Some Diffusion and Solubility Measurements of Cu in CdTe

2010 35th IEEE Photovoltaic Specialists Conference

Cueto

Demtsu³

et al. 2010

The correlation of stress-induced changes in the performance of laboratory-made CdTe solar cells with various 2 nd and 3 rd level metrics is discussed. The overall behavior of aggregated data showing how cell efficiency changes as a function of open-circuit voltage (Voc), shortcircuit current density (Jsc), and fill factor (FF) is explained using a two-diode, PSpice model in which degradation is simulated by systematically changing model parameters. FF shows the highest correlation with performance during stress, and is subsequently shown to be most affected by shunt resistance, recombination and in some cases voltage-dependent collection. Large decreases in Jsc as well as increasing rates of Voc degradation are related to voltage-dependent collection effects and catastrophic shunting respectively. Large decreases in Voc in the absence of catastrophic shunting are attributed to increased recombination. The relevance of capacitancederived data correlated with both Voc and FF is discussed.

Section: Figure 1 Basic Cds/cdte Solar Cell Designsupporting

confidence: 73%

The use of 2nd and 3rd level correlation analysis for studying degradation in polycrystalline thin-film solar cells

2010 35th IEEE Photovoltaic Specialists Conference

Cueto

Demtsu³

et al. 2010

“…This assertion was also based upon the observation of Kirkendall-like voiding of the CdS layer in cells that underwent stress. In the temperature range 100-120 ºC, an activation energy of 0.63 eV was determined which agreed well with the reported value of 0.67 eV for Cu diffusion in CdTe [11].…”

Section: Introductionsupporting

confidence: 77%

Correlations of capacitance-voltage hysteresis with thin-film CdTe Solar cell performance during accelerated lifetime testing

2010 IEEE International Reliability Physics Symposium

Cueto²

2010

Abstract-In this paper we present the correlation of CdTe solar cell performance with capacitance-voltage hysteresis, defined presently as the difference in capacitance measured at zero-volt bias when collecting such data with different pre-measurement bias conditions. These correlations were obtained on CdTe cells stressed under conditions of 1-sun illumination, open-circuit bias, and an acceleration temperature of approximately 100 ºC.

“…The regression coefficients a and b were determined by the method of least squares for power-law equations [15]. The activation energy of 0.63 eV determined from the data at 100 and 120 °C is a close match to the literature value of Cu diffusion (0.67 eV) in CdTe [16]. Cu diffusion is thus implicated as being the mechanism responsible for degradation observed at higher stress temperatures.…”

Section: Resultsmentioning

confidence: 67%

“…Polycrystalline CdS/CdTe devices show good solar cell potential with laboratory efficiencies of 16.5% having been demonstrated [1]. In addition to considerable research in maximizing performance, recent work has also focused on cell stability due to concerns surrounding the use of Cu as a dopant in these structures [2,3,4].…”

Section: Introductionmentioning

confidence: 99%

Accelerated stress testing and diagnostic analysis of degradation in CdTe solar cells

2008

SPIE Proceedings

Solar cell module reliability is inextricably linked to cell-level reliability. This is particularly so with thin-film technologies. In CdTe, reliability issues historically associate with back contact stability and the use of Cu as an extrinsic dopant. Using a simple approach by which identical cells are heated under open-circuit bias and 1-sun illumination, degradation activation energies of 0.63 and 2.94 eV in laboratory-scale CdS/CdTe devices were identified in the accelerated stress temperature range of 60 to 120 °C. At lower stress temperatures, cell performance changes were linearly correlated with changes in both fill factor (FF) and short-circuit current (J sc ). At higher stress temperatures, changes in efficiency were correlated with changes in FF and open-circuit voltage (V oc ). The measured activation energy of 0.63 is associated with Cu-diffusion. During the early stage of stress testing, which may provide additional back contact annealing, improvements in FF were due to Cu-diffusion. Decreased performance observed at longer stress times (decreased FF and V oc ), according to a two-diode Pspice model, were due to both increased space-charge recombination (near the junction) and decreased recombination in the bulk. Kirkendall void formation (S-outdiffusion) at the CdS/CdTe interface is given as responsible for the 2.9 eV degradation mechanism.