**5.4. Reliability of Ni/Cu contacts**

Long-term reliability for Ni/Cu metal stacks is a very important feature and should be considered while evaluating the solar module lifetime. Cu is known to create deep-level impurities if diffused in silicon. Solar cell modules have to fulfil the criteria defined in the form of the IEC 61215 test [103]. The IEC 61215 requirements are to satisfy the conditions of either 1,000 hours damp-heat exposure at 85 °C with 85% relative humidity or a ≤5% *pmax* loss after 200 thermal cycles between-40 °C and 85 °C.

Limited progress in terms of reliability for the Ni/Cu contacts has been made, with few reports made so far [81-83]. Fraunhofer ISE and IMEC have tested solar modules according to the criteria defined by the IEC 61215 reliability test. Both Fraunhofer ISE and IMEC have come up with satisfactory results after damp heat exposure and thermal cycling tests [82, 83]. In another report, reliable Ni/Cu contacts for a heterojunction solar cell were presented which successfully passed the damp heat test when conducted for 3,000 hours [81]. In a report from RENA GmbH, Germany, modules comprising Ni/Cu/Sn metal stacks successfully passed the module reliability test, confirming that no Cu diffusion had occurred in the silicon [104].
