Optical description of solid-state dye-sensitized solar cells. I. Measurement of layer optical properties

Adam J. Moulé,Markus Kaiser,Henry J. Snaith,Klaus Meerholz,Heike Klesper,David M. Huang,Michael Grätzel

doi:10.1063/1.3204982

Abstract

The efficiency of a photovoltaic device is limited by the portion of solar energy that can be captured. We discuss how to measure the optical properties of the various layers in solid-state dye-sensitized solar cells (SDSC). We use spectroscopic ellipsometry to determine the complex refractive index of each of the various layers in a SDSC. Each of the ellipsometry fits is used to calculate a transmission spectrum that is compared to a measured transmission spectrum. The complexities of pore filling on the fitting of the ellipsometric data are discussed. Scanning electron microscopy and energy dispersive x-ray spectroscopy is shown to be an effective method for determining pore filling in SDSC layers. Accurate effective medium optical constants for each layer are presented and the material limits under which these optical constants can be used are discussed.

Highlights

Dye-sensitized solar cellsDSCsoffer a low-cost alternative to traditional crystalline photovoltaic devices.[1]
In this and the subsequent articleParts I and II, respectively, we report on the measurement of the complex refractive index of the various layers in a SDSC and optical modeling of completed devices
In Part I, we focus on accurately determining the complex refractive indexn␭͒ + ik␭͔͒ of each of the device layers. n␭͒ + ik␭͒ is determined using spectroscopic ellipsometry in reflection mode and verified using UV/vis spectroscopy in transmission mode

Summary

INTRODUCTION

Dye-sensitized solar cellsDSCsoffer a low-cost alternative to traditional crystalline photovoltaic devices.[1]. Though the electrical function of the SDSC has been studied using a variety of methods,[10,11,12] it is not clear to what extent the EQE is limited by light absorbance and what percentage of the absorbed light is eventually lost through other channels. In this and the subsequent articleParts I and II, respectively, we report on the measurement of the complex refractive index of the various layers in a SDSC and optical modeling of completed devices. The implications for improved device efficiency are discussed in Part II.[13]

EXPERIMENTAL

Ellipsometry of a single interface

Optical properties of individual layers

A Lorentzian oscillator has the general form

Optical properties of mixed multilayers

CONCLUSIONS