Nano-scale patterns such as those found on the exterior surface of eyes of certain nocturnal insects have far-reaching implications in terms of optoelectronic device design. The advantage of these patterns for optoelectronic enhancement in photovoltaic light harvesting is less explored due to the lack of suitable engineered materials to easily fabricate such nanostructures. Team of researchers, A K Jagdish and Gopalkrishna Hegde from Centre for Nano Science & Engineering, Praveen Ramamurthy from Materials Engineering and D R Mahapatra from Aerospace Engineering, have theoretically proved and experimentally demonstrated a novel moldable biomimetic nanoscale optoelectronic platform for simultaneous enhancement in optical absorption and charge transport in organic solar cells.
Here researchers have realized these complex patterns using a self-assembly based molding process on hitherto unexplored robust structural epoxies with excellent repeatability and scalability to larger area. The incorporation of these patterns in the substrate shows nearly a 50% broadband drop in the specular reflectance of the nanostructured substrate. Further, it is demonstrated that by tweaking the bio-inspired patterns on the interior side of a light harvesting device, it is possible to obtain a broadband improvement in the external quantum efficiency in the spectral window between 350 and 650nm leading to a significant improvement of up to 50% in the photocurrent density in the structured devices. From experiment and simulation results, it is observed that this enhancement stems from a combination of two effects – first, a broadband drop in the specular reflectance exceeding 70%, arising from trapped surface plasmon-polariton modes, and – second, an improved charge separation in the structured device arising due to perturbed built-in electric fields. Further, the simulations which take into account the interfacial nano-scale morphology show that for absorbers with low carrier mobilities, a significant improvement in the photocurrent and in the fill factor is simultaneously possible.
Overall this work demonstrates a combination of tweaked biomimetic design and the use of unconventional robust structural materials as nanostructured optoelectronic substrates. This effort can bridge the gap between naturally evolved designs and practical optoelectronics to enhance performance. Further, the simple technique developed will open up a new possibility for fabrication of non-clean room based nanostructured platform for photovoltaic and optoelectronic applications and also large area organic solar cell manufacturing.
The work has been published in the journal Nanoscale(RSC) in Feb.2018. Details are available in the full length paper.