Complex Surface Chemistry of Kesterites: Cu/Zn Reordering after Low Temperature Postdeposition Annealing and Its Role in High Performance Devices
2015 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 15, 5279-5287 p.Article in journal (Refereed) Published
A detailed study explaining the beneficial effects of low temperature postdeposition annealing combined with selective surface etchings for Cu2ZnSnSe4 (CZTSe) based solar cells is presented. After performing a selective oxidizing surface etching to remove ZnSe secondary phases typically formed during the synthesis processes an additional 200 degrees C annealing step is necessary to increase device performance from below 3% power conversion efficiency up to 8.3% for the best case. This significant increase in efficiency can be explained by changes in the surface chemistry which results in strong improvement of the CdS/CZTSe heterojunction commonly used in this kind of absorber/buffer/window heterojunction solar cells. XPS measurements reveal that the 200 degrees C annealing promotes a Cu depletion and Zn enrichment of the etched CZTSe absorber surface relative to the CZTSe bulk. Raman measurements confirm a change in Cu/Zn ordering and an increase in defect density. Furthermore, TEM microstructural investigations indicate a change of grain boundaries composition by a reduction of their Cu content after the 200 degrees C annealing treatment. Additionally, insights in the CdS/CZTSe interface are gained showing a significant amount of Cu in the CdS buffer layer which further helps the formation of a Cu-depleted surface and seems to play an important role in the formation of the pn-heterojunction.
Place, publisher, year, edition, pages
2015. Vol. 27, no 15, 5279-5287 p.
Materials Chemistry Engineering and Technology
IdentifiersURN: urn:nbn:se:uu:diva-261958DOI: 10.1021/acs.chemmater.5b01473ISI: 000359499100016OAI: oai:DiVA.org:uu-261958DiVA: diva2:855469