Control of interface structures for efficient opto-electronic devices

Abstract

The opto-electronic devices based on conjugated polymers with semi-conducting properties have recently attracted much attention as a promising inorganic counterparts due to their possibility of low-cost fabrication, low-weight, and mechanical flexibility. However, lower devices efficiency comes from low conductivity and non-ohmic contact between organic layers are the obstacles to be commercialized. In this point of view, the control interface structure can be a effective way to solve this problems. In this thesis, efficient opto-electronic devices were fabricated by control of interface structures in various ways. In chapter 2, We modified active layer-metal cathode interface in polymer solar cell by introducing nano-pores. From diffused light spectra, XRD and PL spectrum, it is found that device performance enhancement comes not from charge carrier generation of transportation change but from increased charge carrier collection by enlarging organic-electrode interface area. In chapter 3, We modified active layer-anode interface in polymer solar cell by external light irradiation. We investigate the effect of a UV-irradiated poly(3,4-ethylene dioxythiophene:poly (styrene sulfonate)(PEDOT:PSS) buffer layer on the performance of polymer photovoltaic cells based on poly(3-hexylthiophene)(P3HT) and [6,6]-phenyl-C-61-buytyric acid methyl ester (PCBM) blends. It was found that UV irradiation can reduce the bulk and contact resistance of PEDOT:PSS films, improving the power conversion efficiency due to the lower device series resistance The work function change after UV irradiation and negligible surface morphology change was noticed. In chaper 4, we modified electrolyte-substrate interface in dye-sensitized solar cell(DSSC) by replacing counter electrode and cathode by highly conducting polymer. Due to the low conductivity and catalytic activity, polymer applied DSSC showed poor Jsc and FF values. However, as conductivity of polymer is increased, $J_{sc}$ ...