Sanggyun Kim
Advisor: Prof. Juan-Pablo Correa-Baena

will defend a doctoral thesis entitled,

Organic Electronic Interlayers for Long-Term Stability of Hybrid Perovskite Solar Cells

On

Tuesday, May 27th at 01:00 p.m.

Marcus Nanotechnology Building, Conference Room 1117-1118

Committee
            Prof. Juan-Pablo Correa-Baena – School of Materials Science and Engineering & School of Chemistry and Biochemistry (advisor)
            Prof. John R. Reynolds – School of Chemistry and Biochemistry & School of Materials Science and Engineering
            Prof. Ajeet Rohatgi – School of Electrical and Computer Engineering

 Prof. Jason Azoulay – School of Chemistry and Biochemistry & School of Materials Science and Engineering

            Prof. Anju Toor – School of Materials Science and Engineering

Abstract

Hybrid organic-inorganic perovskite (HOIP) solar cells have witnessed remarkable progress in power conversion efficiency over the past 16 years, now reaching certified values as high as 26.95%. Despite these impressive efficiency gains, long-term operational stability remains a significant barrier to commercialization. A key contributor to this limitation is the instability of charge transport layers (CTLs) and their interfaces with the perovskite absorber layer, which are particularly susceptible to degradation mechanisms such as cracking, delamination, ion migration, interfacial chemical reactions. These instabilities compromise the structural and electronic integrity of perovskite solar cells (PSCs), underscoring the need for a deeper understanding of the interlayer degradation processes. This dissertation aims to elucidate the multifaceted role of interlayers in governing PSC long-terms stability with a focus on integrating novel organic CTLs, including conjugated polymers (CPs) and small molecules.

The first thrust focuses on comprehensive examination of 1,4-bis(2-thienyl)-2,5-dialkoxyphenylene based CPs as a hole transport layers (HTLs) in PSCs. This study establishes a clear correlation between the high thermal transition temperatures of CP HTLs and the enhanced thermal stability of CP integrated PSCs. Building on these findings, the second thrust explores naphthalene diimide (NDI)-based molecules as potential electron transport layers (ETLs). Here, special attention is given to the role of anchoring groups in governing interfacial interaction with both transparent conductive oxides (TCOs) and the perovskite layer. Anchoring groups on the ETL enable strong covalent bonding to TCO surfaces, acting as key determinants of interfacial adhesion and long-term stability in PSC. The third thrust investigates the lowest unoccupied molecular orbital (LUMO) level engineering in NDI-based molecules through core modification with electron-withdrawing substituents. This tuning strategy lowers the LUMO level to improve energetic alignment with the perovskite conduction band minimum, reducing the electron extraction barrier and suppressing interfacial charge accumulation. As a result, carrier extraction becomes more efficient, current density-voltage hysteresis is mitigated, and overall device performance is enhanced.

A multidisciplinary methodology is employed through this work, combining structural, surface, and optoelectronic characterization with device-level performance analyses. These comprehensive studies demonstrate the significant impact of organic CTLs on PSC stability and offer valuable strategies for interface engineering. In doing so, this research contributes to broader understanding of PSC operation and lays the groundwork for developing more robust and high-performance photovoltaic (PV) technologies.