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This is mostly the work I carried out during my graduate research and the year following my PhD at IISc, Bangalore.
The broad scope of my work here involved investigating novel and scalable paradigms for design and fabrication of optoelectronic materials and devices. The key parameters our group tried to optimize through design were optical transport for enhanced photosensitivity and electro-thermo-mechanical design for enhanced operational lifetime.
Below are some of the specific topics I investigated with a summary of the findings:
Can moldable materials help fabricate biomimetic nanostructures to improve optoelectronic performance?
Can moldable materials help fabricate biomimetic nanostructures to improve optoelectronic performance?
Naturally evolved biological structures provide elegant solutions to efficient light harvesting. A popular example of this is the multiscale array structure on the exterior surface in eyes of some nocturnal insects. However, by optimal design and molded nanofabrication, it is possible to incorporate these structures in the interior thin film photovoltaic devices (solar cells) for simultaneous improvement in optical absorption and charge transport. Additionally, the method developed here opens up pathways for using commercially available structural materials as candidates for flexible nanostructured optical components and platforms. The design explored here leads to measured improvements of nearly 50% in the photocurrent of organic photovoltaic devices based on these biomimetic nanoscale platforms.
Can hierarchical and multiperiodic molded structures offer unconventional solutions in nanophotonic and optoelectronic component design? - Strain-augmented nanomolding for multiscale photonics
Can hierarchical and multiperiodic molded structures offer unconventional solutions in nanophotonic and optoelectronic component design? - Strain-augmented nanomolding for multiscale photonics
Hierarchical structures, both natural and manmade, offer the possibility to design materials with unusual characteristics that are not exhibited by continuum material design. This is possible my introduction of structures at multiple length scales, with each structural scale optimizing a particular function of interest. The overall structured material therefore has the combined functionality arising due to multiple structural features. This research explores the design and fabrication of hierarchical multiperiodic gratings on commercially available epoxies using an unconventional self-assembly based mechanical strain-augmented fabrication process and the subsequent demonstration of such hierarchical structural in optoelectronic design of thin film photodetectors. Specifically, it demonstrates that the structured material platform can simultaneously serve as an optoelectronic substrate and also as an optical filter that can shape the spectrum of the incoming light and therefore the spectral optoelectric response of the photodetector built on it. This opens up pathways for multifunctional integration in the design of photonic and optoelectronic devices and components.
Relevant publications: Advanced Optical Materials 2019, 7, 1900471
The challenge of trapping light within weakly dielectric solar absorbers: the role of metal dielectric nanointerfaces for improved light absorption
The challenge of trapping light within weakly dielectric solar absorbers: the role of metal dielectric nanointerfaces for improved light absorption
Nanoscale structures are imperative for large improvements in optical absorption and higher photocurrents in solar cells. However, the presence of a nanoscale structure alone does not guarantee improved absorption. This problems comes to the fore specially in semiconductor absorbers with weak dielectric behaviour, such as semiconducting polymers. This aspect of my research looked at using theoretical insight from optoelectronic simulations and fabrication of nanoscale organic photovoltaic architectures towards establishing generic design rules for nanoscale photovoltaic design specially involving weakly dielectric semiconductors. We find that it is imperative to have both nanoscale dielectric optical entry interfaces and metallic nanointerfaces at the rear of the device for effective light trapping in photovoltaics with weakly dielectric absorbers.
Can we build failure resistant soft-electronics by understanding coupled thermo-electro-mechanical processes dictating failure of organic electronic devices?
Can we build failure resistant soft-electronics by understanding coupled thermo-electro-mechanical processes dictating failure of organic electronic devices?
Soft electronic devices comprising polymeric active layers are often susceptible to catastrophic in-operation failure. Probing these failure mechanisms leads to unraveling an interesting interplay between thermal, mechanical, and electrical processes that lead to distinct chain-like pattern of defects which specifically nucleate at joule-effect driven hot-spots. The opposing stresses due to thermal and electric fields lead to two distinct types of defects that eventually spread across the device and destroy it, springing from mutually exclusive failure criteria for the metal electrodes and the active polymer layers. While understanding these processes helps build failure-tolerant device designs, it also throws light on the intriguing coupled effects at the heart of many processes of practical importance.
Relevant publications: Organic Electronics, Volume 39, 2016, Pages 354-360, Proceedings Volume 9360, Organic Photonic Materials and Devices XVII; 93600S (2015)
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