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Organic solar cells

Thomas Bein receives ERC Advanced Grant

Munich, 01/15/2013

LMU chemist Professor Thomas Bein has received an Advanced Grant worth some 2.5 million euros from the European Research Council to enable him and his colleagues to study ordered chemical systems as models for more efficient solar cells. ERC Advanced Grants are intended for European researchers who have already made outstanding contributions to their fields, and are designed to give them the freedom to tackle particularly challenging and highly innovative projects.

The sun supplies us with a superfluity of energy, and we have learned ways of harnessing it, in particular by means of silicon-based solar cells. However, in the face of ever-rising production costs and the high energy input required to manufacture them, researchers all over the world are feverishly searching for better alternatives. Organic solar cells represent one potential solution. The ideal solar cell should offer high conversion efficiency, and be easy to fabricate using starting materials that are cheap and widely available - ideally from renewable sources.  Pigmented polymers, low-molecular-weight dye molecules and inorganic nanoparticles meet some of these criteria, and all these systems are currently under intensive study.

Squeezing more energy from sunlight
When a quantum of light – a photon – strikes a molecule in a solar cell it raises one of the outermost electrons onto a higher energy level, creating a so-called “hole” (essentially a localized positive charge). If the energetic electron can be passed on to neighboring acceptor molecules, losing energy as it goes, the result is a tiny electric current. However, if the electron simply falls back to its initial energy level, the energy imparted by the photon is given off as heat. Organic solar cells consist of an ordered mixture of so-called acceptor and donor molecules. Electron acceptors are responsible for electron transport, while the donors serve as an electron source that fills up the holes. However, researchers have hitherto had little control over the precise spatial relationship between donors and acceptors in solar cells.

The proposal submitted to the ERC by LMU chemist Professor Thomas Bein, entitled “Electroactive Donor-Acceptor Covalent Organic Frameworks (ECOF)",  is devoted to changing this state of affairs. Bein, who is also a member of the Nanosystems Initiative Munich (NIM), and his colleagues plan to develop materials in which the donor and acceptor molecules can be arranged in ordered spatial networks by means of directed activation of specific functional groups.

The aim is to design a synthetic route that allows one to define the most important features of the end product - its electronic characteristics, the ordering of donors and acceptors or the thickness of the material - at the outset. So-called Covalent Organic Frameworks (COFs), highly porous molecular networks that can be synthesized from heteroaromatic molecules, provide the basis for this approach.

“I am particularly pleased that we will be able to collaborate with the groups led by Professors Paul Knochel and Dirk Trauner , both based in the Department of Chemistry. Together we will incorporate new organic monomers into donor-acceptor networks and characterize their physical properties", says Bein who intends to grow the networks as honeycomb-like grids on an thin wafers, so that they can be easily integrated into solar cells.

Professor Thomas Bein studied Chemistry at the University of Hamburg and performed his doctoral work at the Catholic University of Louvain (Belgium) and at Hamburg University from 1981 until 1984. He subsequently worked for DuPont Central Research in Wilmington, Delaware (USA) before moving to the University of New Mexico in Santa Fe (USA). In 1991 Bein became an Associate Professor at Purdue University in Lafayette, Indiana (USA), and was later appointed as Full Professor of Chemistry there. Since 1999 Bein is head of the Institute of Physical Chemistry II in the Department of Chemistry at LMU Munich, and has been a member of the Nanosystems Initiative Munich (NIM), a Cluster of Excellence, since its inception in 2006.

ERC Advanced Investigator Grants
ERC Advanced Investigator Grants are designed to support highly innovative research, which has the potential to extend significantly the frontiers of existing fields and pioneer the investigation of new areas. Projects are assessed solely on the basis of the scientific stature of their authors and the originality and quality of the proposed research program.

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