Research: Next-Generation Photovoltaic Technologies

Enhancing low power conversion efficiency in organic photovoltaic cells

Organic photovoltaic (OPV) cells are low-cost, easily processible, and light-weight alternatives to inorganic photovoltaic cells. Low power conversion efficiency (PCE) is one of the key factors that currently hinders commercialization of OPV cells.

Undertaking an integrated approach of synthetic chemistry coupled with studies of both structure and dynamics enables a deeper understanding of organic solar cells, which in turn enables the development of higher efficiency devices.

Argonne scientists are teaming up with scientists at the University of Chicago (led by Prof. Luping Yu) and Northwestern University (led by Prof. Tobin Marks) to tackle the challenge of enhancing PCE in OPVs.  To achieve this goal, the team is targeting each step in the photovoltaic process [link to primer page on PV process]: solar photon harvesting, electron and hole generation and transport, as well as electron/hole collection by the electrodes. Optimizing PCEs for OPV cells is an intricate balancing act, which requires exploration of many factors including structure, energy, and dynamics of fundamental processes of the materials.  The team is currently working on optimizing OPV cells based on composite materials with conducting polymers and fullerene derivatives.  By modifying the polymers using synthetic chemistry, they reduced the bandgap [link to primer page on PV process] to harvest more solar photons than commonly used materials.   Meanwhile, they balanced the low bandgap of the polymers with sufficient driving force to separate the electron and hole created by absorption of the photons.  Using different processing methods, they control the film structure to make it easier for the electron and hole to move through the cell. 

Recently, the team discovered a new class of polymers that were used to fabricate an OPV cell with a record device PCE of >7.4%.  The team was able to demonstrate the source of the high PCE by analyzing the structure of the polymer/fullerene films and the dynamics of electron/hole separation and recombination.

These studies, based in the Argonne-Northwestern Solar Energy Research Center (ANSER), are highly interdisciplinary and synergetic utilizing the state-of-the-art facilities at the Advanced Photon Source for structural characterization, the Center for Nanoscale Materials for dynamics characterization, synthesis at the University of Chicago, and electrode and device fabrication at Northwestern University.

Reference

• J. Phys. Chem. B 114 (2010) 742

March 2010