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Influence of Ga/(Ga + In) grading on deep‐defect states of Cu(In,Ga)Se 2 solar cells
Author(s) -
Kotipalli Ratan,
Vermang Bart,
Fjällström Viktor,
Edoff Marika,
Delamare Romain,
Flandre Denis
Publication year - 2015
Publication title -
physica status solidi (rrl) – rapid research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.786
H-Index - 68
eISSN - 1862-6270
pISSN - 1862-6254
DOI - 10.1002/pssr.201510024
Subject(s) - copper indium gallium selenide solar cells , gallium , solar cell , indium , analytical chemistry (journal) , optoelectronics , materials science , deep level transient spectroscopy , capacitance , chemistry , silicon , electrode , chromatography , metallurgy
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 V oc is found to be the deep‐defect density close to the space charge region (SCR). In ungraded devices, high deep‐defect concentrations (4.2 × 10 16 cm –3 ) were observed near the SCR, offering a source for Shockley–Read–Hall recombination, reducing the cell's V oc . In graded devices, the deep‐defect densities near the SCR decreased by one order of magnitude (2.5 × 10 15 cm –3 ) for back surface graded devices, and almost two orders of magnitude (8.6 × 10 14 cm –3 ) for double surface graded devices, enhancing the cell's V oc . 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. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)