Damp heat stability of chalcopyrite mini-modules: evaluation of specific test structures

Damp heat stress (85% relative humidity at 85°C) has been used to test long term stability of CIS thin film photovoltaic devices. Two CIS absorber types have been examined, CuInS₂ and Cu(In,Ga)Se₂. Module degradation is dominated by an increase of the series resistance R_s. In order to get information about the ZnO sheet resistance R_sq and the Mo/ZnO contact resistance R_c, which are the most important contributions to R_s, specially designed transmission-line test structures are used. Degradation of R_c strongly depends on the point of time when the second scribe for integrated series connection, P2, is made, while degradation of R_sq is strongly affected by the underlying absorber layer. Module-type solar cells without metal grid and complete mini-modules have been exposed to the same damp heat stress and yield additional information about degradation of other electrical parameters.