Identifying parasitic current pathways in CIGS solar cells by modelling dark JV response

Abstract

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. ABSTRACTThe non-uniform presence of shunting defects is a significant cause of poor reproducibility across large-area solar cells, or from batch-to-batch for small area cells, but the most commonly used value for shunt parameterisation (the shunt resistance) fails to identify the cause for shunting. Here, the use of equivalent circuit models to describe dark current-voltage characteristics of ZnO:Al/i-ZnO/CdS/CIGS/Mo devices in order to understand shunting behaviour is evaluated. Simple models, with a single shunt pathway, were tested but failed to fit experimental data, whereas a more sophisticated model developed here, which includes three shunting pathways, yielded excellent agreement throughout the temperature range of 183-323 K. The temperature dependence of fitting parameters is consistent with known physical models. Activation energies and contact barriers are determined from the model, and extracted diode factors are unique across the voltage range. A case study is presented whereby the model is used to diagnose poor reproducibility for CIGS devices (efficiency~3-14% across a 100 cm 2 plate). It's shown that lower efficiencies correlated with greater prevalence of Ohmic and non-Ohmic shunt currents, which may form due to pinholes in absorber and buffer layers respectively, whereas the quality of the main junction was constant for all cells (diode factor~1.5-2). Electron microscopy confirmed the presence of ZnO:Al/i-ZnO/Mo and ZnO:Al/CIGS/Mo regions, supporting the mult...

The role of nanoparticle inks in determining the performance of solution processed Cu2ZnSn(S,Se)4 thin film solar cells

“…Analysis of Figure reveals that the prolonged reaction time results in a selenized thin film that has slightly larger grains (Figure (d)) compared with the hot reaction condition (Figure (c)). This reduces the number of grain boundaries and, in turn, the number of shunt pathways and is evidenced by the higher R SH value.…”

High Voc upon KF Post-Deposition Treatment for Ultrathin Single-Stage Coevaporated Cu(In, Ga)Se2 Solar Cells

“…Non-ohmic shunts can have several origins, of which tunneling at the CdS/CIGS interface due to high concentration of deep defects and shunts along grain boundaries are the most likely candidates. 50 Since it is more severe under blue light and related to the KF treatment, we think it comes from tunneling at CdS/CIGS junction. Similar results are obtained for the covered cells as well.…”

The competing roles of i-ZnO in Cu(In,Ga)Se2 solar cells

“…The (400 nm thick) Mo layer was generated by DC sputtering, the CIGS (1.5 mm) by co-evaporation (Ga/(Ga þIn) ¼ 0.3), the CdS (80 nm) by chemical bath deposition, the i-ZnO (60 nm) by either thermal-ALD or RF sputtering (see below), and the ZnO:Al (200 nm, resistivity, ρ¼5 Á 10 À 4 Ω cm, and sheet resistance, R sheet ¼25 Ω/□) by RF sputtering at room temperature. This fabrication process is the same as has been reported before [8], besides the introduction of ALD i-ZnO. All cells reported here were completed by evaporation of Ni/Ag/Ni finger contacts, and defined by scribing into individual cells (5 mm  10 mm).…”

“…Throughout this manuscript, comparisons are primarily made between the best cells (upper quarters of data sets) in order to focus on the effect of the i-ZnO on the obtainable performance, and to exclude the influence of heavily shunted cells (the prevalence of which is discussed in Section 3.3), which are a result of randomly distributed CIGS defects (see Ref. [8]) -Cu-spitting during co-evaporation results in the formation and fall-off of CuSe x particles. The spatial distribution of these across a 10 cm  10 cm sample appears to be random, and consecutive CIGS depositions show a negligible variation in the extent of Cu-spitting, but over the time scale of months, the prevalence can vary.…”

“…And yet, despite its ubiquity, there is a distinct shortage of understanding regarding exact role of the i-ZnO. In general, it is usually thought that the resistive i-ZnO acts only to minimise the detrimental effect of short-circuit pathways and weak diodes, which may develop in the presence of pinholes in the CIGS or buffer layers [8], thereby increasing the shunt resistance, fill factor (FF) and open-circuit voltage (V oc ). This particular effect has been shown by several research groups [9][10][11].…”