Qingfeng Dong
University of Nebraska–Lincoln
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Featured researches published by Qingfeng Dong.
Science | 2015
Qingfeng Dong; Yanjun Fang; Yuchuan Shao; Padhraic Mulligan; Jie Qiu; Lei Cao; Jinsong Huang
Balanced carrier diffusion in perovskites The efficient operation of solar cells based on inorganic-organic perovskites requires balanced transport of positive and negative charge carriers over long distances. Dong et al. used a top-seeded solution growth method to obtain millimeter-scale single crystals of the organolead trihalide perovskite CH3NH3PbI3. Under low light illumination, the electron and hole diffusion lengths exceeded 3 mm, and under full sunlight illumination, they exceeded 175 µm. Science, this issue p. 967 Large perovskite crystals can exhibit long and balanced carrier diffusion lengths. Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3NH3PbI3 are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm−2) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. The long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.
Energy and Environmental Science | 2014
Zhengguo Xiao; Cheng Bi; Yuchuan Shao; Qingfeng Dong; Qi Wang; Yongbo Yuan; Chenggong Wang; Yongli Gao; Jinsong Huang
We report on an interdiffusion method to fabricate pin-hole free perovskite films using a low temperature (<105 °C) solution process. A high efficiency of 15.4%, with a fill factor of ∼80%, was achieved for the devices under one sun illumination. The interdiffusion method results in high device yield, with an efficiency of above 14.5% for more than 85% of the devices.
Energy and Environmental Science | 2017
Qi Wang; Bo Chen; Ye Liu; Yehao Deng; Yang Bai; Qingfeng Dong; Jinsong Huang
The stability of perovskite solar cells has shown a huge variation with respect to the film process and film morphology, while the underlining mechanism for the morphology-dependent degradation of the perovskite film has remained elusive. Herein, we report a scaling behavior of moisture-induced grain degradation in polycrystalline CH3NH3PbI3 films. The degradation rates of CH3NH3PbI3 films in moisture were shown to be sensitive to the grain sizes. The duration that was needed for different films to degrade by the same percent showed a linear relationship with the grain size, despite the fact that the films were formed by five different deposition methods. This scaling behavior can be explained by the degradation along the in-plane direction, which is initiated at the grain boundary (GB). The GBs of CH3NH3PbI3 films consist of an amorphous intergranular layer, which allows quick diffusion of moisture into the perovskite films. It was found that thermal annealing induced surface self-passivation plays a critical role in stabilizing the surfaces of thin films and single crystals by reducing the moisture-sensitive methylammonium ions at the surface. The determination of the scaling behavior of grain degradation highlights the importance of stabilizing the GBs to improve the stability of perovskite solar cells.
Physical Chemistry Chemical Physics | 2016
Jie Xing; Qi Wang; Qingfeng Dong; Yongbo Yuan; Yanjun Fang; Jinsong Huang
Understanding the influence of light on ion migration in organic-inorganic halide perovskite (OIHP) materials is important to understand the photostability of perovskite solar cells. We reveal that light could greatly reduce the ion migration energy barrier in both polycrystalline and single crystalline OIHP. The activation energies derived from conductivity measurement under 0.25 Sun decrease to less than one half of the values in the dark. A typical ion drift velocity in CH3NH3PbI3 polycrystalline films is 1.2 μm s-1 under 1 Sun, compared with 0.016 μm s-1 under 0.02 Sun. Ion migration across the photoactive layers in most OIHP devices thus takes only subseconds under 1 Sun illumination, which is much shorter than what it was thought to take. Most important of all, ion migration through a single crystal surface is still too slow to be observed even after illumination for two days due to the large ion diffusion activation energy, >0.38 eV.
Advanced Materials | 2014
Zhengguo Xiao; Qingfeng Dong; Cheng Bi; Yuchuan Shao; Yongbo Yuan; Jinsong Huang
Solvent-annealing is found to be an effective method to increase the grain size and carrier diffusion lengths of trihalide perovskite materials. The carrier diffusion length of MAPbI3 is increased to over 1 μm. The efficiency remains above 14.5% when the MAPbI3 thickness changes from 250 nm to 1 μm, with the highest efficiency reaching 15.6%.
Nature Materials | 2015
Zhengguo Xiao; Yongbo Yuan; Yuchuan Shao; Qi Wang; Qingfeng Dong; Cheng Bi; Pankaj Sharma; Alexei Gruverman; Jinsong Huang
Organolead trihalide perovskite (OTP) materials are emerging as naturally abundant materials for low-cost, solution-processed and highly efficient solar cells. Here, we show that, in OTP-based photovoltaic devices with vertical and lateral cell configurations, the photocurrent direction can be switched repeatedly by applying a small electric field of <1 V μm(-1). The switchable photocurrent, generally observed in devices based on ferroelectric materials, reached 20.1 mA cm(-2) under one sun illumination in OTP devices with a vertical architecture, which is four orders of magnitude larger than that measured in other ferroelectric photovoltaic devices. This field-switchable photovoltaic effect can be explained by the formation of reversible p-i-n structures induced by ion drift in the perovskite layer. The demonstration of switchable OTP photovoltaics and electric-field-manipulated doping paves the way for innovative solar cell designs and for the exploitation of OTP materials in electrically and optically readable memristors and circuits.
