1

PHOTOELECTROCHEMISTRY

2

Photoelectrochemistry/Solar cells

Introduction

Semiconductor–Electrolyte interface

• energy band structure near the interface

• Photo-assisted reaction

Photoelectrochemistry and Solar cells

• photoelectrochemical cells

• Solar cells (photovoltaic cells)

3

Photoelectrochemistry: Introduction

1. Definition and application

2. Semiconductor

Photoelectrochemistry

: conversion of energy between light and electric or chemical energy

: solar cells (light energy → electric energy)

: photoelectrolysis cells, photocatalystic cells

(light energy → chemical reaction, ex: electrolysis of water, detoxificaton)

: semiconductor electrode-electrolyte interface

Semiconductor

: energy band gap Eg<~3eV

: electron and hole carry charge, which can be generated by thermal excitation, photo-excitation (hν>Eg), doping of impurities (p-type / n-type)

4

Semiconductor-electrolyte interface

1. Energy band bending

2. Under irradiation

Exchange of charge between electrode and electrolyte

: may occur depending on the position of EF and the oxidation/reduction energy level

: this forms a space charge region inside the semiconductor electrode

→ bending of energy band

: electrolyte double layer is formed near the interface in the electrolyte region

Thickness of space charge region

- metal: very thin (~Å, due to free electrons)

- semiconductor: relatively thick (nm~μm, because concentration of charge carrier is small)

With irradiation of photon whose energy > Eg

: e-h pair generation

: generation of current due to the bending of energy band

(photoanodic current)

5

* 전기화학 (오승모 저)

6

* 전기화학 (오승모 저)

7

* 전기화학 (오승모 저)

8

Photoelectrochemistry and Solar cells

1. Photoelectrochmical cells

2. Solar cells

Photoelectrochemical cells

: composed of semiconductor electrode, counter electrode, and electrolyte

: photo energy → electric or chemical energy

: Ex) photoelectrolysis of water (photoelectrolytic cell)

2H2O → O2+4H++4e-

4H+ + 4e- → 2H2

: 2H2O → 2H2+O2

: the reaction is driven by photon energy

: hydrogen, oxygen and electric current can be obtained

: photocatalyst bases on the same mechanism

Solar cell (photovoltaic cell)

: photon energy → e-h pair → electron flow(electrode)

/ oxidation(electrolyte) → current → reduction (electrolyte)

: dye is used to absorb wide range of wavelength of light

(dye-sensitized solar cell)

cf) P-N junction solar cells (solid state solar cell)

: e-h pair generation by photo energy → flow of them by the energy band structure

9

* 재료전기화학 (이철태 저)

10

* 재료전기화학 (이철태 저)

11

* 전기화학 (오승모 저)

12

* 재료전기화학 (이철태 저)

13

* 전기화학 (오승모 저)

14

* 전기화학 (오승모 저)