[en] Record efficiency in chalcopyrite-based solar cells Cu(In,Ga)(S,Se)2 is achieved using a gallium gradient to increase the bandgap of the absorber toward the back side. Although this structure has successfully reduced recombination at the back contact, we demonstrate that in industrial absorbers grown in the pilot line of Avancis, the back part is a source of non-radiative recombination. Depth-resolved photoluminescence (PL) measurements reveal two main radiative recombination paths at 1.04 eV and 1.5–1.6 eV, attributed to two phases of low and high bandgap material, respectively. Instead of a continuous change in the bandgap throughout the thickness of the absorber, we propose a model where discrete bandgap phases interlace, creating an apparent gradient. Cathodoluminescence and Raman scattering spectroscopy confirm this result. Additionally, deep defects associated with the high gap phase reduce the absorber's performance. Etching away the back part of the absorber leads to an increase of one order of magnitude in the PL intensity, i.e., 60 meV in quasi-Fermi level splitting. Non-radiative voltage losses correlate linearly with the relative contribution of the high energy PL peak, suggesting that reducing the high gap phase could increase the open circuit voltage by up to 180 mV.
MELCHIORRE, Michele ; University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Physics and Materials Science (DPHYMS)
Dingwell, Felix; Laboratory for Photovoltaics, Physics and Materials Science Research Unit, University of Luxembourg 1 , 41 rue du Brill, Belvaux L-4422, Luxembourg
ELANZEERY, Hossam ; University of Luxembourg > Faculty of Science, Technology and Medicine > Department of Physics and Materials Science > Department of Physics and Materials Science ; AVANCIS GmbH 2 , Otto-Hahn-Ring 6, 81739 München, Germany
LOMUSCIO, Alberto ; University of Luxembourg > Faculty of Science, Technology and Medicine > Department of Physics and Materials Science > Team Susanne SIEBENTRITT ; AVANCIS GmbH 2 , Otto-Hahn-Ring 6, 81739 München, Germany
Guc, Maxim ; Catalonia Institute for Energy Research (IREC) 3 , Jardins de les Dones de Negre 1, 2a pl., 08930 Sant Adrià de Besòs, Barcelona, Spain
Fonoll-Rubio, Robert ; Catalonia Institute for Energy Research (IREC) 3 , Jardins de les Dones de Negre 1, 2a pl., 08930 Sant Adrià de Besòs, Barcelona, Spain
Izquierdo-Roca, Victor ; Catalonia Institute for Energy Research (IREC) 3 , Jardins de les Dones de Negre 1, 2a pl., 08930 Sant Adrià de Besòs, Barcelona, Spain
Kusch, Gunnar ; Department of Materials Science and Metallurgy, University of Cambridge 4 , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
Oliver, Rachel A. ; Department of Materials Science and Metallurgy, University of Cambridge 4 , 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
SIEBENTRITT, Susanne ; University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Physics and Materials Science (DPHYMS)
Press release: New world record for thin-film modules ( 2023).
NREL, Best research-cell efficiencies ( 2023).
M. Nakamura, K. Yamaguchi, Y. Kimoto, Y. Yasaki, T. Kato, and H. Sugimoto, “ Cd-free Cu(In,Ga)(Se,S)2 thin-film solar cell with record efficiency of 23.35%,” IEEE J. Photovoltaics 9( 6), 1863- 1867 ( 2019). 10.1109/jphotov.2019.2937218
M. A. Contreras, J. Tuttle, A. Gabor, A. Tennant, K. Ramanathan, S. Asher, A. Franz, J. Keane, L. Wang, and R. Noufi, “ High efficiency graded bandgap thin-film polycrystalline Cu(In,Ga)Se2-based solar cells,” Sol. Energy Mater. Sol. Cells 41-42, 231- 246 ( 1996). 10.1016/0927-0248(95)00145-x
M. Bodegård, O. Lundberg, J. Malmstrom, L. Stolt, and A. Rockett, “ High voltage Cu(In,Ga)Se, devices with Ga-profiling fabricated using co-evaporation,” in Conference Record of the Twenty-Eighth IEEE Photovoltaic Specialists Conference ( IEEE, 2000).
