A possible way to reduce absorber layer thickness in thin film CdTe solar cells

Reducing the thin film module production cost is a strong focus in the current thin film solar cell research. One possible way to reduce the cost is minimising material consumption by reducing film thickness. Ultra thin CdTe layer will also help to design p–i–n structure solar cells. The standard CdTe layer thickness is normally in the range of 4–5 μm. Experimental trials were carried out in order to reduce the CdTe layer thickness below 1 μm using close spaced sublimation technique. Simply reducing the CdTe layer thickness induces pinholes in the CdTe layer which results in poor device performance. The film thickness reduction below 1.5 μm was achieved by employing a double layer structure. In the process of making CdTe double layer the first layer was deposited at higher substrate temperature (~ 520 °C) and the second layer was deposited at low substrate temperature (~ 350 °C). The maximum cell efficiency of 12.5% was obtained for ~ 3 μm CdTe layer and comparable device performance was obtained for the 1.5 μm CdTe layer (11.2%). Further reducing the film thickness below 1.5 μm reduces the device performance. Solar cell efficiencies for ~ 0.8 μm and 0.5 μm CdTe layers were 9.5% and 5.2% respectively. The Capacitance–Voltage measurements show that the CdTe layer is fully depleted when the thickness is reduced below 1 μm. Further, the possible cause for the decrease in efficiency with decrease in CdTe film thickness is discussed in this article.

► Preparation of ultra thin CdTe layer film by Close Spaced Sublimation.
► CdTe double layer structure was employed to achieve pinhole free CdTe layers.
► CdTe film thickness reduction up to 1.5 μm is possible without loss in efficiency.