// Bottom device development for (flexible) tandem solar cells based on industry-compatible CIGS compound semiconductor thin films
The project aims to modify the Cu(In,Ga)Se2 cell with a view to its later use as a bottom cell in a tandem device. The overall objective is to realize a cell with 10% near infrared efficiency (780 nm long-pass filter). To achieve this goal, the absorber is optimized in terms Ga/(Ga+In) depth profile, band gap reduction down to 1 eV, surface roughness and alkali supply. For improved stability of the bottom cell against thermal stress that would occur by the later application of the top cell, magnetron sputtered buffer materials as ZnOS or Ga2O3 are used, which are not susceptible for interface-related metastability effects due to the lack of blue light in the filtered light spectrum. As a front electrode, H- and Zn-doped indium oxides with a high charge carrier mobility and a reduced absorption in the infrared wavelength region are used. All activities are accompanied by comprehensive material analysis and electro-optical characterization.
