Electrochemically Self-Assembled ZnO/Rhodamine dye Hybrid 2D-Nanostructure towards One-Pot Synthesis of Solar Cells

We have been exploring new possibilities of electrochemical self-assembly (ESA) of nanostructured ZnO/dye hybrid thin films by cathodic electrodeposition from mixed aqueous solutions of Zn salt and organic dye molecules. The family of rhodamine dyes has been found to yield unique 2D-curtainwall hybrid nanostructures that can be directly employed as a photoactive layer, opening a completely new and extremely simple way to fabricate solar cells out of “one-pot”. Bi-continuous domains of solid rhodamine dye and crystalline ZnO are completely segregated in 20-100 nm scale aligned vertical to the substrate, thus spontaneously resulting in a curtainwall architecture. The volume ratio between ZnO and rhodamine could be varied simply by changing the concentration of dye in the deposition bath. When ZnO/rhodamine volume ratio was about 50/50, such 2D nanostructure could be obtained. Illumination of AM 1.5 simulated sunlight to a solidstate cell employing ZnO/R6G dye layer generated up to 0.42 μA cm of photocurrent and ca. 260 mV of photovoltage. Even though the efficiency was extremely low (up to 0.018%) due to the small photocurrent, the photovoltage action spectrum measured under monochromatic light illumination clearly indicated the contribution from the R6G solid, proving the concept of one-pot synthesized solar cell. While the exciton generated in the R6G solid can effectively diffuse to the ZnO/R6G boundary to generate charge owing to the nearideal nanostructure, the carrier diffusion within the R6G solid seems to be limited. Therefore, further exploration of other organic component having better properties than R6G but still achieving similar nanostructure by ESA will lead us to an extremely simple production of low-cost solar cells. Abstract #2890, Honolulu PRiME 2012, © 2012 The Electrochemical Society