amorphous silicon films has been studied by the surface photovoltage technique. Two principal results have been observed. (i) The minority-carrier diffusion length degrades but stabilizes at 0.25–0.3 μm. (ii) The space-charge width collapses at open circuit voltage under as little as 0.0001 sun bias illumination. The combination of these two effects suggests that it is gross changes in the built-in electric fields that most seriously degrade the fill factor in amorphous silicon solar cells, rather than changes in μτ.

Monitoring of photodegradation and recovery of a-Si : H p-i-n solar cells by capacitance measurements

“…Since the discovery of metastable defects creation in the bandgap by Staebler and Wronski in 1977 [14], several theories have proposed the mechanism of photodegradation of a-Si : H. As stated by Epstein in [lS], "the mechanism of degradation in a a-Si : H p-i-n cells has been attributed to the decrease in the recombination lifetime associated with the observed increase in dangling Si-bond density or to the light-induced defects which act as efficient charge trapping centers". Whether lifetime or space charge is the predominant effect is still an open question, and techniques have been developed in support of the two different hypotheses [15][16][17][18]. The capacitance technique is very sensitive to space charge effects, because it monitors charge trapping in injection condition.…”

Density Of States In Amorphous Silicon

“…Special thanks are also due Dr. Bill Baron of University of Delaware, and Dr. Camille Fuleihan of Polaroid for many interesting discussions. 32 Another consequence is that the number of hole traps increases, since T -^ -> Do, and the DOS in the material is asymmetric.…”