|Author's Email Address
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||Materials and Optoelectronic Science|
|Type of Document
||A study of Cu2ZnSn(S,Se)4 thin film process for photovoltaic applications|
|Date of Defense
Rapid Thermal Processing
||Adding a concentration gradient of sulfur to Cu2ZnSnSe4 to form a pentanary alloy of Cu2ZnSn(SxSe1-x)4 (CZTSSe) may modify the band structure to enhance the light absorption and also reduce the band discontinuity between the absorber layer and the buffer layer to lower the carrier transport barrier. In this work, we developed a combination of selenization and sulfurization processes to prepare CZTSSe films. Firstly, elemental precursors with a stacking sequence of (S,Se)/Cu/Sn/Zn/SLG were used for further reaction by rapid thermal annealing to form a single-phase Cu2ZnSn(S,Se)4 (CZTSSe) film. The preset composition of a precursor was Cu/(Zn+Sn)=0.75, Zn/Sn=1.3, and Se/Metal=1.3. An additional sulfur pellet weighted about 0.05g was placed in the graphite box to provide sufficient sulfur vapor during the RTA process. The heating process was done by a temperature ramp rate above 20oC/sec and kept at 530oC for 1 min. Both XRD and Raman analysis indicated that CZTSSe films could be formed under proper conditions. However, the film structures were poor for all the specimens. |
For a better control of the S/Se ratio in the film, a precursor with stacked metal films was simultaneously exposed to S and Se vapor fluxes and heated to 570oC with a temperature ramp rate of 30oC/min in a vacuum chamber. The duration of thermal annealing was 40 minutes. Indeed, the CZTSSe films were successfully prepared as expected. Further invstigations using GIXRD revealed a slight concentration gradient of sulfur in the film. Unfortunately, the film structure still needs to be improved but it may not easy due to the formation of solid phases of binary and/or ternary sulfides during the heating processes.
Since a CZTSe film with a compact grain structure can be easily prepraed in our laborotory by rapd thermal seelnization, a technique based on the interdiffusion between ZnS and CZTSe has thus been developed to produce a CZTSSe film with a desired sulfur gradient. An annealing at 400oC for 10 minutes would do the work. Auger depth profiling as well as GIXRD showed the evidences of significant interdiffusion bwtween the two materials. Although a first try on the device fabrication was not sucessful, this is still a convicing technique for future device developments.
||Mau-Phon Houng - chair|
Wei-Hung Su - co-chair
Bae-Heng Tseng - advisor
Indicate in-campus at 5 year and off-campus access at 5 year.|
|Date of Submission