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Laser-Tuned Large Photo Hall Effect in p-Type Silicon Based on Surface States
摘要： The photo Hall e?ect (PHE) has attracted much attention for a long time due to its broader application in photosensitive semiconductor devices. In this paper, we show a PHE observed in p-type silicon induced by pointolite irradiation, which di?ers from the conventional PHE caused by a surface light source. The Hall voltage is improved by 63 times when a laser is applied at the edge of the sample, and it presents good position-sensitive properties when the laser spot moves along the middle line of the sample. An ultra-broadband spectral responsivity is observed from 405 to 980 nm at 150?300 K. The experimental result shows that the laser-induced photo Hall voltage is not the simple superposition of photo current and dark current. Interestingly, this PHE can be greatly deteriorated when the surface state is destroyed and partially replaced by a Schottky barrier via covering with a thin Ag nano?lm. We attribute this phenomenon to the surface band bending caused by charged surface states. Compared with the traditional PHE, this laser-induced, position-sensitive, large-tuned-range e?ect based on surface states provides a di?erent approach to reveal the transmission properties of local unevenly distributed non-balanced carriers and can be used to design light-sensitive Hall devices.
关键词： photo Hall e?ect,surface states,recombination rate,magnetic ?eld,Schottky barrier
更新于2025-09-19 17:13:59
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Surface modification of TiO2 photoanodes with In3+ using a simple soaking technique for enhancing the efficiency of dye-sensitized solar cells
摘要： Indium-doped TiO2 photoanode for dye-sensitized solar cells are prepared using a simple surface-doping technique by soaking the TiO2 film in acidic In3+ solution at 70oC for 30, 45 and 60 minutes followed by sintering at 450oC. Structural characterization of In-doped TiO2 films by SEM, TEM, EDX, XRD and Raman spectroscopy revealed the successful attachment of Indium to the surface of TiO2 and that the amount of In dopant is proportional to the soaking time. The PCE of the devices fabricated from In-doped TiO2 with a soaking time of 30 minutes produced an increase of 18.0 % compared to the undoped cells. Charge extraction analysis at open-circuit revealed that surface-doping with indium shifts TiO2 band edge downward. However, the increase in VOC was found as the net effect of negative movement of CB and retarded recombination caused by TiO2 surface passivation via the In dopant.
关键词： Recombination reactions,Surface-doping,Photovoltage decay,X-ray spectroscopy
更新于2025-09-19 17:13:59
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Two-Dimensional Bi <sub/>2</sub> O <sub/>2</sub> Se with High Mobility for High-Performance Polymer Solar Cells
摘要： Carrier mobility is a critical factor for power conversion efficiency (PCE) of polymer solar cells (PSCs), and the low charge carrier mobility still limits performance improvement of PSCs. Adding high mobility material into the active layer is one of the better ways to enhance the PCE of PSCs. Two-dimensional (2D) Bi2O2Se can be an ideal additive material for improving the carrier mobility of PSCs because its ultrahigh mobility and high thermal stability. In this work, the Bi2O2Se few-layer 2D nanoflakes are fabricated by combining lithium intercalation with shear force-assisted liquid phase exfoliation and applied as an additive to promote charge transport in PSCs for the first time. The 2D Bi2O2Se nanoflakes, when introduced into the active layer, not only provide new interface between donor and acceptor and efficient charge transfer pathways but also induce crystallization of photosensitive layer and form the continuous interpenetrating networks, which promotes the exciton separation and charge transfer in photosensitive layer. As a result, the PCE of device based on PBDB-T:ITIC is increased from 10.09% (0 wt%) to 12.22% (2 wt%). Meanwhile, the PCE of device based on PM6:Y6 is also increased from 14.59% for binary device to 16.28% for optimized ternary device (2 wt%). Moreover, the optimized ternary device shows excellent air stability by suppressing the mixing of the two phases. This work supplies a good method to enhance the PCE of PSCs, also shows the Bi2O2Se material has a good prospect in photovoltaic devices.
