Rational Design of Passivation Layer for Efficient and Stable 2D/3D hybrid perovskite solar cell

DoctorChemical stability of perovskite determines the device lifetime of perovskite solar cells (PSC). Since surface of perovskite is terminated with under-coordinated ions, it is highly reactive to external stress such as light, oxygen and moisture, facilitating degradation of perovskite material and consequently leading to lower charge collection efficiency. Therefore, it is essential to passivate surface and grain boundary of perovskite thin film to achieve long term operation lifetime, which is prerequisite for commercial deployment. Many previous researches have introduced various kind of molecular additives to stabilize the surface of perovskite film. Among them, particular kind of passivation layers called 2D perovskites have shown successful to enhance both power conversion efficiency and operation stability. However, the role and the effect of structural characteristics of 2D perovskite on the optoelectrical property and device lifetime of PSC remains unclear. Herein, this thesis is dedicated to the systematic understanding and development of rational design principle of 2D perovskite structure and the realization of efficient and long term stable PSC based on novel 2D perovskite. In Chapter 2, the effect of structural arrangement of PbI6 inorganic slab on the crystal formation of α-FAPbI3 perovskite and on the optoelectrical properties of PSCs are elucidated. We discovered that the connection angle of Pb-I-Pb (equitorial) in the LD perovskite changes the rate of α-FAPbI3 formation. Facilitated nucleation of α-FAPbI3 at the optimized FAPbI3/LD interface resulted in minimal structural disorder and prolonged charge-carrier lifetimes. The final 2D/3D hybrid PSC exhibited a power conversion efficiency of 21.06% with excellent ambient stability (RH of 60%) without being encapsulated. In Chapter 3, the effect of molecular structure of organic spacer on the optoelectical property and operational stability of PSCs was investigated. Comparative study on thermal degradation behavior revealed that organic spacer with primary ammonium structure are vulnerable to deprotonation reaction under typical perovskite processing condition, thereby promoting the formation of iodine vacancy and metallic lead cluster on the perovskite surface. Meanwhile, bulky cation with quaternary ammonium structure exhibited exceptional chemical stability under perovskite processing condition. PTMA-I uniformly adsorbed on the surface of perovskite successfully passivated structural defects. PSC with PTMA-I could achieve PCE of 21.6% and stabilized efficiency of 20.5% with substantially improved operational stability: The PSC retained more than 85% of its initial PCE after 1000h operation under continuous illumination