Haijuan Zhang

Bio: Haijuan Zhang is an academic researcher from Center for Advanced Materials. The author has contributed to research in topics: Perovskite (structure) & PEDOT:PSS. The author has an hindex of 6, co-authored 8 publications receiving 575 citations.

Lead-Free Organic-Inorganic Hybrid Perovskites for Photovoltaic Applications: Recent Advances and Perspectives.

Abstract: Organic-inorganic hybrid halide perovskites (e.g., MAPbI3 ) have recently emerged as novel active materials for photovoltaic applications with power conversion efficiency over 22%. Conventional perovskite solar cells (PSCs); however, suffer the issue that lead is toxic to the environment and organisms for a long time and is hard to excrete from the body. Therefore, it is imperative to find environmentally-friendly metal ions to replace lead for the further development of PSCs. Previous work has demonstrated that Sn, Ge, Cu, Bi, and Sb ions could be used as alternative ions in perovskite configurations to form a new environmentally-friendly lead-free perovskite structure. Here, we review recent progress on lead-free PSCs in terms of the theoretical insight and experimental explorations of the crystal structure of lead-free perovskite, thin film deposition, and device performance. We also discuss the importance of obtaining further understanding of the fundamental properties of lead-free hybrid perovskites, especially those related to photophysics.

Enhancing Efficiency and Stability of Perovskite Solar Cells via a Self-Assembled Dopamine Interfacial Layer.

Abstract: Interfacial engineering is a simple and effective strategy that can improve the photovoltaic performance in organic–inorganic perovskite solar cells (PSCs). Herein, a dopamine (DA) self-assembled monolayer (SAM) was introduced on the top of the SnO2 electron transporting layer (ETL) to modify the SnO2/perovskite interface. The processing temperature of the present devices is around 150 °C, and the power conversion efficiency of the PSCs was significantly improved to 16.65% compared to that of the device without modification (14.05%). Such enhancement in efficiency is mainly attributed to the improved quality of perovskite films by improving the affinity of the SnO2 ETL, thus leading to better carrier transport and low charge recombination at the SnO2/perovskite interface. Moreover, the modified device by the DA SAM exhibited enhanced stability compared to the device without modification. Our results suggest that the introduction of the DA SAM on the ETL/perovskite interface is a promising method for highl...

Synergistic effect of anions and cations in additives for highly efficient and stable perovskite solar cells

Abstract: Organic–inorganic halide perovskites have attracted intensive attention due to their outstanding photophysical properties and high performance in optoelectronic devices. Moreover, the quality of perovskite films plays an important role in the performance of perovskite devices. The use of additives has been previously suggested as the simplest and effective method to improve the quality of perovskite films. However, only the cations or anions in most additives are capable of functioning as active species in improving the quality of perovskite films. Herein, we report that ammonium thiocyanate (NH4SCN) as an additive (contains NH4+ and SCN− ions) can significantly improve the quality of perovskite films as compared to NH4I and Pb(SCN)2 as additives containing the single active species of NH4+ and SCN−, respectively. The synergistic effect between the ions in NH4SCN is favorable for controlling the nucleation and growth speed of the crystal grains, which evidently increases the grain size and markedly improves the film stability. Finally, the efficiency of the device based on NH4SCN (16.47%) is significantly enhanced without a hysteresis effect as compared to that of the devices with single ions as the active species, e.g., NH4+ in NH4I (13.97%) and SCN− in Pb(SCN)2 (12.88%). Our findings suggest that the synergistic effect of anions and cations in additives is an effective strategy for realizing efficient and stable perovskites.

Recent Advances in Alternating Current‐Driven Organic Light‐Emitting Devices

Abstract: Organic light-emitting devices (OLEDs), typically operated with constant-voltage or direct-current (DC) power sources, are candidates for next-generation solid-state lighting and displays, as they are light, thin, inexpensive, and flexible. However, researchers have focused mainly on the device itself (e.g., development of novel materials, design of the device structure, and optical outcoupling engineering), and little attention has been paid to the driving mode. Recently, an alternative concept to DC-driven OLEDs by directly driving devices using time-dependent voltages or alternating current (AC) has been explored. Here, the effects of different device structures of AC-driven OLEDs, for example, double-insulation, single-insulation, double-injection, and tandem structure, on the device performance are systematically investigated. The formation of excitons and the dielectric layer, which are important to achieve high-performance AC-driven OLEDs, are carefully considered. The importance of gaining further understanding of the fundamental properties of AC-driven OLEDs is then discussed, especially as they relate to device physics.

An overview on enhancing the stability of lead halide perovskite quantum dots and their applications in phosphor-converted LEDs

Abstract: Beyond the unprecedented success achieved in photovoltaics (PVs), lead halide perovskites (LHPs) have shown great potential in other optoelectronic devices. Among them, nanometer-scale perovskite quantum dots (PQDs) with fascinating optical properties including high brightness, tunable emission wavelength, high color purity, and high defect tolerance have been regarded as promising alternative down-conversion materials in phosphor-converted light-emitting diodes (pc-LEDs) for lighting and next-generation of display technology. Despite the promising applications of perovskite materials in various fields, they have received strong criticism for the lack of stability. The poor stability has also attracted much attention. Within a few years, numerous strategies towards enhancing the stability have been developed. This review summarizes the mechanisms of intrinsic- and extrinsic-environment-induced decomposition of PQDs. Simultaneously, the strategies for improving the stability of PQDs are reviewed in detail, which can be classified into four types: (1) compositional engineering; (2) surface engineering; (3) matrix encapsulation; (4) device encapsulation. Finally, the challenges for applying PQDs in pc-LEDs are highlighted, and some possible solutions to improve the stability of PQDs together with suggestions for further improving the performance of pc-LEDs as well as the device lifetime are provided.

Perovskites for Next-Generation Optical Sources.

Abstract: Next-generation displays and lighting technologies require efficient optical sources that combine brightness, color purity, stability, substrate flexibility. Metal halide perovskites have potential use in a wide range of applications, for they possess excellent charge transport, bandgap tunability and, in the most promising recent optical source materials, intense and efficient luminescence. This review links metal halide perovskites' performance as efficient light emitters with their underlying materials electronic and photophysical attributes.

Metal-Doped Lead Halide Perovskites: Synthesis, Properties, and Optoelectronic Applications

Abstract: Doping of lead halide perovskites (LHPs) with the targeted impurities has emerged as an additional lever, a dimension beyond structural perfection and compositional distinction, for the alteration

Accelerated discovery of stable lead-free hybrid organic-inorganic perovskites via machine learning

Abstract: Rapidly discovering functional materials remains an open challenge because the traditional trial-and-error methods are usually inefficient especially when thousands of candidates are treated. Here, we develop a target-driven method to predict undiscovered hybrid organic-inorganic perovskites (HOIPs) for photovoltaics. This strategy, combining machine learning techniques and density functional theory calculations, aims to quickly screen the HOIPs based on bandgap and solve the problems of toxicity and poor environmental stability in HOIPs. Successfully, six orthorhombic lead-free HOIPs with proper bandgap for solar cells and room temperature thermal stability are screened out from 5158 unexplored HOIPs and two of them stand out with direct bandgaps in the visible region and excellent environmental stability. Essentially, a close structure-property relationship mapping the HOIPs bandgap is established. Our method can achieve high accuracy in a flash and be applicable to a broad class of functional material design.