Thin Film Solar Cells Using ZnO Nanowires, Organic Semiconductors and Quantum Dots

Abstract

The abstract and thesis of Kaitlyn V anSant for the Master of Science in Physics were presented May 11, 2007, and accepted by the thesis committee and the department. A thin film organic/ inorganic hybrid solar cell was fabricated by incorporating ZnO nanowires, n-and p-type organic semiconductors and inorganic quantum dots.The basic cell design involved the electrodeposition of ZnO nanowires grown on a substrate coated with a transparent conductive oxide. The ZnO nanowires were coated with a thin layer of an organic n-type material, followed by a deposition of inorganic quantum dots. A p-type polymer layer was subsequently deposited and the sample was then contacted with gold to form a quantum dot layer sandwiched between a p-n junction of organic conductive materials.Various materials and processing methods were adjusted, using I-V characteristics, photovoltage and/ or photocurrent measurements to determine the performance of the cell. Each constituent material in the basic device design was evaluated in terms of its contribution to the sample characteristics. A variety of deposition techniques were investigated to obtain homogeneous layers. Different 2 annealing procedures were explored with· the intent of balancing the time and tem:peratures required for electrical activation with material constraints such · as tendency towards oxidat~on and low meltiJ?.g points. The effect of time on the sample characteristics was also observed. The evaluatiOn primarily includes data for samples that led to design modifications aimed at improving both electrical properties and quantum efficiencies.This research led to the development of a hybrid solar cell sensitized by the addition of quantum dots. The organic semiconductors were used to form a p-n junction, and the p-type polymer also served as an active absorber layer. The quantum dots were used as the inorganic absorber fayer, and the results show that the range of optical absorption in the cell can be modified by adjusting particle size. In addition, the ZnO nanowires appear to improve charge transfer, when used with materials that have favorable band offsets.