S-Space College of Engineering/Engineering Practice School (공과대학/대학원) Dept. of Material Science and Engineering (재료공학부) Theses (Ph.D. / Sc.D._재료공학부)
A Study on Charge Collecting Property of Semiconducting Oxide Materials in Photoelectric Energy Conversion System
광·전 에너지 변환 시스템 내 산화물 반도체 물질의 전하 수집 능력 제어에 관한 연구
- Park, Jong Hoon
- 공과대학 재료공학부
- Issue Date
- 서울대학교 대학원
- 학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2015. 8. 황철성.
- Nanostructured transparent n-type and p-type semiconducting oxides were
synthesized and designed for enhancing device performance in photoelectric
energy conversion system. The synthesized nanostructures were used as
photoelectrodes and applied to photovoltaic devices, particularly in emerging
photovoltaic (PV) system. The correlation between structural/compositional
design of the photoelectrodes and their charge collecting property was
explored. Concretely, inorganic semiconductor sensitized solar cells (ISSCs)
and organic-inorganic hybrid perovskite solar cells (PSCs), which are acceptable as typical emerging PVs in economic terms for environment
conservation and energy generation, were studied. These ISSCs and PSCs
currently face significant challenges in improving energy conversion
efficiency and environmental stability. Since n-type and p-type
semiconducting oxide based photoelectrodes are essential in charge collecting
ability of photovoltaic devices, control and design of fundamental properties
of semiconducting oxides are needed to overcome the above challenges. From
this point of view, this thesis proposes two strategies for efficient charge
collecting property in ISSCs and PSCs. First is structural design of
semiconducting oxides. Second is compositional design of semiconducting
oxides for effective charge injection from light absorbers to electron acceptors.
First, n-type titanium dioxide (TiO2) and p-type nickel oxide (NiO)
semiconducting oxides were explored to investigate the structural effect on
electron-hole recombination and overall charge collecting property in
emerging PV devices. For TiO2, hierarchically organized nano-architectures
containing both large surface area and open channels of pores were
synthesized on glass substrates using pulsed laser deposition (PLD) system.
Growth mechanism of the architectures was studied and their charge
collecting property in ISSCs was investigated. It was found that the
morphology of photoelectrode strongly influenced the device performance.
The open channels of pores between the TiO2 domains which generated by the
unique form of the architecture induced the infiltration of inorganic
semiconductors (IS) and liquid polysulfide electrolytes more rapidly, resulting
in higher light harvesting (efficient absorption of IS) and longer electron lifetime compared to the conventional TiO2 nanoparticle film. The enhanced
light harvesting and charge collecting property led to the enhancement of
overall energy conversion efficiency of the devices. Additionally, the larger
surface area of nano-architecture further enhanced the light harvesting
efficiency. For NiO, highly transparent, (111)-preferred oriented, columnshaped
nanostructured films were grown on glass substrates and the optimum
microstructure of NiO as hole transporting layer (HTL) for PSCs was
investigated using PLD system. The device performance was explored using a
p-i-n type PSCs, which is based on NiO/MAPbI3/PCBM configuration.
Compared to that of densely-packed NiO thin film or porous film, the overall
efficiency was significantly enhanced with the nanostructured NiO film. The
enhanced performance was attributed to the suppressed recombination rate
during the extraction and transportation of the dissociated carriers.
Second, compositional design of TiO2 nanostructured films was explored
to enhance the charge injection property between light absorbing materials
and electron accepting semiconducting oxides in ISSCs. From the basis that
the energy difference between the conduction band (CB) of IS and TiO2 serves
as the driving force for electron injection and that the doping metal cation into
TiO2 lattice alters the CB position of TiO2, the enhanced charge injection
ability of TiO2 was expected by Niobium (Nb) doping. The relationship
between the Nb doping and their effects on the final photovoltaic device
performance were investigated. As a consequence, the generated
photocurrents were greatly improved by Nb doping compared to the undoped
ISSC. The enhanced photocurrents and overall energy conversion efficiency were attributed to the efficient electron injection between IS and Nb doped
TiO2, resulted from the enlarged energy difference of the CB edge between IS
and TiO2 by introduction of Nb dopants.
This thesis focused on understanding of the relation between the
structural/compositional design of semiconducting oxides and their effect on
charge collecting property in photoelectric energy conversion system.
Through the study, this thesis proposes a guideline of designing the
semiconducting oxide based photoelectrode and a possibility to solve the
faced challenges in the fields of emerging PVs.