Investigating photovoltaic performance parameters of organic solar cells under and during 3-point bending flexural testing.
File(s)
Published version
Author(s)
Ahli, Huda
Type
Thesis
Abstract
The overall goal of this thesis was to be able to answer the simple question as to how the performance parameters of a flexible OPV changes as it experiences 3-point mechanical bending tests. An inverted OPV with the structure of (PET/ITO/ZnO/ITIC:PBDP-T/MoOx/Ag) was chosen for this study. Three different bending radiuses were tested, 2.7 cm, 5 cm and 10 cm, and the devices were tested under illumination after 10, 50 and 100 bending cycles. From there, it was noted that bending radiuses of 5 cm and 2.7 cm led to mechanical degradation that resulted in a dramatic drop in Jsc, PCE, along with a dramatic increase in Rs. A novel in-situ method of monitoring the electrical resistance of the device while bending was used, to investigate the effect of bending on the interfaces and the individual layers. Where users will be able to obtain information regarding the mechanical limitation of devices’ interfaces and interlayers for a given bending radius and bending cycles. It was concluded that the resistance overload resulted from a weak interface between MoOx and the active layer, possibly leading to increase in Rs. This was further confirmed via a manual peeling test, indicating that the active layer was intact and the top layer of the peeler had silver and MoO which was reported as a layer underneath the silver, lighter in color. The second mechanical degradation was witnessed in the active layer, as after 100 bending cycles, striation started to appear at 5 cm bending radius, and were more obvious at 2.7 bending radius which could results to further reduction in Jsc due to possible charge recombination processes. An in house, novel system was utilised in this study to understand the behaviour of a flexible OPV under bending, while under illumination with the focus of bending radius of 5 cm. From there, it was noticed that delamination spot changes upon bending and flattening the device causing fluctuations to Rs values and reversible behaviour of the device. Finally, the flexible OPVs were encapsulated via lamination techniques, in an attempt to move the neutral axis towards the device layers and thus, protecting any weak interfaces from mechanical degradation. Although the performance parameters of the flexible OPV, more specifically, Rs and PCE were not degraded with the same severity as the case with un-encapsulated devices. It is believed that the degradation, which is governed by reduction in Voc, FF and Rsh, is resulted from creating a shunting path within the device. Which is believed to be an effect of encapsulation and not mechanical degradation. The FE analysis of both encapsulated and un-encapsulated substrates was conducted clearly indicating movements of the neutral axis towards the mid-plane of encapsulated substrates.
Version
Open Access
Date Issued
2022-03
Date Awarded
2023-02
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
McLachlan, Martyn
Sponsor
United Arab Emirates
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)