Characterization and Passivation of Interfaces of Perovskite Films for Enhancing Efficiency and Reliability of Solar Cells
페로브스카이트 태양전지의 효율과 신뢰성 개선을 위한 계면분석 및 페시베이션 연구
- 주제(키워드) Perovskite solar cells , Trap passivation , Interface engineering , Charge extraction , Kelvin probe force microscopy , Buried interface , Device reliability
- 주제(DDC) 547
- 발행기관 아주대학교 일반대학원
- 지도교수 김종현
- 발행년도 2025
- 학위수여년월 2025. 8
- 학위명 박사
- 학과 및 전공 일반대학원 분자과학기술학과
- 실제URI http://www.dcollection.net/handler/ajou/000000035013
- 본문언어 영어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
Perovskite solar cells (PSCs) have attracted immense attention due to their high power conversion efficiencies (PCEs) and potential for low cost, scalable fabrication. However, perovskites are susceptible to the evaporation of volatile species, lattice strain, charge trapping issue due to point defect formation, and ion migration, which can all contribute to the rapid degradation of devices, which remains a critical bottleneck for commercialization. This dissertation presents a systematic study on trap passivation strategies through interface engineering to enhance both efficiency and reliability of PSCs. In this work, approaches to improve the interfaces are introduced via modification of the charge transport layers and perovskite. The properties of modified films and devices are systematically analyzed, and their impacts on the device performance and stabilities are scrutinized. Especially, the electronic traps of the solar cells are deeply investigated throughout the research using optoelectrical analyses. By using these meaningful analysis methods, the correlations between the trap properties and the performance/stability of the device are discussed, and insights on the electronic traps are provided. In Chapter 1, the basics of perovskite solar cells and their component materials are discussed. The device structures and properties of organometal halide perovskites are introduced, and stability issues related to PSCs are addressed. Additionally, the analysis methods to investigate various defects in the perovskite solar cells are introduced with a discussion on the importance of the electronic traps in the bulk and at the interfaces. In Chapter 2, the dynamics of interfacial defects in PSCs were investigated using Kelvin probe force microscopy (KPFM), enabling nanoscale mapping of surface potential variations associated with trap-mediated charge recombination and extraction processes. Under illumination, localized ionic polarization and spatially heterogeneous potential distributions were visualized, indicating the presence of interfacial trap states that act as non-radiative recombination centers. Notably, under low light intensity, where carrier generation is limited, these interfacial traps critically hinder charge collection, amplifying recombination losses. To mitigate such interfacial recombination losses, a dipolar small molecule, bathocuproine (BCP), was introduced. The incorporation of BCP facilitated efficient charge extraction by aligning interfacial energy levels and suppressing trap-assisted recombination. Through KPFM analysis, it was elucidated that BCP promotes trap-free charge transport across the buried interface, thereby revealing the mechanistic role of dipolar molecular interlayers in improving interfacial charge dynamics. In Chapter 3, defect passivation strategies were developed to address the intrinsic instability and trap-mediated losses originating from the buried and exposed interfaces of the perovskite layer. Cesium carbonate (Cs2CO3) was introduced at the SnO2/perovskite buried interface via a sequential engineering approach. This bifunctional modifier simultaneously passivated surface oxygen vacancies on SnO2 and halide-related trap states at the bottom perovskite interface, resulting in enhanced vertical crystallinity, reduced interfacial defects, and improved energy level alignment. The treated interface exhibited more homogeneous charge transport properties and reduced recombination losses, leading to improved device performance and operational stability. Furthermore a comprehensive defect passivation strategy using rubidium iodide (RbI) was developed to address intrinsic instabilities and non-radiative losses across the entire perovskite layer, including the buried interface, bulk, and surface. By introducing RbI into the perovskite precursor, both Rb+ and I⁻ ions were homogeneously distributed throughout the film. These ions preferentially occupied undercoordinated Pb²⁺ sites and halide vacancies, resulting in a significant reduction of trap states at multiple spatial domains. The incorporation of RbI improved perovskite crystallinity, suppressed Pb⁰ formation, and reduced ionic defects and lattice strain. This holistic passivation mechanism led to enhanced optoelectronic properties and thermal-light stability. This study demonstrates that RbI serves as a multifunctional ionic additive capable of facilitating full-depth defect passivation and stabilizing perovskite layers, offering a viable strategy for robust and efficient perovskite solar cells. In Chapter 4, interfacial degradation mechanisms such as redox reactions and proton abstraction at NiOx interfaces were identified as key factors in light-induced instability. To mitigate these reliability degradation pathways, a bilayer interfacial strategy was developed by sequentially introducing trimethylsilyl bromide (TMSBr) and a self-assembled monolayer (SAM) on the NiOx surface. The TMSBr treatment enabled effective passivation of the bottom surface of the perovskite layer and simultaneously promoted the uniform formation of the SAM layer. This dual-functional modification significantly suppressed interfacial redox reactions and associated trap states at the NiOx/perovskite interface, thereby reducing non-radiative recombination under illumination. Devices incorporating this bilayer structure exhibited suppressed hysteresis and enhanced photostability, maintaining stable operation under prolonged light exposure. These findings demonstrate the critical role of buried interface engineering in enhancing the operational reliability of perovskite solar cells. This research provides a multi-scale understanding of interfacial trap states and offers viable passivation strategies that enable PSCs to operate efficiently and stably across various illumination environments. The findings contribute valuable insights into the future commercialization of PSCs for both outdoor and indoor energy harvesting applications.
