High temperature CSS processed CdTe solar cells on commercial SnO₂:F/SnO₂ coated soda-lime glass substrates

We report on the realization of CdS/CdTe solar cells grown on commercial SnO₂:F/SnO₂-coated soda-lime glass substrates with conversion efficiencies >16 % by careful optimization of fabrication processes, which consist of sequential deposition of magnetron sputtered CdS window layer and high temperature close-space sublimation of CdTe absorber, CdCl₂ activation, and thermal evaporation of elemental Cu/Au bilayer back contacts. The optimization of CdS and CdTe depositions include the incorporation of small fraction of oxygen during the growth. In our fabrication, the optimal amount of O in the deposition ambient is 5 % for CdS deposition and 0.5 % for CdTe depositions. The incorporation of small amounts of O is found to enhance the short circuit current (J_SC) and open circuit voltage (V_OC) of CdTe solar cells. We further identified that the flow rate of the ambient gas during the CdS sputtering can also affect the performance of the CdTe solar cells. The optimal flow rate is 40 sccm for our fabrication process. With careful optimization of our synthesis steps, the best small-area cell has shown an efficiency of 16.4 % with a V_OC of 858 mV, a J_SC of 26.5 mA/cm², and a fill-factor of 72.0 % measured under AM1.5G illumination. This cell was coated with a 100 nm thick magnesium fluoride anti-reflection coating layer on the glass side.