13 research outputs found
Acquiring and modeling of Si solar cell transient response to pulsed X-ray
We report on the acquisition and modeling of the transient response of a commercial silicon (Si) solar cell using a benchtop pulsed X-ray source. The solar-cell transient output to the X-ray pulses was acquired under the dark and steady-state light illumination to mimic the practical operation of a solar cell under different light illumination levels. A solar-cell circuit model was created to develop a fundamental understanding of the transient current/voltage response of solar cell at read-out circuit level. The model was validated by a good agreement between the simulation and experimental results. It was found that the solar-cell resistance ( R ) and capacitance ( C ) depend on the light illumination, and the resulting variation in RC time constant significantly affects the solar-cell transient response. Thus, the solar cell produced different transient signals under different illumination intensities in response to the same X-ray pulse. The experimental data acquired in this work proves the feasibility of using solar panels for prompt detection of nuclear detonations, which also builds a practical mode of X-ray detection using a low-cost self-powered detector
Designing Artificial Two-Dimensional Landscapes via Room-Temperature Atomic-Layer Substitution
Manipulating materials with atomic-scale precision is essential for the
development of next-generation material design toolbox. Tremendous efforts have
been made to advance the compositional, structural, and spatial accuracy of
material deposition and patterning. The family of 2D materials provides an
ideal platform to realize atomic-level material architectures. The wide and
rich physics of these materials have led to fabrication of heterostructures,
superlattices, and twisted structures with breakthrough discoveries and
applications. Here, we report a novel atomic-scale material design tool that
selectively breaks and forms chemical bonds of 2D materials at room
temperature, called atomic-layer substitution (ALS), through which we can
substitute the top layer chalcogen atoms within the 3-atom-thick
transition-metal dichalcogenides using arbitrary patterns. Flipping the layer
via transfer allows us to perform the same procedure on the other side,
yielding programmable in-plane multi-heterostructures with different
out-of-plane crystal symmetry and electric polarization. First-principle
calculations elucidate how the ALS process is overall exothermic in energy and
only has a small reaction barrier, facilitating the reaction to occur at room
temperature. Optical characterizations confirm the fidelity of this design
approach, while TEM shows the direct evidence of Janus structure and suggests
the atomic transition at the interface of designed heterostructure. Finally,
transport and Kelvin probe measurements on MoXY (X,Y=S,Se; X and Y
corresponding to the bottom and top layers) lateral multi-heterostructures
reveal the surface potential and dipole orientation of each region, and the
barrier height between them. Our approach for designing artificial 2D landscape
down to a single layer of atoms can lead to unique electronic, photonic and
mechanical properties previously not found in nature
Metallic surface doping of metal halide perovskites
Intentional doping is the core of semiconductor technologies to tune electrical and optical properties of semiconductors for electronic devices, however, it has shown to be a grand challenge for halide perovskites. Here, we show that some metal ions, such as silver, strontium, cerium ions, which exist in the precursors of halide perovskites as impurities, can n-dope the surface of perovskites from being intrinsic to metallic. The low solubility of these ions in halide perovskite crystals excludes the metal impurities to perovskite surfaces, leaving the interior of perovskite crystals intrinsic. Computation shows these metal ions introduce many electronic states close to the conduction band minimum of perovskites and induce n-doping, which is in striking contrast to passivating ions such as potassium and rubidium ion. The discovery of metallic surface doping of perovskites enables new device and material designs that combine the intrinsic interior and heavily doped surface of perovskites
Benign ferroelastic twin boundaries in halide perovskites for charge carrier transport and recombination
Grain boundaries have been established to impact charge transport, recombination and thus the power conversion efficiency of metal halide perovskite thin film solar cells. As a special category of grain boundaries, ferroelastic twin boundaries have been recently discovered to exist in both CH3NH3PbI3 thin films and single crystals. However, their impact on the carrier transport and recombination in perovskites remains unexplored. Here, using the scanning photocurrent microscopy, we find that twin boundaries have negligible influence on the carrier transport across them. Photoluminescence (PL) imaging and the spatial-resolved PL intensity and lifetime scanning confirm the electronically benign nature of the twin boundaries, in striking contrast to regular grain boundaries which block the carrier transport and behave as the non-radiative recombination centers. Finally, the twin-boundary areas are found still easier to degrade than grain interior
All-Solution-Processed Cu2ZnSnS4 Solar Cells with Self-Depleted Na2S Back Contact Modification Layer
