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Current–Voltage Analysis of a‐Si and a‐SiGe Solar Cells Including Voltage‐dependent Photocurrent Collection
Author(s) -
Hegedus Steven S.
Publication year - 1997
Publication title -
progress in photovoltaics: research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.286
H-Index - 131
eISSN - 1099-159X
pISSN - 1062-7995
DOI - 10.1002/(sici)1099-159x(199705/06)5:3<151::aid-pip167>3.0.co;2-w
Subject(s) - photocurrent , optoelectronics , materials science , voltage , diode , open circuit voltage , biasing , solar cell , optics , physics , quantum mechanics
The current–voltage ( J ( V )) data measured in light and dark from a‐Si‐based solar cells have been analyzed to yield six parameters that completely specify the illuminated J ( V ) curve from reverse bias to beyond open‐circuit voltage ( V oc ). A simple photocurrent collection model is used, which assumes drift collection in a uniform field. The method has been applied to J ( V ) data from over 20 single‐junction a‐Si or a‐SiGe devices from five laboratories measured under standard simulated sunlight. Very good agreement is obtained between measured and calculated J(V) performance with only one adjustable parameter, the ratio of collection length to thickness L c / D . Some of these devices have also been analyzed after extended light soaking or under filtered illumination. The effect of the voltage‐dependent photocurrent collection on the fill factor and V oc is considered in detail. Results under 1 sun illumination for both a‐Si and a‐SiGe devices are consistent with hole‐limited collection. Photocurrent collection in very thin devices ( D ∼ 0.1 μm), or thicker devices under blue light, may be strongly influenced by interface recombination or back diffusion. The flatband voltage ( V fb ) is dependent on the intensity and spectrum of illumination, and hence is not a fundamental device property and is not equivalent to the built‐in potential. The V oc is limited by V fb , not junction recombination current J o , in typical devices. The illuminated solar cell performance is nearly independent of the forward diode current for low values of L c / D , as occurs after light soaking or with a‐SiGe. The model is also useful to investigate the intensity dependence of the fill factor and to predict the influence of L c / D and V fb on solar cell performance. © 1997 John Wiley & Sons, Ltd.