Energy and Environmental Science | 2014
Qi Wang; Yuchuan Shao; Qingfeng Dong; Zhengguo Xiao; Yongbo Yuan; Jinsong Huang
This work studied the influence of the methylammonium iodide/lead iodine precursor ratio on the perovskite film morphology and device performance. Using a non-stoichiometric precursor solution was demonstrated to be critical to form stoichiometric perovskite films. The compositions of the spun perovskite films were very sensitive to the surface of substrates, and can be very different from that in precursor solutions. Remarkably, we found that the unique double fullerene layers adopted could dramatically reduce dark current leakage by forming a Schottky junction with the anode, and effectively passivate traps in perovskite to increase the efficiency by boosting the fill factor to above 80% for perovskite solar cells.
Advanced Materials | 2015
Rui Dong; Yanjun Fang; Jungseok Chae; Jun Dai; Zhengguo Xiao; Qingfeng Dong; Yongbo Yuan; Andrea Centrone; Xiao Cheng Zeng; Jinsong Huang
Dr. R. Dong, Dr. Y. Fang, Z. Xiao, Dr. Q. Dong, Dr. Y. Yuan, Prof. X. C. Zeng, Prof. J. Huang Department of Mechanical and Materials Engineering University of Nebraska-Lincoln Lincoln , NE 68588 , USA E-mail: jhuang2@unl.edu Dr. J. Chae, Dr. A. Centrone Center for Nanoscale Science and Technology National Institute of Standards and Technology 100 Bureau Drive , Gaithersburg , MD 20899 , USA Dr. J. Chae Maryland Nanocenter University of Maryland College Park , MD 20742 , USA Dr. J. Dai, Prof. X. C. Zeng Department of Chemistry University of Nebraska-Lincoln Lincoln , NE 68588 , USA
Energy and Environmental Science | 2015
Yehao Deng; Edwin Peng; Yuchuan Shao; Zhengguo Xiao; Qingfeng Dong; Jinsong Huang
Organolead trihalide perovskites (OTPs) are nature abundant materials with prospects as future low-cost renewable energy sources boosted by the solution process capability of these materials. Here we report the fabrication of efficient OTP devices by a simple, high throughput and low-cost doctor-blade coating process which can be compatible with the roll-to-roll fabrication process for the large scale production of perovskite solar cell panels. The formulation of appropriate precursor inks by removing impurities is shown to be critical in the formation of continuous, pin-hole free and phase-pure perovskite films on large area substrates, which is assisted by a high deposition temperature to guide the nucleation and grain growth process. The domain size reached 80–250 μm in 1.5–2 μm thick bladed films. By controlling the stoichiometry and thickness of the OTP films, highest device efficiencies of 12.8% and 15.1% are achieved in the devices fabricated on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and cross-linked N4,N4′-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)–N4,N4′-diphenylbiphenyl-4,4′-diamine covered ITO substrates. Interestingly, the carrier diffusion length in doctor-bladed OTP films is beyond 3.5 μm which is significantly larger than in the spin-coated films, due to the formation of crystalline grains with a very large size by the doctor-blade coating method.
Energy and Environmental Science | 2016
Yuchuan Shao; Yanjun Fang; Tao Li; Qi Wang; Qingfeng Dong; Yehao Deng; Yongbo Yuan; Haotong Wei; Meiyu Wang; Alexei Gruverman; Jeffery Shield; Jinsong Huang
The efficiency of perovskite solar cells is approaching that of single-crystalline silicon solar cells despite the presence of a large grain boundary (GB) area in the polycrystalline thin films. Here, by using a combination of nanoscopic and macroscopic level measurements, we show that ion migration in polycrystalline perovskites dominates through GBs. Atomic force microscopy measurements reveal much stronger hysteresis both for photocurrent and dark-current at the GBs than on the grain interiors, which can be explained by faster ion migration at the GBs. The dramatically enhanced ion migration results in the redistribution of ions along the GBs after electric poling, in contrast to the intact grain area. The perovskite single-crystal devices without GBs show negligible current hysteresis and no ion-migration signal. The discovery of dominating ion migration through GBs in perovskites can lead to broad applications in many types of devices including photovoltaics, memristors, and ion batteries.