CdTe thin film solar cells with reduced CdS film thickness

A study was performed to reduce the CdS film thickness in CdTe thin film solar cells to minimize losses in quantum efficiency. Using close space sublimation deposition for CdS and CdTe a maximum efficiency of ∼ 9.5% was obtained with the standard CdS film thickness of ∼ 160 nm. Reduction of the film CdS thickness to less than 100 nm leads to poor cell performance with ∼ 5% efficiency, mainly due to a lower open circuit voltage. An alternative approach has been tested to reduce the CdS film thickness (∼ 80 nm) by depositing a CdS double layer. The first CdS layer was deposited at high substrate temperature in the range of 520-540 °C and the second CdS layer was deposited at low substrate temperature of ∼ 250 °C. The cell prepared using a CdS double layer show better performance with cell efficiency over 10%. Quantum efficiency measurement confirmed that the improvement in the device performance is due to the reduction in CdS film thickness. The effect of double layer structure on cell performance is also observed with chemical bath deposited CdS using fluorine doped SnO₂ as substrate.