Lifetime and encapsulation study of organic solar cells (LEOsc)
Lead Research Organisation:
University of Oxford
Department Name: Oxford Physics
Abstract
The Paris Agreement set the goal to reach Net-Zero emission by 2050 to tackle global warming; this has stimulated much research into energy transition. Photovoltaic technology receives great attention as it can meet increasing energy demands by converting solar radiation into electricity without greenhouse gas emissions. However, global PV deployment is still low (only 5% of global electricity came from PV technology in 2021) and the market is currently dominated by energy-intensive conventional crystalline silicon PV. To facilitate the energy transition, novel photovoltaic technologies, such as organic solar cells (OSCs), are being intensively studied for flexible & lightweight applications. However, OSCs must fulfil requirements in efficiency, lifetime, and cost for future commercialisation. The cost of OSC production and installation is expected to be very low compared to conventional Si. Continuing developments have been made in improving OSC efficiency and indeed competitive high PCE (power conversion efficiency) of about 20% has been reached so far. While OSC lifetime is still substantially lower than that of inorganic cells and there is much room for improvement. Since OSC degradation is mainly caused by exposure to moisture and oxygen, encapsulation of the cells is one of the most straightforward ways to improve OSC life expectancy.
In this context, this Fellowship research focusses on the OSC lifetime study. The proposed tasks involve two aspects, encapsulation layer development and OSC extrinsic degradation mechanism study.
Specifically, the atomic layer deposition (ALD) technique will be utilized for the fabrication of the encapsulation layer. ALD is a technique based on the self-limiting reaction between distinct precursors, which can deposit dense thin films with excellent uniformity. The uniformity of the film allows the water and oxygen permeation rate to be extremely low, thus the encapsulation film can protect OSCs longer. The Fellowship will systematically investigate all the encapsulation strategies by the ALD technique, namely:
(1) Barrier films for lamination. This strategy allows the possibility of manufacturing the barrier films in advance, then OSCs will be laminated with barrier films. A huge advantage of this scheme is the whole processing of a module can be done in a roll-to-roll configuration and the ALD conditions are not limited by the sensitive organics.
(2) Direct thin-film encapsulation (TFE). This strategy is desirable to minimize mechanical stress, abrasion to the barrier, and device contamination. The main issue of TFE is the encapsulation processing conditions are highly constrained by the organics.
In both strategies, OSC encapsulation layers with low moisture permeation and sufficient mechanical durability will be developed, an intermediate layer will also be developed to serve as a better growth surface for ALD materials to ensure the thin films are perfect. The deposition rate will be improved to increase the production throughput of ALD. Comparisons of the encapsulation performance within the different strategies will address the best encapsulation configuration for OSCs. Thereafter, the optimal encapsulation will be utilised for the protection of state-of-the-art OSCs, accelerated tests and outdoor lifetime tests will be performed on the protected OSCs to characterise the lifetime. The extrinsic degradation of encapsulated cells will be also studied to address the cell break-down. Optimisation strategies will be given to the encapsulation layers according to the degradation mechanism. My goal is to push the lifetime of the OSC to a comparable level to that of Si. At the end of the Fellowship, scale-up trials will be undertaken with the help of Oxford Physics' Innovation and Enterprise Manager (Phillip Tait) and our industry partners.
In this context, this Fellowship research focusses on the OSC lifetime study. The proposed tasks involve two aspects, encapsulation layer development and OSC extrinsic degradation mechanism study.
Specifically, the atomic layer deposition (ALD) technique will be utilized for the fabrication of the encapsulation layer. ALD is a technique based on the self-limiting reaction between distinct precursors, which can deposit dense thin films with excellent uniformity. The uniformity of the film allows the water and oxygen permeation rate to be extremely low, thus the encapsulation film can protect OSCs longer. The Fellowship will systematically investigate all the encapsulation strategies by the ALD technique, namely:
(1) Barrier films for lamination. This strategy allows the possibility of manufacturing the barrier films in advance, then OSCs will be laminated with barrier films. A huge advantage of this scheme is the whole processing of a module can be done in a roll-to-roll configuration and the ALD conditions are not limited by the sensitive organics.
(2) Direct thin-film encapsulation (TFE). This strategy is desirable to minimize mechanical stress, abrasion to the barrier, and device contamination. The main issue of TFE is the encapsulation processing conditions are highly constrained by the organics.
In both strategies, OSC encapsulation layers with low moisture permeation and sufficient mechanical durability will be developed, an intermediate layer will also be developed to serve as a better growth surface for ALD materials to ensure the thin films are perfect. The deposition rate will be improved to increase the production throughput of ALD. Comparisons of the encapsulation performance within the different strategies will address the best encapsulation configuration for OSCs. Thereafter, the optimal encapsulation will be utilised for the protection of state-of-the-art OSCs, accelerated tests and outdoor lifetime tests will be performed on the protected OSCs to characterise the lifetime. The extrinsic degradation of encapsulated cells will be also studied to address the cell break-down. Optimisation strategies will be given to the encapsulation layers according to the degradation mechanism. My goal is to push the lifetime of the OSC to a comparable level to that of Si. At the end of the Fellowship, scale-up trials will be undertaken with the help of Oxford Physics' Innovation and Enterprise Manager (Phillip Tait) and our industry partners.
