Chalcopyrites Thin film solar cells
We are focused on the investigation of highly efficient and stable thin film solar cells absorbers, such as chalcopyrites Cu(In,Ga)Se2 and Cu(In,Ga)S2. At the heart of our research lies photoluminescence (PL), a powerful tool that enables us to analyze the electronic structure of semiconductor films and predict their suitability for use in efficient solar cells.
Growing and Analysing Thin Films
Predicting – Understanding – Improve
By exciting electrons from the valence band to the conduction band with a laser beam, we can measure the luminescence emitted as they recombine. This allows us to determine the concentration of electrons available in the solar cell.
With intensity and spectrally calibrated PL, which allows photon counting, we can determine the internal voltage of the semiconductor, the so-called quasi-Fermi level splitting. Another technique called time-resolved PL having nanosecond resolution, is used to measure how long the light-generated electrons remain in their excited state and are available for the solar cell.
The solar spectrum is not efficiently used in single solar cells as the light with photon energies below the bandgap of the is lost and the light with high energies is not used efficiently, due to thermalisation. By stacking two (or more) solar cells, we can reduce both of these losses: the top solar cell (with a high bandgap) makes more efficient use of the high energy photons and lets the lower energy ones pass to the bottom solar cell (with a lower band gap) that uses more of them than a stand-alone cell. Therefore, sulphide chalcopyrites Cu(In,Ga)S2 which have a high bandgap and CuInSe2, which have a low bandgap are suitable candidates for tandem solar cell device