Influence of Ga/(Ga plus In) grading on deep-defect states of Cu(In, Ga)Se-2 solar cells
2015 (English)In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 9, no 3, 157-160 p.Article in journal (Refereed) Published
The benefits of gallium (Ga) grading on Cu(In, Ga) Se-2 (CIGS) solar cell performance are demonstrated by comparing with ungraded CIGS cells. Using drive-level capacitance profiling (DLCP) and admittance spectroscopy (AS) analyses, we show the influence of Ga grading on the spatial variation of deep defects, free-carrier densities in the CIGS absorber, and their impact on the cell's open-circuit voltage V-oc. The parameter most constraining the cell's Voc is found to be the deep-defect density close to the space charge region (SCR ). In ungraded devices, high deep-defect concentrations (4.2 x 1016 cm(-3)) were observed near the SCR, offering a source for Shockley Read-Hall recombination, reducing the cell's Voc. In graded devices, the deep-defect densities near the SCR decreased by one order of magnitude (2.5 x 1015 cm(-3)) for back surface graded devices, and almost two orders of magnitude (8.6 x 1014 cm(-3)) for double surface graded devices, enhancing the cell's Voc. In compositionally graded devices, the free-carrier density in the absorber's bulk decreased in tandem with the ratio of gallium to gallium plus indium ratio GGI = Ga/(Ga + In), increasing the activation energy, hindering the ionization of the defect states at room temperature and enhancing their role as recombination centers within the energy band.
Place, publisher, year, edition, pages
2015. Vol. 9, no 3, 157-160 p.
gallium, deep levels, defects, admittance spectroscopy, CuInGaSe2, solar cells
Research subject Engineering Science with specialization in Electronics
IdentifiersURN: urn:nbn:se:uu:diva-252029DOI: 10.1002/pssr.201510024ISI: 000351674600001OAI: oai:DiVA.org:uu-252029DiVA: diva2:809144