Improved rigid/flexible TCEs by engineering properties and introducing the Novel deposition process for enhancing the performances of the Perovskite solar cells

다국어 초록 (Multilingual Abstract)

Abstracts :

This study includes the improved rigid/flexible transparent conducting electrodes(TCEs) by engineering the properties and introducing the new deposition process for enhancing the performances of the optoelectronic devices. The properties of TCEs, which are determined by materials, structures and deposition process, influence on the performance of the optoelectronic devices, such as solar cells, inorganic/organic light-emitting diodes and touch screen panels. In the text, author engineered the optical properties of the TiO2/Ag/TiO2 multilayers as alternative TCEs for Sn-doped In2O3(ITO) by annealing process. The refractive index of the lower TiO2 layers were controlled by annealing at various temperatures for 1h in air. As a results, as-deposited TiO2/Ag/600 ℃-annealed TiO2 multilayer showed exhibited a high transmittance of 96.6% at 550 nm and yielded the highest Haacke’s figure of merit(FOM) of 193.9 × 10-3 Ω-1. Also, the author introduced the Cylindrical Rotating Magnetron-Sputtering(CRMS) system with high target usage (> 80%) to fabricate large are ITO films (1100 mm × 1300 mm) with high optical transmittance and low sheet resistance, efficiently and cost effectively. Based on data from XRD and HRTEM, author suggested a possible growth mechanism of CRMS-grown ITO films and studied the effects of ITO films thickness on the electrical, optical and surface characteristics of ITO films. In addition, the author introduced the in-line type vertical plasma arc ion plating system to fabricate the flexible of ITO with atomically flat surfaces for high performances flexible perovskite solar cells. Due to the energetic ITO ions accelerated to the substrate led to better optical, electrical, crystallinity, and adhesion than sputtered ITO films. As a results, the flexible perovskite solar cells with ion-plated ITO films showed the better power conversion efficiency(PCE) than the perovskite solar cells with sputtered ITO films. Lastly, author suggested a simple and efficient way to improve the performances of perovskite solar cells by introducing ITO electrodes with a nanoporous surface formed by wet-etching of agglomerated Ag nanoparticles. The perovskite solar cells with optimized nanoporous-surface ITO electrodes showed the high PCE of 20.1 % than perovskite solar cells with flat ITO surfaces (18.3 %).

Conclusion:

