A new method to prepare efficient CdTe/CdS thin film backwall solar cells

An original method suitable to prepare high efficiency CdTe/CdS thin film back-wall solar cell is described. The method can be distinguished in two stages, namely: 1) the preparation of the back contact and 2) the CdTe thin film crystallization. The back contact is made by covering a 1 inch-square glass substrate with a 50-100 Å thick Cu layer followed by a 1-2 μm thick Mo layer. On top of the Mo layer a 6-10 μm thick CdTe film is deposited by sputtering or evaporation. The sample is then annealed at 500°C for two hours in a N2 flow. After the annealing the CdTe film is covered by 1-2 μm thick film of CdCl2 and then annealed again at 500°C in a N2 flow. After this treatment, the CdTe film crystallizes with a grain size larger than 20 μm. CdTe/CdS thin film solar cells prepared by using as absorbers the CdCl2-crystallized CdTe films exhibit efficiency close to 10% with open-circuit voltage varying between 600 and 760 mV, short-circuit currents between 26 and 30 mA/cm2 and fill factor around 50%.