In this thesis, the modified grating solar cells with porous silicon structure were fabricated by electrochemical etching (ECE). The morphology of the macropores was examined by the SEM analysis. The effects of HNO3 treatment and post oxidation annealing (POA) were investigated. The passivation techniques with TEOS and Al2O3 were also studied. The electrical properties of the modified grating solar cells were characterized through the dark and photo current-voltage (I-V) measurements.
The HNO3 treatment incorporated POA show positive effects on the Jsc improvement. The Jsc can achieve 36 ~ 38 mA/cm2. The devices with sputtered Al2O3 film show a little Voc improvement. By introduced the SiNx hard mask process (SMP), the Voc enhances to 0.54V and 0.58V, the maximal F. F. can reach 0.61 and 0.72 for high – ρ and low – ρ devices, respectively.

Contents
List of Tables
List of Figures
Chapter 1 Introduction ………………………………………1
1.1 Background and Motivation ……………………………….1
1.2 Solar cell………………………………..…………………..3
1.2.1 Basics and types of solar cell…………………………………3
1.2.2 The Physical of the solar cell……………………….………...7
Chapter 2 Solar Cell Operation………………..…………....10
2.1 The Current and Voltage Characteristic…………………..10
2.2 Short Circuit Current …………...………………………...12
2.3 Open Circuit Voltage…………………..………………….13
2.4 Fill Factor………………………………………………….14
2.5 Efficiency………………………………………………….15
2.6 Electrical Losses…………………………………………..16
Chapter 3 Experimental process and techniques…………..18
3.1 Fabrication Processes….…………………………………..18
3.1.1 Process flow chart……………………………………………18
3.1.2 Formation of Porous Silicon layer…………………………...20
3.1.3 Process flow of device……………………………………….22
3.1.4 Tuning parameters of processes……………………………...23
3.2 Techniques of measurement……………………………….25
3.2.1 Scanning Electron Microscope (SEM)……………………….25
3.2.2 Spreading Resistance Probe System (SRP)…………………..28
3.2.3 Solar simulator………………………………………………..29
Chapter 4 Physical characterization………………………..31
4.1 SEM characterization SEM characterization……………...31
4.1.1 Grating structures…………………………………………….31
4.1.2 POCl3 , top metal, SiNx, and TEOS identification…………...40
4.2 SRP characterization………………………………………45
4.2.1 POCl3 doping profile and concentration……………………..45
Chapter 5 Electrical characterization………………………46
5.1 Photo current-voltage analysis…………………………….48
5.1.1 Effects of thermal oxidation and HNO3 treatment…………...48
5.1.2 Effect of post HNO3 oxidation annealing (POA)……………49
5.1.3 Effect of passivation…………………………………………52
5.1.4 Effect of post SiNx deposition annealing…………………….56
5.1.5 Effect of using SiNx hard mask………………………………57
5.2 External quantum efficiency (EQE) characteristics….........61
5.3 Temperature correction……………………………………63
Chapter 6 Conclusions and Future work.………………….66
References……………………………………………….……68

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