Biodegradable polymer solar cells

Polymer photovoltaic devices were prepared using a biodegradable poly-l-lactic acid (PLLA) substrate loaded with nanoclay in an attempt to improve the thermal properties and possibly reduce permeation of water and oxygen. The nanoclay-loaded PLLA substrates were prepared by compounding and extrusion. The substrate thickness was 200 μm and the substrates had good transparency in the range 300–800 nm of, respectively, >80% for PLA and >60% for PLLA loaded with nanoclay. Devices were realized by application of a conducting transparent anode comprising an aluminium grid with a thin overlayer of silver and spin-coated PEDOT:PSS. The active layer consisted of microfibrillar P3HT and PCBM to encompass the low processing temperatures for PLLA and finally an evaporated aluminium cathode. It was found that PLLA as a substrate holds potential, but there are several challenges beyond the photovoltaic itself which must be met before general application within this field can be envisaged. The most important aspects are the planarity of the PLLA surface, the mechanical stresses induced by the extrusion process, the limitation in processing temperature, and the limitation in the available range of solvents for solution processing.