Field collapse due to band-tail charge in amorphous silicon solar cells

Qi Wang, Richard S. Crandall, Eric Allan Schiff

Research output: Chapter in Book/Entry/PoemConference contribution

9 Scopus citations


It is common for the fill factor to decrease with increasing illumination intensity in hydrogenated amorphous silicon solar cells. This is especially critical for thicker solar cells, because the decrease is more severe than in thinner cells. Usually, the fill factor under uniformly absorbed red light changes much more than under strongly absorbed blue light. The cause of this is usually assumed to arise from space charge trapped in deep defect states. We model this behavior of solar cells using the Analysis of Microelectronic and Photonic Structures (AMPS) simulation program. The simulation shows that the decrease in fill factor is caused by photogenerated space charge trapped in the band-tail states rather than in defects. This charge screens the applied field, reducing the internal field. Owing to its lower drift mobility, the space charge due to holes exceeds that due to electrons and is the main cause of the field screening. The space charge in midgap states is small compared with that in the tails and can be ignored under normal solar-cell operating conditions. Experimentally, we measured the photocapacitance as a means to probe the collapsed field. We also explored the light intensity dependence of photocapacitance and explain the decrease of FF with the increasing light intensity.

Original languageEnglish (US)
Title of host publicationConference Record of the IEEE Photovoltaic Specialists Conference
Editors Anon
PublisherIEEE Computer Society
Number of pages4
StatePublished - 1996
Externally publishedYes
EventProceedings of the 1996 25th IEEE Photovoltaic Specialists Conference - Washington, DC, USA
Duration: May 13 1996May 17 1996


OtherProceedings of the 1996 25th IEEE Photovoltaic Specialists Conference
CityWashington, DC, USA

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Condensed Matter Physics


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