Improving The Performance Of CdTe Nanocrystals Solar Cells By Adjusting The Anode Interface

Cadmium telluride(CdTe)nanocrystals solar cells fabricated by solution method have attracted great attention and vigorous development due to its simple preparation process,low-cost and stable performance.CdTe is a direct bandgap semiconductor with a band gap of1.45 eV and high optical absorption coefficient.It is an ideal solar cell material.At present,with the improvement of device technology and the optimization of structure,the power conversion efficiency of CdTe nanocrystals solar cells has reached more than 10%,but there is still a certain distance compared with the traditional close-space sublimation method of CdTe solar cells(usually between 14%and 17%,up to 22%).The key problems are low open-circuit voltage(usually less than 0.7 V)and low short-circuit current(less than 20mA/cm~2).The main reason for these problems is that the back contact and interface treatment of the solar cells have not reached a high level,resulting in excessive carrier recombination,which reduces the overall performance of the device.Therefore,this paper mainly focuses on interface engineering of CdTe films,improving the separation and collection efficiency of carriers,and ultimately obtaining nanocrystals solar cells with high conversion efficiency.The main work of this paper is as follows:1.Triphenylamine conjugated polymer(Si-TPA)with high power function is introduced for the first time as a hole transport layer to realize the efficient separation of carriers.The prepared inverted CdTe nanocrystals solar cells is ITO/ZnO/CdSe/CdTe/Si-TPA/Au.After optimization,the short circuit current of the device is 23.38 mA/cm~2,the open circuit voltage is 0.66 V,and the filling factor is 54.05%and the corresponding PCE is 8.34%,which is the best level of CdTe nanocrystals solar cells with inverted structure reported before.At the same time,we applied Si-TPA to another structure of nanocrystals solar cells(ITO/ZnO/CdS/CdTe/Si-TPA/Au),which also achieved a high efficiency of 7.28%,significantly higher than those without any hole transport layer(~5%)or other hole transport layer(4%).2.For the first time,we have developed an acid vapor surface etching process for the etching of CdTe.The preparation of Te-rich layer on the surface of CdTe has been successfully realized,and the Schottky barrier at the back interface of the device has been reduced.It is found that the acid vapor etching process we used has a wide range of adaptability,whether using bromine-methanol solution(BM)or nitric-acetic acid solution(NA)has achieved good results.The device treated by NA etching has an efficiency of 8.67%and the BM etching efficiency of 8.38%.Moreover,the etched CdTe device has a high stability.It has been placed at room temperature and open environment for more than 1months without any degradation of performance,which lays a good foundation for further commercial application of such devices.