Benjamin Ecker

Bio: Benjamin Ecker is an academic researcher from University of Rochester. The author has contributed to research in topics: Perovskite (structure) & X-ray photoelectron spectroscopy. The author has an hindex of 7, co-authored 11 publications receiving 1032 citations.

Sensitive X-ray detectors made of methylammonium lead tribromide perovskite single crystals

Abstract: Single-crystal perovskite devices 2–3 mm thick exhibit 16.4% X-ray detection efficiency with sensitivity four times higher than α-Se X-ray detectors.

Reducing Surface Halide Deficiency for Efficient and Stable Iodide-Based Perovskite Solar Cells.

Abstract: State-of-the-art, high-performance perovskite solar cells (PSCs) contain a large amount of iodine to realize smaller bandgaps. However, the presence of numerous iodine vacancies at the surface of the film formed by their evaporation during the thermal annealing process has been broadly shown to induce deep-level defects, incur nonradiative charge recombination, and induce photocurrent hysteresis, all of which limit the efficiency and stability of PSCs. In this work, modifying the defective surface of perovskite films with cadmium iodide (CdI2) effectively reduces the degree of surface iodine deficiency and stabilizes iodine ions via the formation of strong Cd-I ionic bonds. This largely reduces the interfacial charge recombination loss, yielding a high efficiency of 21.9% for blade-coated PSCs with an open-circuit voltage of 1.20 V, corresponding to a record small voltage deficit of 0.31 V. The CdI2 surface treatment also improves the operational stability of the PSCs, retaining 92% efficiency after constant illumination at 1 sun intensity for 1000 h. This work provides a promising strategy to optimize the surface/interface optoelectronic properties of perovskites for more efficient and stable solar cells and other optoelectronic devices.

Argon Plasma Treatment to Tune Perovskite Surface Composition for High Efficiency Solar Cells and Fast Photodetectors.

Abstract: The surface composition of perovskite films is very sensitive to film processing and can deviate from the optimal, which generates unfavorable defects and results in efficiency loss in solar cells and slow response speed in photodetectors. An argon plasma treatment is introduced to modify the surface composition by tuning the ratio of organic and inorganic components as well as defect type before deposition of the passivating layer. It can efficiently enhance the charge collection across the perovskite-electrode interface by suppressing charge recombination. Therefore, perovskite solar cells with argon plasma treatment yield enhanced efficiency to 20.4% and perovskite photodetectors can reach their fastest respond speed, which is solely limited by the carrier mobility.

Environmental Surface Stability of the MAPbBr3 Single Crystal

Abstract: Organic–inorganic halide perovskites have emerged as a promising semiconductor family because of their remarkable performance in optoelectronic devices. On the other hand, the stability of perovskites remains a critical issue. In this work, we report a quantitative and systematic investigation of in situ cleaved MAPbBr3 single-crystal degradation processes in X-ray, N2, O2, and H2O environments. The high-quality crystals were monitored by high-resolution X-ray photoelectron spectroscopy with careful control of the exposure time and pressure. The detailed electronic structure and compositional changes of the crystal were tracked throughout the different exposures, and these studies provided insights into the various degradation mechanisms. We identified that ∼10% of the surface MAPbBr3 degraded to metallic lead under X-rays in vacuum, while N2 could protect the sample from the degradation for 9 h under the same condition. Other measurements showed that while the surface was not sensitive to pure O2, it was...

Valence band dispersion measurements of perovskite single crystals using angle-resolved photoemission spectroscopy

Abstract: The electronic structure of a cleaved perovskite (CH3NH3PbBr3) single crystal was studied in an ultra-high vacuum (UHV) system using angle-resolved photoemission spectroscopy (ARPES) and inverse photoelectron spectroscopy (IPES). Highly reproducible dispersive features of the valence bands were observed with symmetry about the Brillouin zone center and boundaries. The largest dispersion width was found to be ∼0.73 eV and ∼0.98 eV along the ΓX and ΓM directions, respectively. The effective mass of the holes was estimated to be ∼0.59m0. The quality of the surface was verified using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The elemental composition was investigated using high resolution X-ray photoelectron spectroscopy (XPS). The experimental electronic structure shows a good agreement with the theoretical calculation.

