Stable and Multifunctional Optoelectronic Devices via Organic-Inorganic Hybrid Perovskite

Abstract

Abstract Organic-inorganic hybrid perovskites (e.g. methylammonium lead iodide (MAPbI3) and formamidinium tin bromide (FASnBr3)) have attracted significant attention as a next-generation optoelectronic material due to their superior optical properties, bandgap tunability, low cost and facile fabrication methods. With such numerous advantages, the perovskites have been exploited as a key material for photovoltaics, photodetectors, light emitting diode, and other optoelectronic devices. However, the poor long-term stability of perovskite-based optoelectronic devices is a major obstacle to operating them in real-life environments, especially under humid conditions. The perovskite film is vulnerable to the degradation induced by the water molecules or polar solvents which can form a strong hydrogen bonding with organic chemicals within perovskite crystals. Therefore, development of a high-resistant perovskite film against water or polar solvent is prerequisite for achieving the long-term stability of perovskite-based optoelectronic devices. This thesis proposes novel film fabrication methods and strategies for achieving highly stable perovskite film and their relevant applications in optoelectronic devices. This thesis begins with an overview on representative perovskite-based optoelectronic devices including a solar cell and photodetector in chapter 1, in which key materials with their characteristics, general device structures, working principles and their limitations are described. Concerning the use of perovskite solar cells (PSCs) in real-life environments, long-term device stability under humid conditions need to be improved. In chapter 2, we describe the introduction to perovskite film fabrication based on a dip-spin coating method. The method is utilized in the perovskite solar cells using a mesoporous TiO2 electron transport layer to reduce intrinsic defects, pores, and voids at the interface between perovskite and TiO2 layers. The perovskite film possesses the uniform and large grains without surface voids via the dip-spin coating method, resulting in the enhanced device stability under nitrogen atmosphere. In the following chapter (chapter 3), a facile passivation method using polydimethylsiloxane (PDMS) for improving device stability of PSC against humid conditions is described. The PDMS passivates agent for perovskite grains and grain boundaries simultaneously by simple dropping a PDMS solution. The PDMS passivation inhibits the contact between water and perovskite film and reduces Pb defects in perovskite film by promoting a lead oxide bonding formation. Consequently, the device stability of PDMS-passivated PSC is remarkably enhanced compared to a reference PSC (without passivation), more than 90 % of the initial efficiency is sustained after 5000 h under 70 % relative humidity. These days, a multi-functionality of unit device is essential for low power consumption, circuit miniaturization, and spatial efficient integration, but the optoelectronic properties of most conventional perovskite-based devices have limited to single spectral response due to their simple device architecture (p-i-n diode configuration). The film fabrication techniques via multi-step methods allow of not only maintaining phase stability but also designing a sophisticated device architecture (e.g., multi-layered perovskite device). In chapter 4, we introduce the novel perovskite optoelectronic device which are exploited as perovskite filter-free photodetector (PFFD) using an integration of two different perovskite film into a back-to-back diode configuration. The PFFD device with p-i-n-i-p structure in which high-band and low-band perovskite films is vertically stacked allows selective charge extraction by switching bias polarity, resulting in accurate discrimination of red, green, and blue color without optical filters. Furthermore, an integrated PFFD platform has succeeded in discrimination of 16 arbitrary non-monochromatic colors. In last chapter (chapter 5) of this thesis, multi-functional optoelectronic logic gate device (OELG) via the back-to-back diode configuration consisting of visible and near infrared (NIR) perovskite absorbers is described. The OELG device exhibits bipolar spectral response by wavelength of incident light and it allows the photocurrent polarity control using optical gate modulation (auxiliary visible and NIR light). Five basic logic gates of "AND", "OR", "NAND", "NOR", and "NOT" are demonstrated with a single device based on the bipolar spectral response. In addition, integrated OELG platform consisting of 64 pixels executes five logic gate in 100 % accuracy irrelevant to current variation between pixels.