Nam-Gyu Park

Sungkyunkwan University | SKKU · School of Chemical Engineering

The exotic properties of three-dimensional halide perovskites, such as mixed ionic–electronic conductivity and feasible ion migration, have enabled them to challenge traditional memristive materials. However, the poor moisture stability and difficulty in controlling ion transport due to their polycrystalline nature have hindered their use as a neur...

It is critical to design the bifunctional passivation molecules to passivate simultaneously both charge transport layer and perovskite layer at the charge transport layer/perovskite interface in perovskite solar cells (PSCs)....

Halide perovskite single crystals (SCs) have attracted much attention for their application in high‐performance x‐ray detectors owing to their desirable properties, including low defect density, high mobility–lifetime product (μτ), and long carrier diffusion length. However, suppressing the inherent defects in perovskites and overcoming the ion mig...

Defect passivation based on Lewis acid–base chemistry has been regarded as an effective strategy to improve the photovoltaic performance and stability of perovskite solar cells (PSCs). Here, we report on tertiary phosphine oxides (R3PO) as materials for defect passivation, where photovoltaic performance was investigated depending on the substituent...

Organic-inorganic perovskite materials have gradually progressed from single-junction solar cells to tandem (double) or even multi-junction (triple-junction) solar cells as all-perovskite tandem solar cells (APTSCs) have advantages: (1) the tunable...

Since the certified power conversion efficiency (PCE) of perovskite solar cells (PSCs) has reached 26.1%, exactly equal to that of crystalline silicon solar cells, a strong demand for ensuring the long‐term stability of PSCs has arisen for commercialization. The intrinsic stability of the perovskite layer must be guaranteed as a top priority to ens...

The introduction of alkoxy side chains into the backbone of conjugated polymers is an effective way to change their properties. While the impact on the structure and optoelectronic properties of polymer thin films was well‐studied in organic solar cells and transistors, limited research has been conducted on their effects on doping and thermoelectr...

High-purity precursor materials are vital for high-efficiency perovskite solar cells (PSCs) to reduce defect density caused by impurities in perovskite. In this study, we present aqueous synthesized perovskite microcrystals as precursor materials for PSCs. Our approach enables kilogram-scale mass production and synthesizes formamidinium lead iodide...

Hygroscopic and acidic nature of organic hole transport layers (HTLs) insisted to replace it with metal oxide semiconductors due to their favorable charge carrier transport with long chemical stability. Apart from large direct bandgap and high optical transmittance, ionization energy in the range of −5.0 to −5.4 eV leads to use NiO as HTL due to go...

Metal halide perovskite solar cells (PSCs) are infamous for their batch‐to‐batch and lab‐to‐lab irreproducibility in terms of stability and performance. Reproducible fabrication of PSCs is a critical requirement for market viability and practical commercialization. PSC irreproducibility plagues all levels of the community; from institutional resear...

In this study, eutectic gallium–indium alloy (EGaIn) liquid metal is used as the rear electrode for perovskite solar cells (PSCs), where the interfacial properties of the device, particularly the beneficial roles of the surface oxide of the liquid metal, are explored. The findings demonstrate that the native oxide of the EGaIn electrode significant...

Perovskite solar cells (PSCs) composing the formula of FA1-xCsxPbI3 provide an attractive ption for integrating high efficiency, durable stability and compatibility with upscale fabrication. Despite the Cs cation incorporation potentially enabling a perfect perovskite lattice1,2, the compositional inhomogeneity caused by A-site cation segregation i...

Understanding the interplay between the surface structure and the passivation materials and their effects associated with surface structure modification is of fundamental importance; however, it remains an unsolved problem in the perovskite passivation field. Here, we report a surface passivation principle for efficient perovskite solar cells via a...

In a two‐step procedure for fabricating perovskite films, the PbI2 layer formed on the substrate is converted to perovskite by reacting PbI2 with organic iodide. Excess PbI2 left after forming perovskite composition, however, might have an ill effect on device stability and current–voltage hysteresis, although it positively affects efficiency impro...

Preliminary theoretical analyses indicate that lattice relaxation may be used to release lattice strain in the FAPbI3 perovskite to warrant both high x-ray detection performance and improved stability. Herein, we demonstrate stable black α-phase FAPbI3 single crystals (SCs) realized by lattice engineering via annealing in the ambient atmosphere. Th...

Significant reduction of light-induced halide segregation in organic–inorganic lead mixed-halide perovskites is essential for their implementation in tandem solar cells with existing silicon technology. Here, we address this challenge by a “One-stone-for-two-birds” strategy in which superhalogen anions of the molecular additive facilitate the reduc...

