EAPSI: Fluid Flow-Assisted Assembly of Solar Cell Devices

Valverde Lawrence, Champaign IL

Investigators

Abstract

Organic photovoltaics (OPVs) hold great promise as a solar energy conversion technology which can be easily mass produced and is cheap enough to offer electricity at a price comparable to power generated from traditional coal-fired power plants. Furthermore, the potential for use with flexible substrates opens new opportunities for integration of solar cells with architecture and urban infrastructure. While the advantages of OPVs are attractive, the technology is just emerging from its infancy and has yet to reach power conversion efficiencies exceeding 10%. Most of the critical physics intrinsic to achieving the necessary efficiencies occur in the active layer of a device which is composed of organic polymer semiconductors. This project aims to improve device efficiency by investigating the benefits of controlling the assembly and organization of the active layer at the molecular scale. The research will be conducted under the mentorship of Professor Chih-I Wu at National Taiwan University who has extensive experience with OPVs and similar semiconductor technology and is ideally suited to host this research. Critical processes in the OPV active layer include charge-carrier generation through light absorption and charge-carrier collection due to exciton diffusion, dissociation, and transport to opposite contacts. Excitons?excited, yet still bound pairs of positive and negative charge carriers?in organic materials have relatively low diffusion lengths and mobilities compared to charge transport in typical solid-state photovoltaic semiconductors. As such, the strategy of increasing active layer thickness in order to increase photon interaction with the material leads to lost efficiency due to carrier recombination, often negating the strategy?s intentions. One such solution is to increase effective optical thickness while retaining minimal physical thickness by integration of metallic nanoparticles into the polymer matrix. Solutions such as this, however, are still often deposited by spin-coating, which provides excellent control of active layer thickness, but little control with regard to mesoscale architecture. Recent work at the University of Illinois at Urbana-Champaign has demonstrated enhancement of optoelectronic properties in organic semiconducting polymers due to molecular alignment via microfluidics. This research aims to achieve unprecedented efficiencies through the synthesis of metallic nanoparticle doping with microfluidic directed assembly. This NSF EAPSI award is funded in collaboration with the Ministry of Science and Technology of Taiwan.