In this dissertation includes the improved rigid/flexible TCEs by engineering properties and introducing the novel deposition process for enhancing the performances of the optoelectronic devices.
In Chapter 2, we developed TiO2/Ag/TiO2 multilayer electrodes with high FOM by modifying n of TiO2. n increased with increasing temperature. The 600 ℃-annealed TiO2 multilayer samples exhibited higher transmittance at 550 nm than the as-deposited TiO2 multilayer sample. The 600 ℃-annealed sample exhibited the highest transmittance of 96.8 % at 560 nm, a sheet resistance of 3.31 Ω/sq, and smooth surfaces with an RMS roughness of 1.09 nm. The Haacke's FOM was highest for the 600 ℃-annealed sample. The results indicate that the modification of n could be a potentially important process for fabricating conducting transparent multilayer electrodes for display applications.
In Chapter 3, the electrical, optical, morphological, and structural properties of CRMS-grown ITO were investigated as a function of ITO thickness. We found that the resistivity and optical transmittance of CRMS-grown ITO film is dependent on film thickness. Before reaching critical thickness, the mobility of the CRMS-grown ITO films increased due to the enhanced crystallinity of the (2 0 0) plane; however, the preferred orientation changed from the (2 2 2) plane to the (4 0 0) plane at critical thickness, and the mobility of the CRMS-grown ITO film decreased due to the excessive electron generation and increased electron scattering by (4 0 0) plane. The figure of merit for CRMS-grown ITO films can be divided into the sheet resistance dominant region and average optical transmittance dominant region. Cross-sectional XRD, HREM, and FESEM examinations indicate that CRMS-grown ITO film with increasing film thickness are a promising growth mechanism.
In Chapter 4, we demonstrated the feasibility of using an ion-plated ITO film as a high quality flexible electrode for flexible perovskite solar cells to replace conventional sputtered ITO film. The 100 nm thick ion plated ITO film prepared at room temperature showed a sheet resistance of 15.75 Ohm/sq. a high average optical transmittance of 85.88 % and an inner and outer bending radius of 2 and 5 mm, which are better than sputtered ITO films. Energetic ITO ions accelerated to the substrate led to better crystallinity and adhesion than sputtered ITO films. In addition, the different growth mechanism and absence of resputtering effects during ion plating process resulted in ion-plated ITO films that showed atomically flat and smooth surfaces. Flexible perovskite solar cells fabricated on the ion-plated ITO electrodes showed a higher power conversion efficiency of 16.8 % than sputtered ITO-based perovskite solar cells due to the low sheet resistance and high optical transmittance. This demonstrated that plasma arc ion plating is a promising low temperature and large area coating technique to prepare high quality flexible and transparent ITO electrodes for high performance flexible perovskite solar cells.
In Chapter 5, we demonstrated an efficient and simple process to fabricate ITO electrodes with a nanoporous surface by removing self-agglomerated Ag nanoparticles and Ag atoms from grain boundaries of the crystalline ITO electrode for enhancing the performance of the PSCs. The optimized ITO144/6nm films with nanoporous surfaces had a sheet resistance of 10.17 Ω/sq and an optical transmittance of 89.08 % at 550 nm. From the 2D porous mapping, we found that the porosity of the ITO144/6nm was about 25 %. The increased contact area between ITO144/6nm and the SnO2 layer led to enhancement of the electron extraction efficiency of the PSCs. The PSCs with the ITO144/6nm electrode showed an enhanced PCE of 20.1 %, whereas the PCE of PSCs with reference ITO films was 18.3 %. Because the ITO electrode with a nanoporous surface reduced the contact resistance between the SnO2 layer and the ITO electrodes, the PSCs showed an increased PCE. Based on the performance of the PSCs with an ITO electrode with a nanoporous surface, we demonstrated that the formation of ITO/Ag mixed layer on an ITO electrode and the subsequent etching of Ag is a simple way to fabricate ITO with a nanoporous surface.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1.1 Background of Perovskite Solar Cells(PSCs) 1
• 1.1.1 Structures of Perovskite Solar Cells 1
• 1.1.2 Operating Principle of Perovskite Solar Cells 3
• 1.1.3 Photovoltaic Key Parameters of PSCs 5
• 1.2 Background of Transparent Conducting Electrodes (TCEs) 9
• 1.2.1 Sn-doped In2O3 (ITO) 9
• 1.2.2 Oxide/Metal/Oxide (O/M/O) 10
• 1.3 Novel Deposition System for fabricating Transparent Conducting Electrodes(TCEs) 11
• 1.3.1 Conventional Magnetron Sputtering System 11
• 1.3.2 Cylindrical Rotating Magnetron Sputtering System 12
• 1.3.3 Arc Ion-Plating System 13
• 1.4 Characterization of Transparent Conducting Electrodes (TCEs) 14
• 1.4.1 Optical Properties 14
• 1.4.2 Electrical Properties 16
• 1.4.3 Surface Properties 18
• 1.4.4 Structural Properties 18
• 1.4.5 Mechanical Properties 19
• 1.5 References 32
• Chapter 2. Control of refractive index by annealing to achieve high figure of merit for TiO2/Ag/TiO2 multilayer films 38
• 2.1 Introduction 38
• 2.2 Experimental 41
• 2.2.1 Fabrication of TiO2/Ag/TiO2 multilayer 41
• 2.2.2 Characterization of TiO2/Ag/TiO2 multilayer 41
• 2.3 Results and Discussion 42
• 2.4 Conclusions 47
• 2.5 References 56
• Chapter 3. The effects of film thickness on the electrical, optical, and structural properties of cylindrical, rotating, magnetron-sputtered ITO films 62
• 3.1 Introduction 63
• 3.2 Experimental 64
• 3.2.1 Fabrication of CRMS-grown ITO films 64
• 3.2.2 Characterization of CRMS-grown ITO films 66
• 3.3 Results and Discussion 66
• 3.4 Conclusions 74
• 3.5 References 86
• Chapter 4. Flexible ITO films with atomically flat surfaces for high performance flexible perovskite solar cells 91
• 4.1 Introduction 91
• 4.2 Experimental 94
• 4.2.1 Room temperature coating of ITO films on PET substrate 94
• 4.2.2 Analysis of ion plated flexible ITO films 95
• 4.2.3 Characterization of the flexible perovskite solar cells 96
• 4.2.4 Analysis of the flexible perovskite solar cells 97
• 4.3 Results and Discussion 97
• 4.4 Conclusions 113
• 4.5 Supplementary Information 124
• 4.6 References 128
• Chapter 5. Transparent Sn-doped In2O3 electrodes with a nanoporous surface for enhancing the performance of perovskite solar cells 133
• 5.1 Introduction 134
• 5.2 Experimental 136
• 5.2.1 Deposition of the ITO electrode with self-assembled Ag nanoparticles 136
• 5.2.2 Analysis of the nanoporous ITO electrodes 138
• 5.2.3 Fabrication and analysis of the perovskite solar cells 139
• 5.3 Results and Discussion 140
• 5.4 Conclusions 154
• 5.5 Supplementary Information 169
• 5.6 References 174
• Chapter 6. Conclusions 178
• Publications 181
• Patents 183
• Conference Presentations 183