Regensburg 2004 – scientific programme

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DS: Dünne Schichten

DS 21: Dünne Schichten für die Photovoltaik III

DS 21.4: Talk

Thursday, March 11, 2004, 16:30–16:45, HS 32

Fingerprints of not thermal distributed charge carriers in the photocurrent of an InP photovoltaic structure at low temperatures. — •Matthias Neges, Klaus Schwarzburg, and Frank Willig — Glienicker Str. 100, 14109 Berlin, Germany

Photocurrent excitation spectra of a InP/SnO₂ hetero junction photovoltaic device have been measured in the temperature range of 10-300 K. Below 80 K, the spectra show a periodic modulation with a beat frequency that corresponds to the LO phonon frequency. Minima in the photocurrent spectra correspond to a LO phonon cascade that scatters an electron close to the band edge. Outside this resonance, the photocurrent is enhanced with respect to the photocurrent observed at higher temperatures (>80 K).

Monte Carlo simulations reveal the principal mechanism that is responsible for the photocurrent enhancement at lower temperatures. In addition, they give insight into the energetic distribution of the photogenerated carriers. At lower temperatures, the distribution departs strongly from a thermal distribution. At room temperature, a large portion of the excess carriers is thermalized within a few 100 ps. Nonetheless, a clear deviation from a thermalized charge carrier distribution can be observed. Implications of these findings for 3rd generation photovoltaic devices will be discussed.