The role of the CdS buffer layer in CuGaSe2-based solar cells

We present some results for Ga-rich CuGaSe(2)-based solar cells using different conditions for deposition of the CdS buffer layer. Three different recipes for the growth of the CdS buffer layers at 60 and 80 degrees C are compared. This work shows the importance of the adaptation of the CdS growth to the absorber layer. A maximum open circuit voltage V(oc) of 922 mV is achieved by using 60 degrees C as the chemical bath temperature and lower thiourea and ammonia concentrations. Temperature-dependent current-voltage and room temperature drive-level capacitance profiling measurements are carried out to study the CdS/CuGaSe(2) interface properties. All devices are characterized by tunnelling-enhanced interface recombination. However, results show that the higher V(oc) obtained for the low bath temperature coincides with a reduced tunnelling component. This can be attributed to a lower net doping level in the space charge region. Secondary ion mass spectrometry analysis reveals Cu diffusion into the buffer layer when CdS is made at 80 degrees C. This agrees with the higher charge density observed for those devices, enhancing the tunnelling.