Breakdown characteristics of flexible Cu(In,Ga)Se2 solar cells

• We examine reverse bias behavior of CIGSe solar cells.
• Influence of illumination and temperature on breakdown is analyzed.
• We show that tunnel breakdown is main breakdown mechanism.
• Proof of tunnel breakdown by two independent measurements (IVT and CV).
• A first reverse bias electroluminescence measurement of CIGSe is shown.

The behavior of solar cells under reverse bias conditions is of crucial importance for solar module design and stability. For flexible, low temperature deposited Cu(In,Ga)Se2 (CIGSe) solar cells indications for tunnel breakdown at operation temperatures around 300 K are found using temperature and net carrier concentration dependent measurements of the breakdown voltage VBR. For temperatures below 200 K, the temperature coefficient of the breakdown voltage becomes positive, indicating a change of the breakdown mechanism to avalanche breakdown. A reduction of VBR caused by the illumination with blue photons is demonstrated, which coincides well with results and models for high temperature deposited CIGSe on glass. Furthermore, spectrally resolved measurements of light emission during breakdown indicate a first ReBEL (reverse bias electroluminescence) signature for CIGSe solar cells.