more목차
Chapter 1. Introduction 1
1.1. Renewable energy landscape and the role of solar photovoltaics 1
1.1.1. Global energy demand and climate change mitigation 1
1.1.2 Solar energy as a key renewable technology 3
1.2 Perovskite solar cells 6
1.2.1 Organic-inorganic hybrid perovskites 6
1.2.2 Device structure and working principle 6
1.3 Performance limits and stability challenges in PSCs 9
1.3.1 Influence of interface defects 10
1.3.2 Mechanism of perovskite degradation 14
Chapter 2. Analysis of Interface Carrier Dynamics : Nanoscale Investigation using SPM 15
2.1 Impact of dipole small molecule on carrier extraction efficiency and carrier dynamics 15
2.2 Introduction 15
2.3 Experimental 17
2.3.1 Materials and devices fabrication 17
2.3.2 Measurements and characterization 17
2.4 Device configuration and indoor photovoltaic characterization 19
2.5 Morphological and interfacial improvement 25
2.6 Charge extraction and surface Trap suppression dynamics characterized by KPFM 26
2.7 Charge transport enhancement and electrical impedance analysis 30
2.8 Conclusions 33
Chapter 3. Enhancing Photovoltaic Performance through Interface Engineering for Passivation 34
3.1 Interface passivation at the SnO₂/perovskite junction using cesium carbonate via an interface engineering approach 34
3.1.1 Introduction 34
3.1.2 Experimental section 36
3.1.2.1 Materials and device fabrication 36
3.1.2.2 Measurement characterization 37
3.1.3 Interfacial modification and electronic structure tuning 38
3.1.4 Investigation of interfacial binding and electronic properties 41
3.1.5 Photovoltaic characteristics 45
3.1.6 Device Performance under various illumination environments 51
3.1.7 Conclusions 57
3.2 Multisite trap passivation in the perovskite bulk and interfaces 58
3.2.1 Introduction 58
3.2.2 Experimental section 61
3.2.2.1 Materials and device fabrication 61
3.2.2.2 Measurement characterization 62
3.2.3 Morphological and optical characteristics 66
3.2.4 Device performance under various illumination environments 69
3.2.5 Comprehensive defect passivation and structural improvements 78
3.2.6 Electronic properties and charge transport enhancement 84
3.2.7 Demonstration of IoT applications using PSC mini-modules 89
3.2.8 Conclusions 92
Chapter 4. Development of Interface Passivation for PSCs Reliable under Light Illumination 93
4.1 Introduction 93
4.2. Experimental section 96
4.2.1 Materials and device fabrication 96
4.2.2 Measurement characterization 96
4.3 Photovoltaic performance under light soaking 98
4.4 Morphology property analysis 101
4.5 Photovoltaic characteristics of perovskite films 107
4.6 Buried interface stability under light stress and degradation pathway analysis 109
4.7. Conclusions 117
Chapter 5. Conclusion 118
References 120
Chapter 1. References 120
Chapter 2. References 123
Chapter 3.1 References 126
Chapter 3.2 References 129
Table 3.2.1 References 134
Chapter 4. References 136
List of Publications 139
List of Presentations 142
List of Patents 144
Korean Abstract (국문 초록) 145
