Light Induced Degradation in PERC Solar Cells and comparison with OxyMap

Transcription

1 Light Induced Degradation in PERC Solar Cells and comparison with OxyMap J. Arumughan 1, B. Martel 2, G. Raymond 2, S. Schmitt 1, J. Theobald 1, C. Picoulet 3, X. Brun 3, R. Kopecek 1 1 International Solar Energy Research Center - ISC Konstanz, Rudolf-Diesel Str.15, D Konstanz, Germany 2 CEA/LITEN/DTS, INES, 50 avenue du Lac Léman, Le Bourget du Lac, France 3 AET Technologies, 8 Chemin de Malacher, Inovallée, Meylan, France

2 Contents Introduction Experimental Light induced degradation OxyMap tool for Oxygen characterization and LID predictions Summary 2

3 Introduction - Increased efficiency due to better passivation and higher reflection of rear side - An advantage of the PERC solar cells is that the process sequence is largely compatible with the process of Al-BSF cells - PERC is gaining market share and might become the next main stream product - One of the important aspects that has to be addressed is the LID in PERC 3

4 Materials used in this study Group t [µm] ρ [Ω-cm] [Oi] (FTIR ASTM ) (ppma) I II III IV >12 - Four different Czochralski Silicon material are used - Group I and Group II are essentially the same material, but varying thicknesses - Group III and Group IV are low resistivity materials, but varying [O i ] concentrations - PERC solar cells are processed and characterized, and the neighboring wafers were chosen for 'OxyMap' measurements 4

5 PERC solar cell results - V oc of the groups I and II are identical due to the similar material properties - V oc values are lower for groups III and the lowest for the group IV - Lower J sc for low base resistivities 5

6 PERC solar cell results - High fill factor values for low base resistivity material - Efficiency between 19.1 % % for (higher base resistivity) - Efficiency between 19.2 % % for G.III (low base resistivity) due to higher FF - Lowest efficiency for group IV low base resistivity and high [O i ] 6

7 Cell results - Group IV with highest oxygen concentration deviate from other groups difference in material quality 7

8 LID in PERC - Simultaneous testing capacity of the cells - Maximum test area: 160 x160 mm - Temperature range for the testing of the cells: C - Spectral quality of the lamp: Class B - Maximum irradiance in test area: 1000 Wm-² LID Tester available at: 8

9 B-O (cm -3 ) LID in PERC LID at 25 C - Measurements at 25 C - PERC solar cells with lower base resistivities degrade higher than the samples with higher base resistivities - Group IV PERC cell with highest [O i ] concentration shows the highest degradation - PV 2000 measurements confirm B-O concentration in different groups K. Bothe, R. Sinton, J. Schmidt, Progress in Photovoltaic: Research and Application 2005; 13:

10 LID in PERC LID at 25 C LID at 70 C - Measurements at 70 C simulation of module temperature - Strong trend in regeneration in group 3 where the base resistivity and O i concentration are low. - Regeneration process occurs at lower rates as already mentioned on Al-BSF cells* *A. Herguth et al, Proceeding IEEE conference (2006) 10

11 LID and Regeneration in PERC - LID for 120 hrs - Regeneration performed at 120 C for 4 hours - Cells regain close to the initial levels 11

12 OxyMap Process Overview High T r 450 C 1 r 2 r anneal anneal 3 [TD] ini (as-grown) [O i ] Intentional Dopant concentration ([B], [P] ) Degraded lifetime after LID (t BO ) Cell LID predictions - OxyMap provides an accurate charaterization of [B] and [O i ] in the Cz wafers and proposes some models to predict the cells efficiency degradation after B-O formation 12

13 OxyMap LID Models [B] + [Oi] Carrier lifetime limited by B-O complexes* Semi-empirical model based on PC1D simulation and experimental data from CEA-INES PERC cells Prediction of the LID losses due to BO complexes (DV oc, DJ sc, DFF, DEfficiency) + LID amplitude - *K. Bothe, R. Sinton, J. Schmidt, Fundamental Boron-Oxygen-related Carrier Lifetime Limit in Mono and multicrystalline Silicon Progress in Photovoltaic: Research and Application 2005; 13:

14 [O i ]: OxyMap vs FTIR [ O i ] (ppma) The remaining slight differences might be explained by : [ O i ] (ppma) Group (FTIR, ASTM F121-83) (OxyMap converted to F121-83) I II III IV > Good agreement between both OxyMap and FTIR measurements on thick neighboring samples -A difference of location between OxyMap and FTIR samples and thus be justified by common fluctuations of the [O i ] through the ingot height - A difference of standards (OxyMap calibrated with SEMI MF , FTIR using a more tolerant coefficient following ASTM F121-83) 14

15 OxyMap and I-V after LID OxyMap predictions (based on wafers) Group J sc (%) V oc (%) FF (%) η(%) I II III IV Measured I-V parameters of PERC solar cells after LID at 25 C. Group J sc (%) V oc (%) FF (%) η(%) I II III IV OxyMap and I-V measurements after LID follow the same trend: The higher the [O i ] and the [B], the higher the LID amplitude - Despites low [O i ], the fabricated PERC cells features high LID loss compared to what is predicted in OxyMap models - Discrepancies due to differences between the experimental and simulated cells architectures can be reduced by recalibration procedure proposed in OxyMap tool 15

16 LID predictions after correction - Fair agreement between the calibrated model and the experimental LID loss - Even if re-calibrated, the model keep the correlation between LID loss amplitude and [B] and [O i ] 16

17 Summary and Outlook - The LID behavior of PERC solar cells was studied for different Cz Silicon materials -The LID at 25 C follow the expected trend: -Low base resistivity material => Higher LID loss -Low base resistivity with high [O i ] => Highest LID loss - Simulated module temperature at 70 C shows slow regeneration. The regeneration is exceptionally fast for group III PERC cells - OxyMap and FTIR measurements of [Oi] are in good agreement -The LID predicted by OxyMap measurements and I-V measurements after LID follow the same trend - The OxyMap can be calibrated according to the specific cell architecture 17

18 Ackowledgements Dr. Thomas Pernau (Centrotherm) Mr. Jan Lossen Mrs. Lejlja Hildebrand Mr. Rafael Marczak Mr. Sascha Grani Mr. Stephan Eisert Mr. Zih Wei Peng 18

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