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(a) Light (thick curves), dark (thin), and pseudo- data (dashed). The pseudo- data ( shifted down by at 1 sun) represent the intrinsic light- free from series resistance effect and yield pseudo-efficiency and pseudo-fill factor (Ref. 10). (b) EQE data at 0 V bias. Inset: ratio of EQE at −1 and 0 V, which shows poor carrier collection efficiency for the CZTSSe cells.
(a) vs temperature data and its linear extrapolation to 0 K indicating the activation energy of the recombination process. CZTSSe cells have lower than their bandgap value. Inset: ideality factor of the CZTSSe cells vs temperature. (b) Time-resolved photoluminescence (PL) traces measured at a wavelength near bandgap that yields maximum PL signal. The plots are shifted vertically for clarity; each has a peak of counts. The minority-carrier lifetimes are obtained from curve-fitting the data using Eq. (2).
Temperature dependence of (a) efficiency and (b) dark series resistance. Inset: vs 1/T plot for back contact barrier height determination. (c) A hypothetical back contact band diagram for the CZTSSe cell, illustrating the presence of a blocking back contact. (d) Circuit model illustrating the solar cell diode , photogenerated current source , and the lumped-series resistance consisting of background or residual series resistance and a blocking back contact diode .
Device parameters for the CZTSSe cells and reference CIGS cell at room temperature. and P-FF are the pseudo-efficiency and pseudo-fill factor extracted from the pseudo- data, is the bandgap determined from the external quantum efficiency data (Ref. 8), is the series resistance measured using the light- and data (Ref. 9), is the dark series resistance [Eq. (3)], and is the dark shunt conductance at 0 V. and are the diode ideality factor and reverse saturation current determined from data. The values in parentheses are determined following Ref. 16.
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