All-inorganic perovskite nanocrystal scintillators

Abstract: The rising demand for radiation detection materials in many applications has led to extensive research on scintillators1–3. The ability of a scintillator to absorb high-energy (kiloelectronvolt-scale) X-ray photons and convert the absorbed energy into low-energy visible photons is critical for applications in radiation exposure monitoring, security inspection, X-ray astronomy and medical radiography4,5. However, conventional scintillators are generally synthesized by crystallization at a high temperature and their radioluminescence is difficult to tune across the visible spectrum. Here we describe experimental investigations of a series of all-inorganic perovskite nanocrystals comprising caesium and lead atoms and their response to X-ray irradiation. These nanocrystal scintillators exhibit strong X-ray absorption and intense radioluminescence at visible wavelengths. Unlike bulk inorganic scintillators, these perovskite nanomaterials are solution-processable at a relatively low temperature and can generate X-ray-induced emissions that are easily tunable across the visible spectrum by tailoring the anionic component of colloidal precursors during their synthesis. These features allow the fabrication of flexible and highly sensitive X-ray detectors with a detection limit of 13 nanograys per second, which is about 400 times lower than typical medical imaging doses. We show that these colour-tunable perovskite nanocrystal scintillators can provide a convenient visualization tool for X-ray radiography, as the associated image can be directly recorded by standard digital cameras. We also demonstrate their direct integration with commercial flat-panel imagers and their utility in examining electronic circuit boards under low-dose X-ray illumination. All-inorganic perovskite nanocrystals containing caesium and lead provide low-cost, flexible and solution-processable scintillators that are highly sensitive to X-ray irradiation and emit radioluminescence that is colour-tunable across the visible spectrum.

High efficiency planar-type perovskite solar cells with negligible hysteresis using EDTA-complexed SnO2

Abstract: Even though the mesoporous-type perovskite solar cell (PSC) is known for high efficiency, its planar-type counterpart exhibits lower efficiency and hysteretic response. Herein, we report success in suppressing hysteresis and record efficiency for planar-type devices using EDTA-complexed tin oxide (SnO2) electron-transport layer. The Fermi level of EDTA-complexed SnO2 is better matched with the conduction band of perovskite, leading to high open-circuit voltage. Its electron mobility is about three times larger than that of the SnO2. The record power conversion efficiency of planar-type PSCs with EDTA-complexed SnO2 increases to 21.60% (certified at 21.52% by Newport) with negligible hysteresis. Meanwhile, the low-temperature processed EDTA-complexed SnO2 enables 18.28% efficiency for a flexible device. Moreover, the unsealed PSCs with EDTA-complexed SnO2 degrade only by 8% exposed in an ambient atmosphere after 2880 h, and only by 14% after 120 h under irradiation at 100 mW cm−2. The development of high efficiency planar-type perovskite solar cell has been lagging behind the mesoporous-type counterpart. Here Yang et al. modify the oxide based electron transporting layer with organic acid and obtain planar-type cells with high certified efficiency of 21.5% and decent stability.

Solution-processed semiconductors for next-generation photodetectors

Abstract: Efficient light detection is central to modern science and technology. Current photodetectors mainly use photodiodes based on crystalline inorganic elemental semiconductors, such as silicon, or compounds such as III–V semiconductors. Photodetectors made of solution-processed semiconductors — which include organic materials, metal-halide perovskites and quantum dots — have recently emerged as candidates for next-generation light sensing. They combine ease of processing, tailorable optoelectronic properties, facile integration with complementary metal–oxide–semiconductors, compatibility with flexible substrates and good performance. Here, we review the recent advances and the open challenges in the field of solution-processed photodetectors, examining the topic from both the materials and the device perspective and highlighting the potential of the synergistic combination of materials and device engineering. We explore hybrid phototransistors and their potential to overcome trade-offs in noise, gain and speed, as well as the rapid advances in metal-halide perovskite photodiodes and their recent application in narrowband filterless photodetection. Conventional photodetectors, made of crystalline inorganic semiconductors, are limited in terms of the compactness and sensitivity they can reach. Photodetectors based on solution-processed semiconductors combine ease of processing, tailorable optoelectronic properties and good performance, and thus hold potential for next-generation light sensing.

Grain boundary dominated ion migration in polycrystalline organic–inorganic halide perovskite films

Abstract: 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.

Understanding the physical properties of hybrid perovskites for photovoltaic applications

Abstract: This Review summarizes advances in understanding the unique physical properties of hybrid perovskites that enable the fabrication of high-efficiency solar cells with high open-circuit voltages, which is crucial for their further development towards commercialization.