Adapting Characterization Techniques for High Voc Thin-Film Tandem Solar Cells

F. VENTOSINOS; B. FAKES; E. V. JOHNSON

Aachen

Congreso; 26th International Conference on Amorphous and Nanocrystalline Semiconductors; 2015

To compete with the market standard of low-cost per Watt crystalline silicon solar cells, thin-film silicon devices must display a great leap forward in their power conversion efficiency. Multijunction devices - from the micromorph concept up to three and four junction devices - have proven to be able to reach higher efficiencies, meaning that characterization techniques for these complex structures are needed to fully understand and optimize them. In this work we focus on two techniques developed to extract the individual open circuit voltages (Voc) of tandem devices, as well as their sub-cell current voltage (IV) characteristics. These were developed to work on the micromorph cell, the subcells of which have limited regions of overlapping photoresponse due to very different band gaps. However, it is not known if such techniques will work in tandem structures consisting of very high Voc structures, such as device stacks using amorphous silicon oxide/polymorphous silicon (a-SiO:H/pmSi:H), and hydrogenated amorphous silicon(a-Si:H)/ pm-Si. These novel structures have proven to suffer from less light induced degradation (LID), which is one of the main drawbacks of devices using a-Si:H. The presence of similar band gaps (difference below 150mV in both cases) and overlapping external quantum efficiencies (EQEs) above 500nm implies that some changes have to be done in order to make these characterization techniques work.