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Ao Liu

Pohang University of Science and Technology · Engineering

About the Lab

Professor Ao Liu's research lab specializes in the development of solution-processed oxide semiconductors and perovskite materials for next-generation optoelectronic devices. The lab focuses on low-temperature fabrication techniques, defect passivation strategies, and dielectric engineering to enhance the performance and stability of thin-film transistors and perovskite solar cells. Key research directions include p-type and n-type oxide semiconductors, high-κ dielectrics, and interface engineering for efficient charge transport and reduced recombination losses. The lab emphasizes scalable, low-cost, and environmentally friendly processing methods for large-area, flexible, and transparent electronics.

oxide semiconductorsperovskite solar cellsthin-film transistorslow-temperature processingdefect passivation

Research Overview

Papers
399
Total Citations
12,123
Papers (5y)
206
Primary Field
Engineering

Research Output Trend

Figures are computed from collected data and may differ slightly.

Publications per year (5y)
206total
2022
2023
2024
2025
2026
Citations per year (5y)
3,620total
20222023202420252026

Selected Papers

15
1
Article|680 citations·2023
Bimolecularly passivated interface enables efficient and stable inverted perovskite solar cells
Cheng Liu, Yi Yang, Hao Chen, Jian Xu, Ao Liu, Abdulaziz S. R. Bati, Huihui Zhu, Luke Grater, Shreyash Hadke, Chuying Huang, Vinod K. Sangwan, Tong Cai
SJR Q1ScienceOA

Compared with the n-i-p structure, inverted (p-i-n) perovskite solar cells (PSCs) promise increased operating stability, but these photovoltaic cells often exhibit lower power conversion efficiencies (PCEs) because of nonradiative recombination losses, particularly at the perovskite/C 60 interface. We passivated surface defects and enabled reflection of minority carriers from the interface into the bulk using two types of functional molecules. We used sulfur-modified methylthio molecules to pass

Electrical and Electronic EngineeringEngineering
2
Article|271 citations·2022
High-performance inorganic metal halide perovskite transistors
Ao Liu, Huihui Zhu, Sai Bai, Youjin Reo, Taoyu Zou, Myung‐Gil Kim, Yong‐Young Noh
SJR Q1Nature ElectronicsOA

Abstract The p-type characteristic of solution-processed metal halide perovskite transistors means that they could be used in combination with their n-type counterparts, such as indium–gallium–zinc-oxide transistors, to create complementary metal–oxide–semiconductor-like circuits. However, the performance and stability of perovskite-based transistors do not yet match their n-type counterparts, which limit their broader application. Here we report high-performance p-channel perovskite thin-film t

Electrical and Electronic EngineeringEngineering
3
Review|210 citations·2018
Solution Processed Metal Oxide High‐κ Dielectrics for Emerging Transistors and Circuits
Ao Liu, Huihui Zhu, Huabin Sun, Yong Xu, Yong‐Young Noh
SJR Q1Advanced Materials

Abstract The electronic functionalities of metal oxides comprise conductors, semiconductors, and insulators. Metal oxides have attracted great interest for construction of large‐area electronics, particularly thin‐film transistors (TFTs), for their high optical transparency, excellent chemical and thermal stability, and mechanical tolerance. High‐permittivity (κ) oxide dielectrics are a key component for achieving low‐voltage and high‐performance TFTs. With the expanding integration of complemen

Electrical and Electronic EngineeringEngineering
4
Article|202 citations·2021
The gas sensor utilizing polyaniline/ MoS2 nanosheets/ SnO2 nanotubes for the room temperature detection of ammonia
Ao Liu, Siyuan Lv, Jiang Li, Fangmeng Liu, Lianjing Zhao, Jing Wang, Xiaolong Hu, Zijie Yang, Junming He, Chenguang Wang, Xu Yan, Peng Sun
SJR Q1Sensors and Actuators B Chemical
Electrical and Electronic EngineeringEngineering
5
Article|191 citations·2017
Solution Combustion Synthesis: Low‐Temperature Processing for p‐Type Cu:NiO Thin Films for Transparent Electronics
Ao Liu, Huihui Zhu, Zidong Guo, You Meng, Ao Liu, Elvira Fortunato, Rodrigo Martins, Fukai Shan
SJR Q1Advanced Materials

