Abstract
We deposited zinc-based films with various ammonia (ammonium hydroxide; NH4OH) and selenourea concentrations, at the bath temperature of 80 °C, on soda-lime glass substrates using the chemical bath deposition (CBD) process. We analyzed the results using X-ray photoelectron spectroscopy (XPS), which showed binding energies of zinc, selenium, and oxygen. The as-deposited films, containing zinc selenide, zinc oxide, and zinc hydroxide, were also verified. The films prepared in this investigation can be referred to a zinc compound, characterized as Zn(Se,OH). A conformal coverage of the Zn(Se,OH) films, with the smooth surface morphologies, was obtained by optimizing the ammonia or selenourea concentrations in the deposition solutions. The Zn(Se,OH) films had a preferred (111) orientation, corresponding to a cubic crystal structure. The bandgap energies of the as-deposited Zn(Se,OH) films were determined from the optical absorption data, suggesting a dependence of the bandgap energies on the atomic percentages of ZnSe, Zn(OH)2 and ZnO in the films. The same variation tendency of the compositions and the bandgap energies for the films, deposited with an increment in the ammonia or selenourea concentrations was achieved, attributing to the facilitation of ZnSe formation. These results show that the compositions, and therefore the bandgap energies, can be controlled by the ammonia concentrations, or selenourea concentrations.
Highlights
Even though various II-VI semiconductor compounds, including CdS, (Cd,Zn)S, ZnS, Zn(O,S,OH)x, ZnO, ZnSe, Inx (OH,S)y, In2 S3, etc., have been prepared by different deposition methods of chemical bath deposition (CBD), such as atomic layer deposition (ALD), ionic layer gas atomic reaction (ILGAR), metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD), or other deposition processes [3,4,5], the CdS buffer layers prepared by the CBD method achieved the best performance of CIGS-based solar cells
One of the important requirements for the buffers of the CIGS solar cells is to provide a well coverage on the top of CIGS films, which facilitates the formation of the electric junction and prohibits the formation of the shunt path between the AZO and CIGS layers
The compositions of the Zn(Se,OH) films deposited with various ammonia or selenourea concentrations were analyzed by conducting the deconvolution of the photoelectron binding energy spectra as follows
Summary
The Cu(In,Ga)Se2 (CIGS) solar cells prepared by the co-evaporation process [1], and the. Cu(In,Ga)(Se,S) (CIGSS) solar cells prepared by the sulfurization after selenization (SAS) process [2], employed a thin CdS film as the buffers have reached the conversion efficiencies of over 22%. The CIGS-based solar cells, with the CBD CdS buffers, have reached the efficiencies of greater than 22% [1,2]. The active-area efficiency of the CIGSS solar cell with the ZnSe buffer was reported to be 15.7% [9,10]. Employed a Zn(OH)2 /Zn(Se,OH) buffer for the CIGSS solar cells, and achieved the total-area efficiency of 14.4% [11]. In terms of efficiency for the CIGS solar cells, the buffer layers are required to provide a uniform coverage on the top of the CIGS films, and to avoid the formation of the shunt path between the CIGS and the ZnO:Al (AZO) layers. The coverage of buffers was assessed by analyzing the FESEM (field emission scanning electron microscopy) images of surface morphology for the as-deposited Zn(Se,OH) films
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
