Solution-processed efficient CdTe nanocrystal/CBD-CdS hetero-junction solar cells with ZnO interlayer

CdTe nanocrystal (NC)/CdS p–n hetero-junction solar cells with an ITO/ZnO-In/CdS/CdTe/MoO _x /Ag-inverted structure were prepared by using a layer-by-layer solution process. The CdS thin films were prepared by chemical bath deposition on top of ITO/ZnO-In and were found to be very compact and pin-hole free in a large area, which insured high quality CdTe NCs thin-film formation upon it. The device performance was strongly related to the CdCl₂ annealing temperature and annealing time. Devices exhibited power conversion efficiency (PCE) of 3.08 % following 400 °C CdCl₂ annealing for 5 min, which was a good efficiency for solution processed CdTe/CdS NC-inverted solar cells. By carefully designing and optimizing the CdCl₂-annealing conditions (370 °C CdCl₂ annealing for about 15 min), the PCE of such devices showed a 21 % increase, in comparison to 400 °C CdCl₂-annealing conditions, and reached a better PCE of 3.73 % while keeping a relatively high V _OC of 0.49 V. This PCE value, to the best of our knowledge, is the highest PCE reported for solution processed CdTe–CdS NC solar cells. Moreover, the inverted solar cell device was very stable when kept under ambient conditions, less than 4 % degradation was observed in PCE after 40 days storage.