Low‐temperature solution processing opens a new window for the fabrication of oxide semiconductors due to its simple, low cost, and large‐area uniformity. Herein, by using solution combustion synthesis (SCS), p‐type Cu‐doped NiO (Cu:NiO) thin films are fabricated at a temperature lower than 150 °C. The light doping of Cu substitutes the Ni site and disperses the valence band of the NiO matrix, leading to an enhanced p‐type conductivity. Their integration into thin‐film transistors (TFTs) demonst

Electrical and Electronic EngineeringEngineering
6
Article|183 citations·2014
Fully Solution-Processed Low-Voltage Aqueous In2O3 Thin-Film Transistors Using an Ultrathin ZrOx Dielectric
Ao Liu, Guo Xia Liu, Hui Hui Zhu, Feng Xu, Elvira Fortunato, Rodrigo Martins, Fu Kai Shan
SJR Q1ACS Applied Materials & Interfaces

We reported here "aqueous-route" fabrication of In2O3 thin-film transistors (TFTs) using an ultrathin solution-processed ZrOx dielectric thin film. The formation and properties of In2O3 thin films under various annealing temperatures were intensively examined by thermogravimetric analysis, Fourier transform infrared spectroscopy, and atomic force microscopy. The solution-processed ZrOx thin film followed by sequential UV/ozone treatment and low-temperature thermal-annealing processes showed an a

Electrical and Electronic EngineeringEngineering
7
Article|182 citations·2015
Low‐Temperature, Nontoxic Water‐Induced Metal‐Oxide Thin Films and Their Application in Thin‐Film Transistors
Ao Liu, Ao Liu, Huihui Zhu, Byoungchul Shin, Elvira Fortunato, Rodrigo Martins, Yiqian Wang, Fukai Shan
SJR Q1Advanced Functional Materials

Here, a simple, nontoxic, and inexpensive “water‐inducement” technique for the fabrication of oxide thin films at low annealing temperatures is reported. For water‐induced (WI) precursor solution, the solvent is composed of water without additional organic additives and catalysts. The thermogravimetric analysis indicates that the annealing temperature can be lowered by prolonging the annealing time. A systematic study is carried out to reveal the annealing condition dependence on the performance

Electrical and Electronic EngineeringEngineering
8
Article|179 citations·2018
Room‐Temperature Solution‐Synthesized p‐Type Copper(I) Iodide Semiconductors for Transparent Thin‐Film Transistors and Complementary Electronics
Ao Liu, Huihui Zhu, Won‐Tae Park, Seok‐Ju Kang, Yong Xu, Myung‐Gil Kim, Yong‐Young Noh
SJR Q1Advanced Materials

Abstract Here, room‐temperature solution‐processed inorganic p‐type copper iodide (CuI) thin‐film transistors (TFTs) are reported for the first time. The spin‐coated 5 nm thick CuI film has average hole mobility ( µ FE ) of 0.44 cm 2 V −1 s −1 and on/off current ratio of 5 × 10 2 . Furthermore, µ FE increases to 1.93 cm 2 V −1 s −1 and operating voltage significantly reduces from 60 to 5 V by using a high permittivity ZrO 2 dielectric layer replacing traditional SiO 2 . Transparent complementary

Electrical and Electronic EngineeringEngineering
9
Article|174 citations·2015
Water‐Induced Scandium Oxide Dielectric for Low‐Operating Voltage n‐ and p‐Type Metal‐Oxide Thin‐Film Transistors
Ao Liu, Ao Liu, Huihui Zhu, Huijun Song, Byoungchul Shin, Elvira Fortunato, Rodrigo Martins, Fukai Shan
SJR Q1Advanced Functional Materials

Solution‐processed metal‐oxide thin films based on high dielectric constant ( k ) materials have been extensively studied for use in low‐cost and high‐performance thin‐film transistors (TFTs). Here, scandium oxide (ScO x ) is fabricated as a TFT dielectric with excellent electrical properties using a novel water‐inducement method. The thin films are annealed at various temperatures and characterized by using X‐ray diffraction, atomic‐force microscopy, X‐ray photoelectron spectroscopy, optical sp

