Spectral behavior of solar cells based on the ‘‘junction near local defect layer’’ design

Abstract

The junction near local defect layer (JNLD) solar cell design [Li et al., Appl. Phys. Lett. 60, 2240 (1992)] was recently shown to greatly increase the short circuit current of silicon solar cells. The proposed mechanism is an enhancement of sub-band-gap light absorption through gap states, introduced by the presence of a defect layer situated in the junction region. Our measurements of JNLD solar cells evidence a change in the absorption spatial profile due to the defect layer. The result is a small enhancement in quantum efficiency in the visible red side of the spectrum that is in turn balanced by a recombination effect caused by the same defect layer, so that the final short circuit current does not increase. On the contrary, we detected a 20% decrease in the open circuit voltage that is attributed to the shorting effect of defect levels in the junction region. No sub-band-gap light absorption increase is detected.