Post-treatment of formamidinium lead triiodide (FAPbI3) with ammonium halogen salts, such as phenethylammonium or octylammonium iodide, has been widely used to improve the photovoltaic performance and stability of perovskite solar cells (PSCs) via surface defect passivation. Although the passivation is expected to be influenced by functional groups...

Excess lead(II) iodide (PbI2) has controversial roles in affecting the efficiency of perovskite solar cells (PSCs). Since the photoinstability of PbI2 is now known to largely accelerate perovskite degradation, suppressing and/or eliminating excess PbI2 is key to improving the stability of PSCs. Herein, process‐dependent PbI2 formation on the surfac...

Lead halide perovskites are promising semiconducting materials for solar energy harvesting. However, the presence of heavy-metal lead ions is problematic when considering potential harmful leakage into the environment from broken cells and also from a public acceptance point of view. Moreover, strict legislation on the use of lead around the world...

Electron transport layers (ETLs) are imperative in n-i-p structured perovskite solar cells (PSCs) because of their capability to affect light propagation, electron extraction, and perovskite crystallization, and any mismatch of optical constants, band position, and surface potential between the ETLs and the perovskites can cause unintentional optic...

Methylammonium chloride (MACl) has been used as an additive in a formamidinium lead iodide (FAPbI3) precursor solution for high-efficiency perovskite solar cells (PCSs), where the chloride ion is known to have a positive effect on photovoltaic performance. However, we have found that the residual chloride in the perovskite film has an adverse effec...

Crystallization kinetic controls the crystallographic orientation, inducing anisotropic properties of the materials. As a result, preferential orientation with advanced optoelectronic properties can enhance the photovoltaic devices' performance. Although incorporation of additives is one of the most studied methods to stabilize the photoactive α-ph...

Since the groundbreaking report on solid-state perovskite solar cells (PSCs) in 2012, PSC receives great attention due to its high power conversion efficiency (PCE) obtainable at low-cost fabrication. A PCE of 9.7% in 2012 was swiftly improved to 25.7% in 2022 via perovskite composition engineering and grain size control. The excellent photovoltaic...

As a power conversion efficiency (PCE) of perovskite solar cells (PSCs) has rapidly increased up to 25.7% in 2022, a curiosity about the achievable limit of PCE has prevailed and demands understanding about the underlying fundamentals to step forward. Meanwhile, outstanding long‐term stability of PSCs over 1000 h has been reported at operating cond...

Low-temperature processed SnO2 is a promising electron transporting layer in perovskite solar cells (PSCs) due to its optoelectronic advantage. Atomic layer deposition (ALD) is suitable for forming a conformal SnO2 layer on a high-haze substrate. However, oxygen vacancy formed by the conventional ALD process using H2O might have a detrimental effec...

Organic–inorganic or inorganic metal halide materials have emerged as a promising candidate for a resistive switching material owing to their ability to achieve low operating voltage, high on–off ratio, and multi‐level switching. However, the high switching variation, limited endurance, and poor reproducibility of the device hinder practical use of...

Chemical bath-deposited SnO2 has been widely used as an electron transport layer for high-efficiency perovskite solar cells (PSCs). However, the solution-processed SnO2 has -OH groups on its surface due to proton-rich condition, which degrades the stability and efficiency of PSCs. In this study, we report on an effective way to reduce the density o...

A myriad of studies and strategies have already been devoted to improving the stability of perovskite films; however, the role of the different perovskite crystal facets in stability is still unknown. Here, we reveal the underlying mechanisms of facet-dependent degradation of formamidinium lead iodide (FAPbI3) films. We show that the (100) facet is...

Apart from the photovoltaic effect, we report here for the first time on the ionovoltaic effect of 2-dimensional (2D) halide perovskite located between vertically installed electrode structures, generating electricity by...

Cations with suitable sizes to occupy an interstitial site of perovskite crystals have been widely used to inhibit ion migration and promote the performance and stability of perovskite optoelectronics. However, such interstitial doping inevitably leads to lattice microstrain that impairs the long-range ordering and stability of the crystals, causin...

Lead halide perovskite solar cells (PSCs) have been considered one of the most promising candidates for future energy supply, whereas just solar cell does not guarantee sustainability. Owing to the ionic nature and constituent heavy metals, perovskite materials are prone to decay under operating conditions and pose a threat to ecosystems and human...

Perovskite solar cells (PSCs) are rivaling most commercial photovoltaics in the aspect of efficiency and cost, while their intrinsic instability remains a major concern for their practical deployment. The presence of undesirable strain in PSCs during device fabrication and operation refers to the extension/narrowing of chemical bonds and expansion/...

