Optical and Electrical Characterisation of P3ht:PCBM Organic Photovoltaic Devices.
TABLE OF CONTENTS
Preface
Dedication………..2
Acknowledgements………3
List of figures…. .6
List of Tables………… 6
1.0 Introduction……….. 8
1.1 Background……..8
1.2 Statement of problem…………9
1.3 Scope of study……..9
2.0 Literature review………..10
2.1 Organic solar cells……10
2.1.1 Photo-excitation in organic solar cells….10
2.1.2 Types of organic solar cells…..10
2.2 PCBM:P3HT………13
2.2.1 Band-gap efficiency………13
2.2.2 Stability………………..14
2.3 Adhesion and charge transport…..15
2.3.1 Adhesion theories…..15
2.3.2 AFM theory and pull off…..16
2.3.3 Adhesion energy modelling and interfacial fracture mechanics.17
2.4 Degradation……….18
2.4.1 Degradation measurements…..20
2.5 Electron and hole transporting layers………..21
2.6 The electrodes……….21
2.7 Thin films……………..22
2.7.1 Sputtering……22
2.7.2 Spin-coating………..23
2.7.3 Thermal Evaporation…..23
3.0 Experimental procedure and discussions……..24
3.1 Mask Fabrication…….24
3.2 Substrate preparation…….25
3.3 Active layer preparation…..25
3.4 Thin film depositions………27
3.4.1 ITO deposition……27
3.4.2 PEDOT:PSS deposition..28
3.4.3 P3HT:PCBM depositions……29
3.4.4 Aluminium depositions……….29
3.4.5 Atomic force microscope preparation………30
3.5 Optical and electrical characterisation……..30
3.5.1 Thickness and roughness determination……..30
3.5.2 Transmittance and absorptance measurements……..31
3.5.3 Sheet resistance determination……32
3.5.4 Electrical characterisation of the device………33
3.6.0 Observations on the various specimen………..35
3.6.1 Devices……35
3.6.2 Semi devices…………46
3.6.3 Further discussions……….50
4.0 Summary, conclusions and recommendations……52
References…….55
INTRODUCTION
1.1 Background
The numerous limitations of inorganic solar cells has led to keen interest and exploitation of organic solar cells in recent times. They offer several advantages such as lightness, mechanical flexibility, low production cost, ease of processing and have a high potential for large area solar conversion1.
The properties, performance and lifespan of these solar cells depend on the properties of the active layer and interface between the components1.
Thus far research efforts have been focused on flexibility, colour for building integration, transparency and tackling some of the challenges limiting the industrial applications of organic solar cells22 especially their low efficiencies.
The efficiency that can be reached with single junction cells is currently in the neighbourhood of 5% while the predictions of the theoretically and practically accessible power conversion efficiencies are predicted to be about twice the value or even higher.
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