The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.

Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells

Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

Lead halide perovskite solar cells have recently attracted tremendous attention because of their excellent photovoltaic efficiencies. However, the poor stability of both the perovskite material and the charge transport layers has so far prevented the fabrication of devices that can withstand sustained operation under normal conditions. Here, we report a solution-processed lead halide perovskite solar cell that has p-type NiOx and n-type ZnO nanoparticles as hole and electron transport layers, respectively, and shows improved stability against water and oxygen degradation when compared with devices with organic charge transport layers. Our cells have a p–i–n structure (glass/indium tin oxide/NiOx/perovskite/ZnO/Al), in which the ZnO layer isolates the perovskite and Al layers, thus preventing degradation. After 60 days storage in air at room temperature, our all-metal-oxide devices retain about 90% of their original efficiency, unlike control devices made with organic transport layers, which undergo a complete degradation after just 5 days. The initial power conversion efficiency of our devices is 14.6 ± 1.5%, with an uncertified maximum value of 16.1%. Using metal oxides for both the hole- and electron-transport layers in perovskite solar cells significantly improves their stability compared with devices containing organic transport layers.

Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers

Optical transparency, tunable conducting properties and easy processability make metal oxides key materials for advanced optoelectronic devices. This Review discusses recent advances in the synthesis of these materials and their use in applications. Metal oxides (MOs) are the most abundant materials in the Earth's crust and are ingredients in traditional ceramics. MO semiconductors are strikingly different from conventional inorganic semiconductors such as silicon and III–V compounds with respect to materials design concepts, electronic structure, charge transport mechanisms, defect states, thin-film processing and optoelectronic properties, thereby enabling both conventional and completely new functions. Recently, remarkable advances in MO semiconductors for electronics have been achieved, including the discovery and characterization of new transparent conducting oxides, realization of p-type along with traditional n-type MO semiconductors for transistors, p–n junctions and complementary circuits, formulations for printing MO electronics and, most importantly, commercialization of amorphous oxide semiconductors for flat panel displays. This Review surveys the uniqueness and universality of MOs versus other unconventional electronic materials in terms of materials chemistry and physics, electronic characteristics, thin-film fabrication strategies and selected applications in thin-film transistors, solar cells, diodes and memories.

Metal oxides for optoelectronic applications

Methylammonium Chloride Induces Intermediate Phase Stabilization for Efficient Perovskite Solar Cells

Interface engineering of β-Ga2O3 MOS-type Schottky barrier diode using an ultrathin HfO2 interlayer

We report the effects of high-pressure annealing (HPA) on solution-processed InGaZnO (IGZO) thin-film transistors (TFTs). HPA increased the density of IGZO films. In particular, annealing in O2 at 1.0 MPa and 350 °C resulted in a high-density and low-porosity IGZO film, as characterized using X-ray reflectivity (XRR) and ellipsometry measurements. This was attributed to the oxidative and compressive effects on the oxygen-deficient solution-processed IGZO film. TFTs annealed in O2 at 1.0 MPa and 350 °C exhibited an increase in the field-effect mobility by a factor of approximately five compared with TFTs annealed in air at 0.1 MPa and 350 °C. Furthermore, improvements in reliability under negative and positive bias stresses were also observed following HPA.

Densification effects on solution-processed indium–gallium–zinc–oxide films and their thin-film transistors

The effects of oxygen high-pressure annealing (O
 2
 HPA) on the performance and instability of amorphous Ge-In-Ga-O (a-GIGO) thin-film transistors (TFTs) were examined. The TFTs with HPA under 30 atm O
 2
 ambient exhibited consistently better stability against the applied temperature stress and positive gate bias stress. We demonstrate that the superior stability of the HPA-treated device can be correlated with the evolution of electronic structure in a-GIGO thin films, as measured by spectroscopic ellipsometry, which reveals the significantly reduced band edge states below the conduction band by the O
 2
 HPA treatment. Based on the Meyer-Neldel rule, the total density of subgap states energy distribution, including the interfacial and semiconductor bulk trap densities, was also extracted and compared, which can support the experimental observation.

The Influence of Oxygen High-Pressure Annealing on the Performance and Bias Instability of Amorphous Ge–In–Ga–O Thin-Film Transistors

Methods of forming an oxide material layer are provided. The method includes mixing a precursor material with a peroxide material to form a precursor solution, coating the precursor solution on a substrate, and baking the coated precursor solution.

Compositions used in formation of oxide material layers, methods of forming an oxide material layer using the same, and methods of fabricating a thin film transistor using same

— In this article, a solution process for oxide thin-film transistors (TFTs) at low-temperature annealing was investigated. Solution-process engineering, including materials and precursors, plays an important role in oxide thin-film deposition on large glass and flexible substrates at low temperature. Reactive material could reduce the alloy reaction temperature for a multicomponent oxide system. A volatile precursor could also reduce annealing temperature in the formation of metal-oxide thin films. A solution process with reactive Al and a volatile nitrate precursor can demonstrates competitive oxide TFTs at 350°C.

You Seung Rim

Papers

Interface engineering of β-Ga2O3 MOS-type Schottky barrier diode using an ultrathin HfO2 interlayer

Densification effects on solution-processed indium–gallium–zinc–oxide films and their thin-film transistors

The Influence of Oxygen High-Pressure Annealing on the Performance and Bias Instability of Amorphous Ge–In–Ga–O Thin-Film Transistors

Compositions used in formation of oxide material layers, methods of forming an oxide material layer using the same, and methods of fabricating a thin film transistor using same

Solution-processed oxide thin-film transistors using aluminum and nitrate precursors for low-temperature annealing