Using QPAC® 40 as a Binder in Solar Pastes
A great deal of effort has been afforded over the last 20 years improving photovoltaic (PV) efficiencies, reliability, and manufacturability. Much of this work has been focused on the front-side construction of PV, including metallization and contact formation with glasses. In general, the front-side contact pastes are silver pastes which are heterogeneous mixtures containing metallic silver powder or flakes, glass frit(s), organic binders, and other additives (solvents, plasticizers, dispersant/surfactants, inorganic additives, etc.). The role of the organic binder is critical in the formulation but is many times overlooked.
In this study, the clean burning QPAC 40 Polypropylene carbonate binder was used to formulate a front-side solar cell thick film paste sample. The paste characteristics were compared to commercially available pastes and found to exhibit nearly identical characteristics, such as solids loading, rheology, and fineness of grind. Thermal analysis of the paste sample compared to available commercial systems showed the QPAC 40 based paste to provide complete organic phase burn-out by 300°C in air, whereas the commercial systems exhibited a broad decomposition range and residual carbonaceous material presence as high as 630°C. The final cosmetic and microstructure features of the printed and fired structures on the front-side of solar cells were also compared. The QPAC 40 based paste showed a higher retention of imparted geometry from the screen printing process through narrower and higher finger lines as well as better conductive architecture density through reduction of pore/void features as compared to the commercial paste samples A and B.