关键词： crystallinity,charge recombination,Polymer solar cells,stability,carrier mobility,2D Bi2O2Se flakes
更新于2025-09-19 17:13:59
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Impact of intentional photo-oxidation of a donor polymer and PC <sub/>70</sub> BM on solar cell performance
摘要： Impact of intentional photo-oxidation of a donor polymer and PC70BM on solar cell performance. A short lifetime is the main factor hindering the wider implementation of low-cost organic photovoltaics through non-ideal encapsulation layers is a known cause of degradation for polymer/fullerene based solar cells. To better understand the origin of this performance degradation, we study the effect of intentional exposure of the photo-active layer to simulated sunlight (AM1.5) in air both on the solar cell performance and on the molecular semiconductor materials. Cathode-free thin films of a blend of the electron donor polymer poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and the electron acceptor fullerene derivative [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM) were exposed to simulated sunlight in air. Fourier-transform infrared spectra demonstrate the formation of carbonyl photo-oxidation products in the blend films, as well as in the pristine polymer and fullerene films. Solar cells prepared with photo-oxidized active layers show increasingly degraded electrical performance (lower short circuit current, open circuit voltage and fill factor) with increasing exposure time. The increased diode ideality factor indicates that trap-assisted recombination hinders device operation after exposure. The external quantum efficiency decreases drastically with increasing exposure time over the whole photon energy range, while the UV-vis absorption spectra of the blend films only show a mild photo-induced bleaching. This demonstrates that not only the photo-induced degradation of the solar cell performance is not predominantly caused by the loss in light absorption, but charge transport and collection are also hampered. This is explained by the fact that photo-oxidation of PC70BM causes bonds in its conjugated cage to break, as evidenced by the decreased p* intensity in C1s-NEXAFS spectra of PC70BM films. This degradation of unoccupied states of PC70BM will hinder the transport of photo-generated electrons to the electrode. Surface photovoltage spectroscopy gives direct evidence for gap states at the surface of a PC70BM film, formed after 2 hours of exposure and resulting in upward band bending at the PC70BM/air surface. These observations indicate that the photo-oxidation of PC70BM is likely to be the main cause of the performance degradation observed when the photoactive layer of a TQ1:PC70BM solar cell is intentionally exposed to light in air.
关键词： polymer/fullerene solar cells,photo-oxidation,organic photovoltaics,PC70BM,degradation,trap-assisted recombination,charge transport,TQ1
更新于2025-09-19 17:13:59
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Real-Time Detection of Single Auger Recombination Events in a Self-Assembled Quantum Dot
摘要： Auger recombination is a non-radiative process, where the recombination energy of an electron-hole pair is transferred to a third charge carrier. It is a common effect in colloidal quantum dots that quenches the radiative emission with an Auger recombination time below nanoseconds. In self-assembled QDs, the Auger recombination has been observed with a much longer recombination time in the order of microseconds. Here, we use two-color laser excitation on the exciton and trion transition in resonance fluorescence on a single self-assembled quantum dot to monitor in real-time single quantum events of the Auger process. Full counting statistics on the random telegraph signal give access to the cumulants and demonstrate the tunability of the Fano factor from a Poissonian to a sub-Poissonian distribution by Auger-mediated electron emission from the dot. Therefore, the Auger process can be used to tune optically the charge carrier occupation of the dot by the incident laser intensity; independently from the electron tunneling from the reservoir by the gate voltage. Our findings are not only highly relevant for the understanding of the Auger process, it also demonstrates the perspective of the Auger effect for controlling precisely the charge state in a quantum system by optical means.
关键词： Auger recombination,Resonance fluorescence,Quantum dots,Full counting statistics,Random telegraph signal
更新于2025-09-19 17:13:59
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Double-Mesoscopic Hole-Transport-Material-Free Perovskite Solar Cells: Overcoming Charge-Transport Limitation by Sputtered Ultra-Thin Al <sub/>2</sub> O <sub/>3</sub> Isolating Layer
摘要： The electrically insulating space layer takes a fundamental role in monolithic carbon-graphite based perovskite solar cells (PSCs) and it has been established to prevent the charge recombination of electrons at the mp-TiO2/carbon-graphite (CG) interface. Thick 1 μm printed layers are commonly used for this purpose in the established triple-mesoscopic structures to avoid ohmic shunts and to achieve a high open circuit voltage. In this work, we have developed a reproducible large-area procedure to replace this thick space layer with an ultra-thin dense 40 nm sputtered Al2O3 which acts as highly electrically insulating layer preventing ohmic shunts. Herewith, transport limitations related so far to the hole diffusion path length inside the thick mesoporous space layer have been omitted by concept. This will pave the way towards the development of next generation double-mesoscopic carbon-graphite based PSCs with highest efficiencies. Scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX) and atomic force microscopy (AFM) measurements show the presence of fully oxidized sputtered Al2O3 layer forming a pseudo-porous covering of the underlying mesoporous layer. The thickness has been finely tuned for the achievement of both electrical isolation and optimal infiltration of the perovskite solution allowing full percolation and crystallization. Photo voltage decay, light-dependent and time-dependent photoluminescence measurements showed that the optimal 40 nm thick Al2O3 not only prevents ohmic shunts but also efficiently reduces the charge recombination at the mp-TiO2/CG interface and, at the same time, allows efficient hole diffusion through the perovskite crystals embedded in its pseudo-pores. Thus, stable VOC of 1 V using CH3NH3PbI3 perovskite has been achieved under full sun AM 1.5 G with stabilized device performance of 12.1%.
