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Date: 22-10-13

Organic solar cell efficiency boosted by researchers at UNIST

The polymer/organic solar photovoltaic cells are preferred for their properties of lightness, flexibility, easy to manufacture and low-cost. The challenge for the researchers in organic solar cell is achieving higher efficiencies. There is continuous research going on to rise the efficiency levels of organic solar PV cells. Achieving the efficiency of 10% is good enough to make them commercially viable.

Korea-based UNIST research team have developed an amine based polar solvent treatment, which enhances the efficiency of inverted polymer solar cells (iPSC). Authors of this research have published their work in the leading science journal, the Advanced Materials.

ORGANIC SOLAR PV

The release from the University has given the below explanation of this technology:
Inverted organic solar cell (IOSCs) that are based on bulkheterojuction (BHJ) is highly attractive materials due to much better air-stability using metal oxides (ZnO, TiOx, and etc.) as buffer layers and high WF metals (Ag or Au) as top electrodes.

In an inverted cell, the electric charges exit the device in the opposite direction as in a normal device. This happens because the positive and negative electrodes (which absorb the negative and positive charges, respectively) are reversed. Inverting the device architecture has the advantage of long-term stability because the electrode compositions are robust to both oxygen and humidity

In spite of the many advantages of iPSCs, device performance given in terms of short circuit current, fill factor, and power convergence efficiency is not very high due to the large contact barrier between the active layer and the electrodes.

The UNIST research team demonstrated highly efficient iPSCs using a simple surface treatment using a polar solvent, which tunes the barrier between the lowest unoccupied molecular orbital (LUMO) of the ZnO-R and active layer, and results in improved device performance.

“We made a remarkable enhancement of iPSC efficiency by reduction of the energy barrier between the conduction band (CB) of ZnO and the LUMO of the acceptor in an active layer,” said Prof. Song.

The high efficiency of the iPSCs originates from interfacial dipolar polarization, which comes spontaneously from the absorption of the ethanolamine (EA) end group. The EA interfacial dipole layer including amine groups creates an ohmic contact, leading to improved electron mobility, suppresses bimolecular recombination, and reduces the contact resistance and series resistance.

Fellow researchers include Bo Ram Lee, Eui Dae Jung Yun Seok Nam, Prof. Jin Young Kim and Hyung-Joon Shin from UNIST, and Prof. Shinuk Cho from the University of Ulsan.

This work was supported by Korea Institute of Materials Science (KIMS) and the National Research Foundation of Korea by the Ministry of Science, IC & Future Planning.

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