Solar Cells Active in Complete Darkness - Advances in Thin-Film Solar Cells - page 165

device.Thedesignwasexperimentallytestedwithawell-researched
material system, MOVPE-grown Al x Ga (1 − x ) As. The highest-reported
open circuit voltages of ∼ 1,175 mV with the highest possible FF
values (0.83-0.87) have been observed [1, 3] for the first two
growths and fabrication. While the work is continuing to increase
short circuit current density values, these devices were tested to
explore the experimental evidence of the impurity PV effect, as
expected from this design. Measurements of responsivity and PV
activity in dark conditions have been carried out to investigate the
impurity PV effect in these devices. Responsivity measurements
indicate the current collection in the IR region, confirming the
contribution from IR photons. The I-V measurements under dark
conditions produced open circuit voltages exceeding 750 mV,
confirming the contribution from the surrounding heat radiation.
The new features of graded bandgap devices enable the impurity
PV effect to dominate the detrimental recombination process and
create useful charge carriers. This is possiblebecause ofthe desired
shape of the energy band edges present in the structure, which
creates a high electric field within the device for the effective
separation and collection of charge carriers.
References
1. I. M. Dharmadasa (2005) Sol. Energy Mater. Sol. Cells , 85 , 293.
2. I. M. Dharmadasa, J. S. Roberts, and G. Hill (2005) Sol. Energy Mater. Sol.
Cells , 88 , 413.
3. I. M. Dharmadasa, G. J. Tolan, J. S. Roberts, G. Hill, S. Ito, P. Liska, and
M. Gratzel (June 2006) Proceedings of the 21st European Photovoltaic
Conference, Dresden, Germany.
4. I. M. Dharmadasa, O. Elsherif, and G. J. Tolan (6-10 September
2010) Proceedings of the 5th World Photovoltaic Conference and 25th
European Photovoltaic Conference, Valencia, Spain.
5. M. A. Green, K. Emery, D. L. King, S. Igari, and W. Warta (2005) Prog.
Photovolt: Res. Appl. , 13 , 49.
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[546.681'62'19:546. 681'19].