INTRODUCTION OF COPPER BY WET DEPOSITION IN CDTE SOLAR CELLS

CdTe thin film solar cells have reached an efficiency of 22.1%. These solar cells are generally fabricated adding copper to the absorber. Despite different copper-free back contacts have been introduced, the presence of copper has demonstrated to deliver the highest efficiency. On the other hand, Cu is a fast diffuser in CdTe, leading to the formation of carrier traps and resulting in degradation of the devices. For this reason a suitable Cu concentration and the formation of a stable back contact are very important to reach high efficiency and stability. In this paper, a copper chloride wet deposition method has been developed, and a comparison between the addiction of copper through vacuum evaporation and wet deposition is presented. Through a solution, the deposition uniformity of a very small amount of copper can be easily controlled. Moreover, with this method the obtained efficiencies are higher than with same quantity of evaporated copper, and are very similar to the device with larger quantity of evaporated copper but with a dramatic stability improvement.