A. M. Gabor, J. R. Tuttle, M. H. Bode, A. Franz, A. L. Tennant, M. A. Contreras, R. Noufi, D. G. Jensen, and A. M. Hermann, “ Band-gap engineering in Cu(In,Ga) Se2 thin films grown from (In,Ga)2 Se3 precursors,” Sol. Energy Mater. Sol. Cells 41-42, 247- 260 ( 1996). 10.1016/0927-0248(95)00122-0
T. Wang, F. Ehre, T. P. Weiss, B. Veith-Wolf, V. Titova, N. Valle, M. Melchiorre, O. Ramírez, J. Schmidt, and S. Siebentritt, “ Diode factor in solar cells with metastable defects and back contact recombination,” Adv. Energy Mater. 12( 44), 2202076 ( 2022). 10.1002/aenm.202202076
W. Shockley and H. J. Queisser, “ Detailed balance limit of efficiency of p-n junction solar cells,” J. Appl. Phys. 32( 3), 510- 519 ( 1961). 10.1063/1.1736034
S. Siebentritt, T. P. Weiss, M. Sood, M. H. Wolter, A. Lomuscio, and O. Ramirez, “ How photoluminescence can predict the efficiency of solar cells,” J. Phys.: Mater. 4( 4), 042010 ( 2021). 10.1088/2515-7639/ac266e
M. A. Green and A. W. Y. Ho-Baillie, “ Pushing to the limit: Radiative efficiencies of recent mainstream and emerging solar cells,” ACS Energy Lett. 4( 7), 1639- 1644 ( 2019). 10.1021/acsenergylett.9b01128
J. Palm, T. Dalibor, R. Lechner, S. Pohlner, R. Verma, R. Dietmüller, A. Heiß, H. Vogt, and F. Karg, in 29th European Photovoltaic Solar Energy Conference and Exhibition, 2014.
V. Probst, W. Stetter, W. Riedl, H. Vogt, M. Wendl, H. Calwer, S. Zweigart, K. D. Ufert, B. Freienstein, H. Cerva, and F. H. Karg, “ Rapid CIS-process for high efficiency PV-modules: Development towards large area processing,” Thin Solid Films 387( 1-2), 262- 267 ( 2001). 10.1016/s0040-6090(00)01800-9
M. H. Wolter, B. Bissig, E. Avancini, R. Carron, S. Buecheler, P. Jackson, and S. Siebentritt, “ Influence of sodium and rubidium postdeposition treatment on the quasi-fermi level splitting of Cu(In,Ga)Se2 thin films,” IEEE J. Photovoltaics 8( 5), 1320- 1325 ( 2018). 10.1109/jphotov.2018.2855113
S. Lange, F. Giesl, V. Naumann, C. Hagendorf, and P. Eraerds, “ Exfoliation methods for compositional and electronic characterization of interfacial Mo(Sex,Sy) in Cu(In,Ga)(Se,S)2 solar cells by X-ray and UV photoelectron spectroscopy,” Surf. Interface Anal. 54, 688 ( 2022). 10.1002/sia.7081
L. Weinhardt, O. Fuchs, A. Peter, E. Umbach, C. Heske, J. Reichardt, M. Bär, I. Lauermann, I. Kötschau, A. Grimm, S. Sokoll, M. C. Lux-Steiner, T. P. Niesen, S. Visbeck, and F. Karg, “ Spectroscopic investigation of the deeply buried Cu (In,Ga) (S,Se)2/Mo interface in thin-film solar cells,” J. Chem. Phys. 124( 7), 074705 ( 2006). 10.1063/1.2168443
R. Scheer and H.-J. Lewerenz, “ Formation of secondary phases in evaporated CuInS2 thin films: A surface analytical study,” J. Vac. Sci. Technol., A 13( 4), 1924- 1929 ( 1995). 10.1116/1.579631
