Sainte-Foy-lès-Lyon, France
Sainte-Foy-lès-Lyon, France

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El-Hajje G.,Électricité de France | El-Hajje G.,Chimie Paristech | El-Hajje G.,Institute Photovoltaique Dile Of France | Ory D.,Électricité de France | And 8 more authors.
Applied Physics Letters | Year: 2016

In this letter, we investigate the origin of the spatial inhomogeneity of the photoluminescence (PL) intensity maps obtained on thin-film solar cells. Based on a hyperspectral imager setup, we record an absolute map of the quasi-Fermi level splitting Δμ by applying the generalized Planck's law. Then, using scanning confocal microscopy, we perform spatially and time-resolved photoluminescence measurements. This allowed us to quantify and map the micrometric fluctuations of the trapping defect density within these solar cells. Finally, we demonstrate the existence of a direct correlation between the spatial fluctuations of the quasi-Fermi level splitting and the trapping defect density. The latter was found to be correlated with the frequently reported spatially inhomogeneous PL maps of thin-film solar cells. Based on the observed correlation, we can quantify the local losses in quasi-Fermi level splitting induced by the spatial distribution of the trapping defects. © 2016 Author(s).


El-Hajje G.,Électricité de France | El-Hajje G.,Chimie Paristech | El-Hajje G.,Institute Photovoltaique Dile Of France | Ory D.,Électricité de France | And 10 more authors.
Solar Energy Materials and Solar Cells | Year: 2016

The authors present a contactless optical characterization method for the study of metastable defects in Cu(In,Ga)Se2 solar cells. A methodology for the analysis of time-resolved photoluminescence (TRPL) signals is presented. It leads to the observation of a hysteresis phenomenon regarding the minority carrier dynamics following the activation of the metastable defects. The amplitude of the hysteresis phenomena was compared between CIGS solar cells with different absorber/buffer layer interface properties. It is in these particular spatial regions where the metastable defects can be mostly found. The developed contactless characterization method was compared with classical current-voltage measurements. TRPL leads to a more complete understanding of the physics of metastable defects in terms of quantifying the shift in minority charge carriers dynamics that it induces. © 2015 Elsevier B.V.


El-Hajje G.,Électricité de France | El-Hajje G.,Chimie Paristech | El-Hajje G.,Institute Photovoltaique Dile Of France | Ory D.,Électricité de France | And 7 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

In the present study, we develop a contactless optical characterization tool that quantifies and maps the trapping defects density within a thin film photovoltaic device. This is achieved by probing time-resolved photoluminescence and numerically reconstructing the experimental decays under several excitation conditions. The values of defects density in different Cu(In,Ga)Se2 solar cells were extracted and linked to photovoltaic performances such as the open-circuit voltage. In the second part of the work, the authors established a micrometric map of the trapping defects density. This revealed areas within the thin film CIGS solar cell with low photovoltaic performance and high trapping defects density. This proves that the developed tool can be used to qualify and quantify the buffer layer/absorber interface properties. The final part of the work was dedicated to finding the origin of the spatial fluctuations of the thin film transport properties. To do so, we started by establishing a micrometric map of the absolute quasi-Fermi levels splitting within the same CIGS solar cell, using the hyperspectral imager. A correlation is obtained between the map of quasi-Fermi levels splitting of and the map of the trapping defects density. The latter is found to be the origin of the frequently observed spatial fluctuations of thin film materials properties. © 2016 SPIE.


Mollica F.,Électricité de France | Mollica F.,Institute Photovoltaique Dile Of France | Jubault M.,Électricité de France | Jubault M.,Institute Photovoltaique Dile Of France | And 10 more authors.
Thin Solid Films | Year: 2016

Cu(In,Ga)Se2 (CIGS) based solar cells including an ultra-thin absorber layer (<500nm) allow cost reduction but lack of sufficient generation of current. A solution would be to increase the optical path length within the CIGS absorber with a reflective back-contact. This study demonstrates that the standard Mo back-contact can be replaced by a Transparent Conducting Oxide back-contact coupled with a copper-reflector to enhance the short circuit current of cells. Simulation shows that the current density of 450nm thick CIGS can theoretically be increased up to 29.8mA/cm2 with this structure. 450 and 300nm thick coevaporated CIGS layer were deposited on ZnO:Al and SnO2:F at high temperature with an optimized NaF post-deposition treatment. The cells with the SnO2:F back contact coupled with the Cu-reflector reaches an efficiency of 11.4% for the 450nm thick CIGS and 9.5% for 300nm thick CIGS which are higher than reference cells with Mo (10.2% and 7.2% respectively). With the ZnO:Al substrate, the efficiency is lower (9.2% for 450nm thick CIGS). This is caused by a more resistive ZnO:Al/CIGS interface than SnO2:F/CIGS. Moreover, cells exhibit evidences of back surface recombination suggesting that a passivation of the back interface is required. © 2016 Elsevier B.V.

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