Surface passivation for lead immobilizable perovskite solar cells

다국어 초록 (Multilingual Abstract)

Perovskite solar cells (PSCs) have received great attention due to remarkable optical properties, high absorption coefficient and low cost. Research in this field rapidly developed since first all-solid-state PSCs have been reported by Prof. Nam-Gyu Park. Recently, the PSC devices have certificated over 27% PCE, with great stability including light and thermal. PSC is considered to be the best candidate for next-generation photovoltaic technology. However, stability induced by ionic migration, defects hindering their commercialization. Undercoordinated Pb²⁺ ions located at grain boundaries and surfaces act as traps, accelerating nonradiative recombination and facilitated perovskite decomposition under moisture, heat, or illumination. Moreover, hazardous of lead composition is a critical issue for public’s acceptance of PSC.
In this thesis we have focused surface passivation strategy to achieve the high efficient and lead immobilized PSC devices. Through different functional passivation molecules, including dithiol/dithiolate and phosphonic acid, are systematically investigated. First, we have compared a series of alkane dithiol materials as passivation agents and determined 1,5-pentanedithiol and potassium pentanedithioalte as best candidate. It not only showed a reduced trap density was achieved, but also variation of electrical property of perovskite surface. The passivation results in improved performance and stability, meanwhile a good lead immobilization capacity. Second, we have applied phenyl phosphonic acid (PPA) and benzyl phosphonic acid (BPA), which two materials have similar structure exhibited different passivation effect. Through DFT calculation, we confirmed this phenomenon mainly attributed to the dipole moment caused by intramolecular geometry of two materials. Two passivation agents especially PPA performed outstanding photovoltaic and lead immobilization effect.

국문 초록 (Abstract)

페로브스카이트 태양전지(PSC)는 우수한 광학적 특성, 높은 흡광 계수 및 저비용으로 인해 큰 주목을 받고 있다. 첫 전 고체형 페로브스카이트 태양전지가 보고된 이후, 이 분야의 연구는 빠르게 발전하였다. 그 결과 최근에 27% 이상의 인증된 효율을 달성했으며, 광 및 열 조건에서 우수한 안정성을 보여주었다. 따라서 페로브스카이트 태양전지는 차세대 광발전 기술의 가장 유력한 후보로 여겨지고 있다. 그러나 이온 이동 및 결함으로 인해 발생하는 안정성 문제는 상업화를 저해하고 있다. 특히, 결정경계면와 표면에 존재하는 저배위 Pb²⁺ 이온은 트랩 상태로 작용하여 재결합을 가속화하고, 습기, 열, 빛 조건에서 페로브스카이트 분해를 촉진한다. 또한, 납 성분의 유해성은 태양전지의 독성 문제가 고려해야 한다.
본 논문에서는 고효율 및 납 고정화가 가능한 패로브스카이트 태양전지 제작을 위해 표면 패시베이션 연구에 집중하였다. 이를 위해 dithiol/dithiolate 및 phosphonic acid 기반의 다양한 기능성 패시베이션 분자를 체계적으로 조사하였다. 먼저, alkane dithiol 물질을 패시베이션 믈질로 상용해서 비교하였으며, 그 중 1,5-pentanedithiol 및 potassium pentanedithiolate이 가장 우수한 후보로 확인되었다. 이는 결함 밀도 감소뿐 아니라 페로브스카이트 표면의 전기적 특성 변화도 나타냈다. 이러한 패시베이션은 성능 및 안정성을 향상시키는 동시에 우수한 납 고정화 능력을 제공하였다. 다음으로, 구조가 유사한 phenyl phosphonic acid (PPA)과 benzyl phosphonic acid (BPA)을 적용한 결과, 두 물질은 서로 다른 패시베이션 효과를 보였다. DFT 계산을 통해 이러한 차이는 분자 내부 구조로 인해 형성되는 dipole moment에서 기인함을 확인하였다. 특히 PPA는 뛰어난 광전 성능과 함께 우수한 납 고정화 효과를 나타냈다.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1.1. Global energy issues and climate change 1
• 1.2. Renewable energy 4
• 1.3. Photovoltaic technology and perovskite solar cells 6
• 1.3.1. Semiconductor 6
• 1.3.2. p-n junction 8
• 1.3.3. Photovoltaic effect and solar cells 9
• 1.4 Perovskite solar cells 10
• 1.4.1 Structure of perovskite 10
• 1.4.2 Development of perovskite solar cells 12
• 1.4.3 Issue of perovskite solar cells 16
• 1.5 Characterization of perovskite solar cells 19
• 1.5.1 Characterization of photovoltaic performance 19
• 1.5.2 Characterization of defect behavior 20
• 1.5.3 Characterization of suppress of ion migration 23
• 1.5.4 Lead leakage evaluation 25
• 1.6 Research purpose of thesis 25
• Chapter 2. Interface Engineering via Di-Sulfidation for Enhancing Stability and Lead Immobilization in Perovskite Solar Cells 27
• 2.1 Introduction 27
• 2.2 Experimental approach 32
• 2.3 Passivation effect on photovoltaic property 33
• 2.4 Characterization of interaction between passivation agents and perovskite 38
• 2.5 Characterization of defect behavior 40
• 2.6 Characterization of morphology and electrical property of perovskite 45
• 2.7 Characterization of ion migration and long-term stability 54
• 2.8 Characterization of lead immobilization effect 57
• 2.9 Conclusion 60
• 2.10 Experimental details 61
• Chapter 3. Dual-site Synergistic Surface Passivation with Phenyl Phosphonic Acid for Efficient, Lead-Immobilizable Perovskite Solar Cells 67
• 3.1 Introduction 67
• 3.2 Materials selection 69
• 3.3 Passivation effect on photovoltaic performance 74
• 3.4 Intramolecular geometry effect on photovoltaic performance 80
• 3.5 Characterization of interactions between passivation and perovskite 86
• 3.6 Characterization of passivation effect on morphology and electrical property 92
• 3.7 Characterization of passivation effect on defect behavior 99
• 3.8 Passivation effect on ion migration and long-term stability 107
• 3.9 Passivation effect on lead immobilization capacity 109
• 3.10 Conclusion 111
• 3.11 Experimental details 112
• Summary 120
• References 122
• Appendix 141
• 논문요약 143