J. Lähnemann, J. F. Orri, E. Prestat, D. N. Johnstone, and N. Tappy, LumiSpy/lumispy: v0.2.1 ( 2022).
M. Bär, W. Bohne, J. Röhrich, E. Strub, S. Lindner, M. C. Lux-Steiner, C. H. Fischer, T. P. Niesen, and F. Karg, “ Determination of the band gap depth profile of the penternary Cu(In(1-x)Gax)(SySe(1-y))2 chalcopyrite from its composition gradient,” J. Appl. Phys. 96( 7), 3857- 3860 ( 2004). 10.1063/1.1786340
J. Tauc, R. Grigorovici, and A. Vancu, “ Optical properties and electronic structure of amorphous germanium,” Phys. Status Solidi 15, 627 ( 1966). 10.1002/pssb.19660150224
E. A. Davis and N. F. Mott, “ Conduction in non-crystalline systems V. Conductivity, optical absorption and photoconductivity in amorphous semiconductors,” Philos. Mag. 22( 179), 903- 922 ( 1970). 10.1080/14786437008221061
R. Carron, C. Andres, E. Avancini, T. Feurer, S. Nishiwaki, S. Pisoni, F. Fu, M. Lingg, Y. E. Romanyuk, S. Buecheler, and A. N. Tiwari, “ Bandgap of thin film solar cell absorbers: A comparison of various determination methods,” Thin Solid Films 669, 482- 486 ( 2019). 10.1016/j.tsf.2018.11.017
J. Keller, R. Schlesiger, I. Riedel, J. Parisi, G. Schmitz, A. Avellan, and T. Dalibor, “ Grain boundary investigations on sulfurized Cu(In,Ga)(S,Se)2 solar cells using atom probe tomography,” Sol. Energy Mater. Sol. Cells 117, 592- 598 ( 2013). 10.1016/j.solmat.2013.07.034
J. A. Curcio and C. C. Petty, “ The near infrared absorption spectrum of liquid water,” J. Opt. Soc. Am. 41( 5), 302- 304 ( 1951). 10.1364/josa.41.000302
S. Siebentritt, U. Rau, S. Gharabeiki, T. P. Weiss, A. Prot, T. Wang, D. Adeleye, M. Drahem, and A. Singh, “ Photoluminescence assessment of materials for solar cell absorbers,” Faraday Discuss. 239, 112 ( 2022). 10.1039/d2fd00057a
S. Sugai, “ Resonant Raman scattering in CuGaS2,” J. Phys. Soc. Jpn. 43( 2), 592- 599 ( 1977). 10.1143/jpsj.43.592
W. Kauschke and M. Cardona, “ Resonant Raman scattering in semiconductors,” Phys. Scr. T25, 201- 205 ( 1989). 10.1088/0031-8949/1989/t25/036
F. Oliva, S. Kretzschmar, D. Colombara, S. Tombolato, C. M. Ruiz, A. Redinger, E. Saucedo, C. Broussillou, T. G. de Monsabert, T. Unold, P. J. Dale, V. Izquierdo-Roca, and A. Pérez-Rodríguez, “ Optical methodology for process monitoring of chalcopyrite photovoltaic technologies: Application to low cost Cu(In,Ga)(S,Se)2 electrodeposition based processes,” Sol. Energy Mater. Sol. Cells 158, 168- 183 ( 2016). 10.1016/j.solmat.2015.12.036
S. Y. Kim, M. S. Mina, J. Lee, and J. H. Kim, “ Sulfur-alloying effects on Cu(in,Ga)(S,Se)2 solar cell fabricated using aqueous spray pyrolysis,” ACS Appl. Mater. Interfaces 11( 49), 45702- 45708 ( 2019). 10.1021/acsami.9b16192
C. Insignares-Cuello, V. Izquierdo-Roca, J. López-García, L. Calvo-Barrio, E. Saucedo, S. Kretzschmar, T. Unold, C. Broussillou, T. Goislard de Monsabert, V. Bermudez, and A. Pérez-Rodríguez, “ Combined Raman scattering/photoluminescence analysis of Cu(In,Ga)Se2 electrodeposited layers,” Sol. Energy 103, 89- 95 ( 2014). 10.1016/j.solener.2014.02.005