The thinâfilm photovoltaic material Cu2ZnSnS4 (CZTS) has drawn worldwide attention in recent years due to its earthâabundant, nontoxic element constitution, and remarkable photovoltaic performance. Although stateâofâtheâart power conversion efficiency is achieved by hydrazineâbased methods, effort to fabricate such devices in a high throughput, environmentalâfriendly way is still highlydesired. Here a hydrazineâfree allâsolutionâprocessed CZTS solar cell with Na2S selfâdepleted back contact modification layer for the first time is demonstrated, using a ballâmilled CZTS as light absorber, lowâtemperature solutionâprocessed ZnO electronâtransport layer as well as silverânanowire transparent electrode. The inserting of Na2S selfâdepleted layer is proven to effectively stabilize the CZTS/Mo interface by eliminating a detrimental phase segregation reaction between CZTS and Moâcoated soda lime glass, thus leading to a better crystallinity of CZTS light absorbing layer, enhanced carrier transportation at CZTS/Mo interface as well as a smaller series resistance. Furthermore, the selfâdepletion feature of the Na2S modification layer also averts holeâtransportation barrier within the devices. The results show the vital importance of interfacial engineering for these CZST devices and the Na2S interface layer can be extended to other optoelectronic devices using Mo contact
Benign ferroelastic twin boundaries in halide perovskites for charge carrier transport and recombination
Grain boundaries have been established to impact charge transport, recombination and thus the power conversion efficiency of metal halide perovskite thin film solar cells. As a special category of grain boundaries, ferroelastic twin boundaries have been recently discovered to exist in both CH3NH3PbI3 thin films and single crystals. However, their impact on the carrier transport and recombination in perovskites remains unexplored. Here, using the scanning photocurrent microscopy, we find that twin boundaries have negligible influence on the carrier transport across them. Photoluminescence (PL) imaging and the spatial-resolved PL intensity and lifetime scanning confirm the electronically benign nature of the twin boundaries, in striking contrast to regular grain boundaries which block the carrier transport and behave as the non-radiative recombination centers. Finally, the twin-boundary areas are found still easier to degrade than grain interior
Working from Both Sides: Composite Metallic Semitransparent Top Electrode for High Performance Perovskite Solar Cells
We report herein perovskite solar
cells using solution-processed silver nanowires (AgNWs) as transparent
top electrode with markedly enhanced device performance, as well as
stability by evaporating an ultrathin transparent Au (UTA) layer beneath
the spin-coated AgNWs forming a composite transparent metallic electrode.
The interlayer serves as a physical separation sandwiched in between
the perovskite/hole transporting material (HTM) active layer and the
halide-reactive AgNWs top-electrode to prevent undesired electrode
degradation and simultaneously functions to significantly promote
ohmic contact. The as-fabricated semitransparent PSCs feature a <i>V</i><sub>oc</sub> of 0.96 V, a <i>J</i><sub>sc</sub> of 20.47 mA cm<sup>â2</sup>, with an overall PCE of over
11% when measured with front illumination and a <i>V</i><sub>oc</sub> of 0.92 V, a <i>J</i>sc of 14.29 mA cm<sup>â2</sup>, and an overall PCE of 7.53% with back illumination,
corresponding to approximately 70% of the value under normal illumination
conditions. The devices also demonstrate exceptional fabrication repeatability
and air stability
Bilateral alkylamine for suppressing charge recombination and improving stability in blade-coated perovskite solar cells
The power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) are already higher than that of other thin film technologies, but laboratory cell-fabrication methods are not scalable. Here, we report an additive strategy to enhance the efficiency and stability of PSCs made by scalable blading. Blade-coated PSCs incorporating bilateral alkylamine (BAA) additives achieve PCEs of 21.5 (aperture, 0.08 cm ) and 20.0% (aperture, 1.1 cm ), with a record-small open-circuit voltage deficit of 0.35 V under AM1.5G illumination. The stabilized PCE reaches 22.6% under 0.3 sun. Anchoring monolayer bilateral amino groups passivates the defects at the perovskite surface and enhances perovskite stability by exposing the linking hydrophobic alkyl chain. Grain boundaries are reinforced by BAA and are more resistant to mechanical bending and electron beam damage. BAA improves the device shelf lifetime to >1000 hours and operation stability to >500 hours under light, with 90% of the initial efficiency retained
High Efficiency Inverted Planar Perovskite Solar Cells with Solution-Processed NiO<sub><i>x</i></sub> Hole Contact
NiO<sub><i>x</i></sub> is a promising hole-transporting
material for perovskite solar cells due to its high hole mobility,
good stability, and easy processability. In this work, we employed
a simple solution-processed NiO<sub><i>x</i></sub> film
as the hole-transporting layer in perovskite solar cells. When the
thickness of the perovskite layer increased from 270 to 380 nm, the
light absorption and photogenerated carrier density were enhanced
and the transporting distance of electron and hole would also increase
at the same time, resulting in a large charge transfer resistance
and a long hole-extracted process in the device, characterized by
the UVâvis, photoluminescence, and electrochemical impedance
spectroscopy spectra. Combining both of these factors, an optimal
thickness of 334.2 nm was prepared with the perovskite precursor concentration
of 1.35 M. Moreover, the optimal device fabrication conditions were
further achieved by optimizing the thickness of NiO<sub><i>x</i></sub> hole-transporting layer and PCBM electron selective layer.
As a result, the best power conversion efficiency of 15.71% was obtained
with a <i>J</i><sub>sc</sub> of 20.51 mA·cm<sup>â2</sup>, a <i>V</i><sub>oc</sub> of 988 mV, and a FF of 77.51%
with almost no hysteresis. A stable efficiency of 15.10% was caught
at the maximum power point. This work provides a promising route to
achieve higher efficiency perovskite solar cells based on NiO or other
inorganic hole-transporting materials