Stability of Standard and Inverted OPV Devices with the Same Buffer Layers
Paul Dastoor a, Coralie Fenn a, Ben Vaughan a, Xiaojing ZHou a, Warwick Belcher a
a University of Newcastle, Center for Organic Electronics, Faculty of Science and Information Technology, Callaghan NSW 2308, Australia, Australia
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Oral, Coralie Fenn, presentation 100
Publication date: 7th November 2016

As the power conversion efficiency (PCE) of organic photovoltaic (OPV) devices increases beyond 10%, much research interest has gone into understanding the degradation of these devices and improving their stability. The introduction of an inverted device architecture has been credited with improved stability for a number of reasons, including the use of a high work function metal as the top electrode to protect the device from damage by water and oxygen. In order to provide a fair stability comparison, we fabricated devices of both structures using the same interfacial and electrode materials thus removing differences due to material stability. 

We produced OPV devices with standard and inverted structures using zinc oxide (ZnO) as the electron selective layer, molybdenum oxide (MoO3) as the hole selective layer and silver as the top electrode. Unencapsulated devices of each type were then subjected to degradation measurements under either constant or intermittent illuminations conditions for 300 hours after which negligible photovoltaic activity remained. Device characteristics for 6 cells of each type were measured every 30 minutes including open circuit voltage, short circuit current and fill factor. 

The stability of each structure was found to strongly depend on lighting conditions, with the standard structure being more stable under constant illumination and the inverted structure more stable under intermittent illumination. The difference in degradation trends for each structure also suggests that the film deposition order and interfaces play an important role in degradation. 

We also investigated the effect of UV light on the stability of both the inverted and standard structure by performing constant illumination degradation measurements of devices under a UV filter or with the addition of a UV LED. Interestingly, devices of both structures tested under the UV filter degraded much more rapidly than those tested under unaltered constant illumination suggesting UV light plays some part in maintaining device performance. 

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