D. Nam, J. U. Lee, and H. Cheong, “ Excitation energy dependent Raman spectrum of MoSe2,” Sci. Rep. 5, 17113 ( 2015). 10.1038/srep17113
T. Terasako, Y. Uno, T. Kariya, and S. Shirakata, “ Structural and optical properties of In-rich Cu-In-Se polycrystalline thin films prepared by chemical spray pyrolysis,” Sol. Energy Mater. Sol. Cells 90( 3), 262- 275 ( 2006). 10.1016/j.solmat.2005.03.010
C. Insignares-Cuello, C. Broussillou, V. Bermúdez, E. Saucedo, A. Pérez-Rodríguez, and V. Izquierdo-Roca, “ Raman scattering analysis of electrodeposited Cu(In,Ga)Se2 solar cells: Impact of ordered vacancy compounds on cell efficiency,” Appl. Phys. Lett. 105( 2), 021905 ( 2014). 10.1063/1.4890970
S. B. Zhang, S.-H. Wei, and A. Zunger, “ Stabilization of ternary compounds via ordered arrays of defect pairs,” Phys. Rev. Lett. 78, 4059 ( 1997). 10.1103/physrevlett.78.4059
K. Sato and H. Katayama-Yoshida, AIP Conf. Proc. 1583, 150- 155 ( 2014). 10.1063/1.4865624
K. W. Kazuki Wakita, T. M. Takayuki Miyazaki, Y. K. Yasuhiro Kikuno, S. T. Souichi Takata, and N. Y. Nobuyuki Yamamoto, “ Resonant Raman effect on a CuGaSe2 crystal grown by the traveling heater method,” Jpn. J. Appl. Phys. 38( 2R), 664- 667 ( 1999). 10.1143/jjap.38.664
D. Regesch, L. Gütay, J. K. Larsen, V. Deprédurand, D. Tanaka, Y. Aida, and S. Siebentritt, “ Degradation and passivation of CuInSe2,” Appl. Phys. Lett. 101( 11), 112108 ( 2012). 10.1063/1.4752165
F. Babbe, L. Choubrac, and S. Siebentritt, “ Quasi Fermi level splitting of Cu-rich and Cu-poor Cu(In,Ga)Se2 absorber layers,” Appl. Phys. Lett. 109( 8), 082105 ( 2016). 10.1063/1.4961530
Y. H. Chang, R. Carron, M. Ochoa, C. Bozal-Ginesta, A. N. Tiwari, J. R. Durrant, and L. Steier, “ Insights from transient absorption spectroscopy into electron dynamics along the Ga-gradient in Cu(In,Ga)Se2 solar cells,” Adv. Energy Mater. 11( 8), 2003446 ( 2021). 10.1002/aenm.202003446
S. Niki, R. Suzuki, S. Ishibashi, T. Ohdaira, P. J. Fons, A. Yamada, H. Oyanagi, T. Wada, R. Kimura, and T. Nakada, “ Anion vacancies in CuInSe2,” Thin Solid Films 387, 129- 134 ( 2001). 10.1016/s0040-6090(00)01718-1
L. M. Mansfield, D. Kuciauskas, P. Dippo, J. V. Li, K. Bowers, B. To, C. Dehart, and K. Ramanathan, “ Optoelectronic investigation of Sb-doped Cu(In,Ga)Se2,” IEEE J. Photovoltaics 5( 6), 1769- 1774 ( 2015). 10.1109/jphotov.2015.2470082
S. Siebentritt, A. Lomuscio, D. Adeleye, M. Sood, and A. Dwivedi, “ Sulfide chalcopyrite solar cells-are they the same as selenides with a wider bandgap?,” Phys. Status Solidi RRL 16( 8), 2200126 ( 2022). 10.1002/pssr.202200126
C. Spindler, F. Babbe, M. H. Wolter, F. Ehré, K. Santhosh, P. Hilgert, F. Werner, and S. Siebentritt, “ Electronic defects in Cu(In,Ga)Se2: Towards a comprehensive model,” Phys. Rev. Mater. 3( 9), 090302 ( 2019). 10.1103/physrevmaterials.3.090302
C. Spindler, D. Regesch, and S. Siebentritt, “ Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence,” Appl. Phys. Lett. 109( 3), 032105 ( 2016). 10.1063/1.4959557