Electrical and Electronic EngineeringEngineering
10
Review|169 citations·2021
Engineering Copper Iodide (CuI) for Multifunctional p‐Type Transparent Semiconductors and Conductors
Ao Liu, Huihui Zhu, Myung‐Gil Kim, Junghwan Kim, Yong‐Young Noh
SJR Q1Advanced ScienceOA

Developing transparent p-type semiconductors and conductors has attracted significant interest in both academia and industry because metal oxides only show efficient n-type characteristics at room temperature. Among the different candidates, copper iodide (CuI) is one of the most promising p-type materials because of its widely adjustable conductivity from transparent electrodes to semiconducting layers in transistors. CuI can form thin films with high transparency in the visible light region us

Materials ChemistryMaterials Science
11
Article|164 citations·2020
High-performance p-channel transistors with transparent Zn doped-CuI
Ao Liu, Huihui Zhu, Won‐Tae Park, Sejun Kim, Hyungjun Kim, Myung‐Gil Kim, Yong‐Young Noh
SJR Q1Nature CommunicationsOA

Abstract ‘Ideal’ transparent p -type semiconductors are required for the integration of high-performance thin-film transistors (TFTs) and circuits. Although CuI has recently attracted attention owing to its excellent opto-electrical properties, solution processability, and low-temperature synthesis, the uncontrolled copper vacancy generation and subsequent excessive hole doping hinder its use as a semiconductor material in TFT devices. In this study, we propose a doping approach through soft che

Electrical and Electronic EngineeringEngineering
12
Article|151 citations·2016
Hole mobility modulation of solution-processed nickel oxide thin-film transistor based on high-k dielectric
Ao Liu, Ao Liu, Huihui Zhu, Byoungchul Shin, Elvira Fortunato, Rodrigo Martins, Fukai Shan
SJR Q1Applied Physics Letters

Solution-processed p-type oxide semiconductors have recently attracted increasing interests for the applications in low-cost optoelectronic devices and low-power consumption complementary metal-oxide-semiconductor circuits. In this work, p-type nickel oxide (NiOx) thin films were prepared using low-temperature solution process and integrated as the channel layer in thin-film transistors (TFTs). The electrical properties of NiOx TFTs, together with the characteristics of NiOx thin films, were sys

Electrical and Electronic EngineeringEngineering
13
Article|150 citations·2023
High-performance metal halide perovskite transistors
Ao Liu, Huihui Zhu, Sai Bai, Youjin Reo, Mario Caironi, Annamaria Petrozza, Letian Dou, Yong‐Young Noh
SJR Q1Nature Electronics
Electrical and Electronic EngineeringEngineering
14
Article|134 citations·2024
Selenium-alloyed tellurium oxide for amorphous p-channel transistors
Ao Liu, Yong‐Sung Kim, Min Gyu Kim, Youjin Reo, Taoyu Zou, Taesu Choi, Sai Bai, Huihui Zhu, Yong‐Young Noh
SJR Q1NatureOA

Abstract Compared to polycrystalline semiconductors, amorphous semiconductors offer inherent cost-effective, simple and uniform manufacturing. Traditional amorphous hydrogenated Si falls short in electrical properties, necessitating the exploration of new materials. The creation of high-mobility amorphous n-type metal oxides, such as a-InGaZnO (ref. 1 ), and their integration into thin-film transistors (TFTs) have propelled advancements in modern large-area electronics and new-generation display

Electrical and Electronic EngineeringEngineering
15
Article|108 citations·2016
High-mobility p-type NiOx thin-film transistors processed at low temperatures with Al2O3 high-k dielectric
Fukai Shan, Ao Liu, Huihui Zhu, Weijin Kong, Jingquan Liu, Byoungchul Shin, Elvira Fortunato, Rodrigo Martins, Ao Liu
SJR Q1Journal of Materials Chemistry C

High-performance p-type NiO<sub>x</sub> thin-film transistors are fabricated <italic>via</italic> a low-cost solution process and exhibit a high mobility of around 15 cm<sup>2</sup> V<sup>−1</sup> s<sup>−1</sup>.

Electrical and Electronic EngineeringEngineering

Research Areas

Electrical and Electronic EngineeringMaterials ChemistryMolecular BiologyMechanical EngineeringBiomedical EngineeringAerospace Engineering

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