Discovering the top-performing facets of perovskite crystals holds the secret to highly efficient perovskite solar cells (PSCs). However, the dominated facet properties of perovskite (i.e., (100), (110), (111) facets) remain elusive. Here, we demonstrate that exquisite control of the perovskite film formation enables the formation of perovskite pol...

Perovskite solar cells (PSCs) are rivaling most commercial photovoltaics in the aspect of efficiency and cost, while the intrinsic instability remains a major concern for their practical deployment. The presence of undesirable strain in PSCs during device fabrication and operation refers to extension/narrowing of chemical bonds and expansion/shrink...

Organic−inorganic hybrid perovskites display remarkable photovoltaic properties, but instability arises from the material’s surface and photoexcitation. The photodegradation process of methylammonium lead triiodide (MAPbI3) investigated with above bandgap excitation Raman spectroscopy displays two stages of structural change in polycrystalline film...

Flexible perovskite solar cells (f-PSCs) have attracted increasing attention for a variety of applications because of their desirable form factor and improved durability. However, the f-PSC fabrication process has not been optimized, resulting in their uneven efficiency. We report a van der Waals stacking (vdWS) process that yields uniform and high...

Optoelectronic devices consist of heterointerfaces formed between dissimilar semiconducting materials. The relative energy level alignment between contacting semiconductors determinately affects the heterointerface charge injection and extraction dynamics. For perovskite solar cells (PSCs), the heterointerface between the top perovskite surface and...

For valence change memory (VCM)‐type synapses, a large number of vacancies help to achieve very linearly changed dynamic range, and also, the low activation energy of vacancies enables low‐voltage operation. However, a large number of vacancies increases the current of artificial synapses by acting like dopants, which aggravates low‐energy operatio...

To approach the theoretical efficiency of perovskite solar cells (PSCs), the defects in perovskites should be managed. Among different types of defects, halide vacancies easily form on the surface of perovskite grains (PGs), hindering perovskite stability and the charge-transport process by trapping charge carriers. In this work, oxidized black pho...

Stacked perovskite films—laminated films in particular—have garnered considerable attention owing to their excellent potential for various applications. However, perovskite solar cells fabricated using laminated perovskite films exhibit a critically low power conversion efficiency. To overcome this limitation, in this paper, we report the surface a...

The A cation in ABX3 organic-inorganic lead halide perovskites (OLHPs) was conventionally believed to hardly affect their optoelectronic properties. However, more recent developments have unraveled the critical role of the A cation in the regulation of the physicochemical and optoelectronic properties of OLHPs. We review the important breakthroughs...

Although perovskite solar cell exhibits power conversion efficiency as high as 25.5%, the occurrence of anomalous hysteresis in current density ( J )–voltage ( V ) performance has been issued because the hysteresis can have negative effects on not only efficiency but also stability. Therefore, it is important to find solutions to solve the hysteric...

Following the 1st release of the “Emerging photovoltaic (PV) reports”, the best achievements in the performance of emerging photovoltaic devices in diverse emerging photovoltaic research subjects are summarized, as reported in peer‐reviewed articles in academic journals since August 2020. Updated graphs, tables, and analyses are provided with sever...

In order to further improve power conversion efficiency (PCE) toward Shockley−Queisser limit efficiency approaching 32% for a single‐junction perovskite solar cell (PSC) based on a lead halide perovskite with a bandgap of about 1.45 eV, it is important to improve significantly open‐circuit voltage and fill factor without sacrificing short‐circuit c...

2D Perovskites In article number 2102236, Jong Hyeok Park, Nam-Gyu Park, Hyunjung Shin and co-workers extract photo-generated holes from 3D bulk perovskites of FAPbI3 through cyclohexylamonium-based 2D perovskites. 2D/3D perovskite heterojunction structures are successfully fabricated and the efficient extraction of holes is expressed in this cover...

Perovskite solar cells (PSCs) employing formamidinium lead iodide (FAPbI3) have shown high efficiency. However, operational stability has been issued due to phase instability of α phase FAPbI3 at ambient temperature. Excess precursors in the perovskite precursor solution has been proposed to improve not only power conversion efficiency (PCE) but al...

Halide perovskites, fascinating memristive materials owing to mixed ionic-electronic conductivity, have been attracting great attention as artificial synapses recently. However, polycrystalline nature in thin film form and instability under ambient air hamper them to be implemented in demonstrating reliable neuromorphic devices. Here, we successful...