Sep 19 2014
University of Massachusetts, Amherst researchers have designed a light-weight, highly efficient and easily processable solar cell that can use almost any metal as the electrode, successfully impairing the so-called ‘electrode barrier’.
The disadvantages of coventional metallic electrodes, especially their oxidative instability, have been a major obstruction for improving the power conversion efficiency of solar cells.
Todd Emrick, polymer science professor and synthetic chemist, and doctoral student in polymer chemistry, Zak Page were synthesizing novel polymers having zwitterions on them and applying these to varied polymer scaffolds in conjugated systems, called semiconductors, in the solar cell interlayer.
The researchers discovered that zwitterions are neutral having both a negative and a positive charge and also feature powerful dipoles, which interact with metal electrodes. As a result of continued research, Page succeeded in synthesizing conjugated polymer zwitterions or CPZs. The researchers then began working on how to use the CPZs to alter the work function of various metals.
Under the guidance of Photovoltaic facility director of UMass, Amherst, Volodimyr Duzhko in the use of ultraviolet photoelectron spectroscopy (UPS), Page started categorizing a number of metals including gold, silver and copper to find out what helped transport of electrons from the photoactive layer to the electrode. They discovered that in order to enhance interlayer characteristics, the interface layer must be below 5nm, which is a manufacturing challenge.
Hence the scientists considered fullerenes or buckyballs, which are mostly used in the solar cell photoactive layer. Buckyballs were modified using zwitterions (C60-SB) to alter the electrode work function and they were able to easily integrate zwitterions functionality into a fullerene, effectively in three simple steps since they already had experience with polymers.
Subsequent tests suggested that C60-N fullerene layer worked more effectively when compared to the C60-SB type. It was found that a thin C60-N layer between the photoactive layer and the electrode of the solar cell was the most efficient and there was no need for it to be ultra-thin.
The researchers, thus succeeded in creating fullerenes and polymers that alter the properties of the metals they contact transforming them into more efficient devices.