Wednesday, 18 Sep 2019

Linköping University develops new method to manufacture organic solar cells

The solar cell modules that have been developed at Linköping University are being developed and manufactured by the spin-off company Epishine

A semi-transparent solar cell module as shown in the photograph with electrodes with two variants of the polymer pedot:pss

8 Feb 2018 | Editor

Researchers at Linköping University, lead by Olle Inganäs, professor and head of a research group has developed a simple method to manufacture printed organic solar cell modules. The results have been published in the scientific journal npj Flexible Electronics.

The researchers said although the power conversion efficiency of organic solar cells are approaching that of conventional silicon solar cells, they don't necessarily have to compete in the same market.

The researchers developed a semi-transparent solar cell module, electrodes with two variants of the polymer PEDOT:PSS (commonly used in organic electronics) are used, where one acts as the anode and the other is modified to become the cathode. What appear as stripes across the solar cell module are lines of either cathode-type or anode-type material. The active layer that absorbs light and produces electrons is located between these electrodes. The individual solar cells are connected in series in the module.

When the electrodes and the active layer are printed as thin films on top of each other, defects in one layer will act as points of attack for the next layer to be printed. These defects reinforce each other and cause short-circuits between the top and bottom. Until now, this problem has been solved by passing a current through the cell.

The researchers have now successfully tested a method in which they use instead the active polymer material as glue.

Two plastic films, one with the anodes and the other with the cathodes, are covered by the active material before the complete unit is laminated together. Since only two layers are to be printed, the number of defects is lower and the probability that two defects are located exactly opposite each other during the lamination is negligible.

The researchers have shown that it is moisture causing the trouble. Small electron traps form in the material that capture electrons before they reach the electrode. The problem can be solved by manufacturing the anode and cathode films, and then rapidly laminating them together with the active polymer in a protective atmosphere. The shorter the period that the film is exposed to moisture the better.

The solar cell modules that have been developed by Olle Inganäs and his group at Linköping University are being developed and manufactured by the spin-off company Epishine, which has chosen to aim at the market for indoor cells.

The solar cells then absorb the indoor illumination and create enough current to power, for example, sensors that keep track of a dog when its owner is not at home, or that measure the indoor humidity or temperature. Indoor illumination has a different spectrum and intensity than sunlight, so the conditions of use are simpler and the efficiency high.

"The organic solar cells can be used in many contexts, not least those in which their special properties are useful: they can be semitransparent, soft, flexible, can be obtained in different colours, and they are cheap to manufacture."

"The defects in each individual cell must be burned away. Not only is this time-consuming, it's not easy to gain access to all cells, and this means that the reject rate for faulty units is quite high."

"It just doesn't happen. But we did discover that when we laminate the two layers together to give a flexible and robust module, the solar cells generate more current when illuminated from one side than from the other. Of course, we want the cell to generate the same current no matter whether the sun is rising or setting."

"We have shown that this lamination method works with many different combinations of polymer, and that the energy efficiency is just as high as that obtained by conventional manufacture."

Olle Inganäs, Pprofessor of biomolecular and organic electronics at Linköping University


Asymmetric photocurrent extraction in semitransparent laminated flexible organic solar cells

Jonas Bergqvist | Thomas Österberg | Armantas Melianas | Luis Ever Aguirre | Zheng Tang | Wanzhu Cai | Zaifei Ma | Martijn Kemerink | Desta Gedefaw | Mats R. Andersson | Olle Inganäs

npj Flexible Electronics | volume 2, Article number: 4 (2018) | doi:10.1038/s41528-017-0017-6

Received: 14 May 2017 | Revised: 26 October 2017 | Accepted: 04 November 2017 | Published online: 05 February 2018


Scalable production methods and low-cost materials with low embodied energy are key to success for organic solar cells. PEDOT(PSS) electrodes meet these criteria and allow for low-cost and all solution-processed solar cells. However, such devices are prone to shunting. In this work we introduce a roll-to-roll lamination method to construct semitransparent solar cells with a PEDOT(PSS) anode and an polyethyleneimine (PEI) modified PEDOT(PSS) cathode. We use the polymer:PCBM active layer coated on the electrodes as the lamination adhesive. Our lamination method efficiently eliminates any shunting. Extended exposure to ambient degrades the laminated devices, which manifests in a significantly reduced photocurrent extraction when the device is illuminated through the anode, despite the fact that the PEDOT(PSS) electrodes are optically equivalent. We show that degradation-induced electron traps lead to increased trap-assisted recombination at the anode side of the device. By limiting the exposure time to ambient during production, degradation is significantly reduced. We show that lamination using the active layer as the adhesive can result in device performance equal to that of conventional sequential coating.

www.liu.se    www.epishine.se   

About Linköping University

Linköping University, LiU, conducts world-leading, boundary-crossing research in fields that include materials science, IT and hearing. In the same spirit, the university offers many innovative educational programmes, frequently with a clear professional focus and leading to qualification as, for example, doctors, teachers, economists and engineers.

LiU was granted university status in 1975 and today has 27,000 students and 4,000 employees. The students are among the most desirable in the labour market and international rankings consistently place LiU as a leading global university.

Source: Linköping University

About Epishine

Epishine is a Swedish greenup that has spun off from Linköping and Chalmers Universities.

Source: Epishine

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