| Reference : OPTICAL ANALYSIS OF EFFICIENCY LIMITATIONS OF CU(IN,GA)SE2 GROWN UNDER COPPER EXCESS |
| Dissertations and theses : Doctoral thesis | |||
| Physical, chemical, mathematical & earth Sciences : Physics | |||
| Physics and Materials Science | |||
| http://hdl.handle.net/10993/38677 | |||
| OPTICAL ANALYSIS OF EFFICIENCY LIMITATIONS OF CU(IN,GA)SE2 GROWN UNDER COPPER EXCESS | |
| English | |
Babbe, Finn  [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit >] | |
| 22-Feb-2019 | |
| University of Luxembourg, Esch-sur-Alzette, Luxembourg | |
| DOCTEUR DE L’UNIVERSITÉ DU LUXEMBOURG EN PHYSIQUE | |
| 159 | |
| Siebentritt, Susanne | |
| Michels, Andreas | |
| Christen, Jürgen | |
| Bücheler, Stephan | |
| Brida, Daniele | |
| [en] Chalcopyrites ; Cu-Rich ; Photoluminescence ; CuInSe2 ; CIGS ; Post depostion treatment ; KF PDT | |
| [en] Solar cells made from the compound semiconductor Cu(In,Ga)Se2 reach efficiencies of
22:9 % and are thus even better than multi crystalline silicon solar cells. All world records are achieved using absorber layers with an overall copper deficient composition, but Cu-rich grown samples have multiple favourable properties. However, especially losses in the open circuit voltage limit the device performance. Within this work these efficiency limitations of chalcopyrites grown with copper excess are investigated. The work has been divided into four chapters addressing different scientific questions. (i) Do alkali treatments improve Cu-rich absorber layers? The alkali treatment, which lead to the recent improvements of the efficiency world record, is adapted to CuInSe2 samples with Cu-rich composition. The treatment leads to an improvement of the VOC which originates roughly equally from an improvement of the bulk and the removal of a defect close to the interface. The treatment also improves the VOC of Cu-poor samples. In both cases, the treatment increases the fill factor (FF) and leads to a reduction of copper content at the surface. (ii) Is the VOC limited by deep defects in Cu-rich Cu(In,Ga)Se2? A deep defect, which likely limits the VOC, is observed in photoluminescence measurements (PL) independent of a surface treatment. The defect level is proposed to originate from the second charge transition of the CuIn antisite defect (CuIn(-1/-2)). During the investigation also a peak at 0:9 eV is detected and attributed to a DA-transition involving a third acceptor situated (135 ± 10) meV above the valence band. The A3 proposed to originate from the indium vacancy (VIn). Furthermore the defect was detected in admittance measurements and in Cu(In,Ga)Se2 samples with low gallium content. (iii) Is the diode factor intrinsically higher in Cu-rich chalcopyrites? Cu-rich solar cells exhibit larger diode ideality factors which reduce the FF. A direct link between the power law exponent from intensity dependent PL measurements of absorbers and the diode factor of devices is derived and verified using Cu-poor Cu(In,Ga)Se2 samples. This optical diode factor is the same in Cu-rich and Cu-poor samples. (iv) Is the quasi Fermi level splitting (qFLs) of Cu-rich Cu(In,Ga)Se2 absorber layers comparable to Cu-poor samples? Measuring the qFLs of passivated Cu-rich and Cu-poor Cu(In,Ga)Se2 samples, on average a 120 meV lower splitting is determined for Cu-rich samples. This difference increases with gallium content and is likely linked to a defect moving deeper into the bandgap, possibly related to the second charge transition of the CuIn antisite defect. Overall, samples with Cu-rich composition are not limited by the diode factor. However, a deep defect band causes recombination lowering the qFLs and thus the VOC. This defect is not removed by alkali treatments. A key component to improve Cu-rich solar cells in the future, especially Cu(In,Ga)Se2, will be to remove or passivate this defect level. | |
| Laboratory for Photovoltaics | |
| Fonds National de la Recherche - FnR | |
| Curi-K and CuRi | |
| Researchers ; Professionals | |
| http://hdl.handle.net/10993/38677 | |
| FnR ; FNR8267152 > Susanne Siebentritt > CURI-K > Cu rich CIS - the effect of potassium treatment > 01/02/2015 > 31/01/2018 > 2014 |
| File(s) associated to this reference | ||||||||||||||
|
Fulltext file(s):
| ||||||||||||||
All documents in ORBilu are protected by a user license.
