Korean scientists led by Jin Young Kim and Soojin Park, both Associate Professors of the Interdisciplinary School of Green Energy at the South Korean Ulsan National Institute of Science and Technology (UNIST) have been working on improving PSC efficiency, which they said must reach at least 10% before the cells become commercially viable.
A polymer solar cell is a type of thin film solar cell 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, but are expensive and complex to produce, raising interest in developing alternative photovoltaic technologies. Compared to silicon-based devices, PSCs are lightweight, important for small autonomous sensors, are potentially disposable due to solution processability, inexpensive to make, flexible, and customisable on the molecular level. They also have a lower potential for negative environmental impact, UNIST says, which is why they have attracted a lot of interest. Their promise of “extremely cheap” production and eventually high efficiency values has made them one of the most popular fields in solar cell research.
Despite these many advantages, PSCs are currently not efficient enough for large-scale applications and often experience stability problems. To maximise power conversion efficiency, light absorption in the active layer must 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. UNIST researchers are therefore exploring ways to minimise the thickness of BHJ films while maximising the light absorption capability in the active layer.
The science
The research team employed what is known as 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,” UNIST says. “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.”
“This is the first report introducing metal NPs between the hole transport layer and active layer for enhancing device performance,” said Professor Kim. “The multipositional and solutions-processable properties of our surface plasmon resonance 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.” Professor Park added: “Our work is meaningful to develop novel metal nanoparticles and almost reach 10% efficiency by using these materials. If we continuously focus on optimising this work, commercialisation of PSCs will be a realization.”
The original research article is available at http://pubs.acs.org/doi/abs/10.1021/nl400730z
Edited by Josie Le Blond