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Polymer solar cell boasts 8.92% conversion efficiency

Posted: 08 May 2013 ?? ?Print Version ?Bookmark and Share

Keywords:polymer solar cell? metal nanoparticle? plasmonic?

A team of researchers from Ulsan National Institute of Science and Technology (UNIST) has demonstrated high-performance polymer solar cells (PSCs) with 8.92 per cent power conversion efficiency (PCE). According to them, the PCE of the solar cells is the highest to date for plasmonic PSCs using metal nanoparticles (NPs).

A polymer solar cell is a type of thin film solar cells made with polymers that produce electricity from sunlight by the photovoltaic effect. Most current commercial solar cells are made from a highly purified silicon crystal. The high cost of these silicon solar cells and their complex production process has generated interest in developing alternative photovoltaic technologies.

Compared to silicon-based devices, PSCs are lightweight (which is important for small autonomous sensors), solution processability (potentially disposable), inexpensive to fabricate (sometimes using printed electronics), flexible and customisable on the molecular level, and they have lower potential for negative environmental impact. Polymer solar cells have attracted a lot of interest due to these many advantages.

Polymer solar cell

(a)Device structures, (b)J-V characteristics, and (c)EQE of PTB7:PC70BM-based PSCs with type I and type II architectures.Copyright : UNIST

Despite these advantages, PSCs suffer from a lack of enough efficiency for large scale applications and stability problems but their promise of extremely cheap production and eventually high efficiency values has led them to be one of the most popular fields in solar cell research.

To maximise PCE, light absorption in the active layer has to be increased using thick bulk heterojunction (BHJ) films. However, the thickness of the active layer is limited by the low carrier mobilities of BHJ materials. Therefore, it is necessary to find the ways to minimise the thickness of BHJ films while maximising the light absorption capability in the active layer.

The research team used the surface plasmon resonance (SPR) effect via multi-positional silica-coated silver NPs (Ag@SiO2) to increase light absorption. The silica shell in Ag@SiO2 preserves the SPR effect of the Ag NPs by preventing oxidation of the Ag core under ambient conditions and also eliminates the concern about exciton quenching by avoiding direct contact between Ag cores and the active layer. The multi-positional property refers to the ability of Ag@SiO2 NPs to be introduced at both ITO/PEDOT:PSS (type I) and PEDOT:PSS/active layer (type II) interfaces in polymer: fullerene-based BHJ PSCs due to the silica shells.

Because PSCs have many advantages, including low cost, solution processability and mechanical flexibility, PSCs can be adopted in various applications. However, we should break the efficiency barrier of 10 per cent for commercialisation of PSCs.

Jin Young Kim and Soojin Park, both, associate professors of the Interdisciplinary School of Green Energy, Ulsan National Institute of Science and Technology (UNIST), Ulsan, South Korea, led this work.

Kim said, "This is the first report introducing metal NPs between the hole transport layer and active layer for enhancing device performance. The multi-positional and solutions-processable properties of our surface plasmon resonance (SPR) materials offer the possibility to use multiple plasmonic effects by introducing various metal nanoparticles into different spatial location for high-performance optoelectronic device via mass production techniques."

"Our work is meaningful to develop novel metal nanoparticles and almost reach 10 per cent efficiency by using these materials. If we continuously focus on optimising this work, commercialisation of PSCs will be a realisation but not dream," added Park.

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