关键词： Perovskite solar cells,Al2O3 Space layer,Double-mesoscopic,Carbon-graphite,HTM-free,Sputtering,Interface recombination
更新于2025-09-19 17:13:59
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Built-in voltage enhanced by in-situ electrochemical polymerized undoped conjugated hole-transporting modifier in organic solar cells
摘要： Herein, a new electropolymerized (EP) film named poly-triphenylcarbazole fluoranthene (p-TPCF) has been in-situ synthesized by electrochemical cyclic voltammetry method, and applied to tune the work-function (WF) of the PEDOT:PSS hole-transporting layer (HTL) in organic solar cells (OSCs). Multi techniques, including Kelvin probe force microscopy (KPFM), light intensity dependent solar cell characterization, Mott-Schottky analysis, transient photovoltage (TPV) and transient photocurrent (TPC) measurements, have been explored to provide insights into the mechanism. Benefiting from deeper work-function (WF), larger built-in voltage (Vbi), decreased recombination, longer carrier lifetime, the devices with EP film exhibited superior device performance with simultaneously enhanced Voc, Jsc and FF.
关键词： PEDOT:PSS,built-in voltage,work-function tuning,organic solar cells,carrier lifetime,electropolymerized film,charge recombination
更新于2025-09-19 17:13:59
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Reduced-dimensional perovskite photovoltaics with homogeneous energy landscape
摘要： Reduced-dimensional (quasi-2D) perovskite materials are widely applied for perovskite photovoltaics due to their remarkable environmental stability. However, their device performance still lags far behind traditional three dimensional perovskites, particularly high open circuit voltage (Voc) loss. Here, inhomogeneous energy landscape is pointed out to be the sole reason, which introduces extra energy loss, creates band tail states and inhibits minority carrier transport. We thus propose to form homogeneous energy landscape to overcome the problem. A synergistic approach is conceived, by taking advantage of material structure and crystallization kinetic engineering. Accordingly, with the help of density functional theory guided material design, (aminomethyl) piperidinium quasi-2D perovskites are selected. The lowest energy distribution and homogeneous energy landscape are achieved through carefully regulating their crystallization kinetics. We conclude that homogeneous energy landscape significantly reduces the Shockley-Read-Hall recombination and suppresses the quasi-Fermi level splitting, which is crucial to achieve high Voc.
关键词： homogeneous energy landscape,open circuit voltage loss,Reduced-dimensional perovskite,photovoltaics,Shockley-Read-Hall recombination
更新于2025-09-19 17:13:59
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Upper limit to the photovoltaic efficiency of imperfect crystals from first principles
摘要： The Shockley-Queisser (SQ) limit provides a convenient metric for predicting light-to-electricity conversion efficiency of a solar cell based on the band gap of the light-absorbing layer. In reality, few materials approach this radiative limit. We develop a formalism and computational method to predict the maximum photovoltaic efficiency of imperfect crystals from first principles. The trap-limited conversion efficiency includes equilibrium populations of native defects, their carrier-capture coefficients, and the associated recombination rates. When applied to kesterite solar cells, we reveal an intrinsic limit of 20% for Cu2ZnSnSe4, which falls far below the SQ limit of 32%. The effects of atomic substitution and extrinsic doping are studied, leading to pathways for an enhanced efficiency of 31%. This approach can be applied to support targeted-materials selection for future solar-energy technologies.
关键词： recombination rates,kesterite solar cells,Shockley-Queisser limit,native defects,carrier-capture coefficients,photovoltaic efficiency
更新于2025-09-19 17:13:59
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Improving Performance of Non-fullerene Organic Solar Cells over 13% by Employing Silver Nanowires Doped PEDOT:PSS Composite Interface
摘要： Ag NWs/PEDOT:PSS composite was prepared by a facile solution-processing method, and was employed as anode interface in non-fullerene organic solar cells (OSCs). With the presence of Ag NWs (5%, v/v%)/PEDOT:PSS interfacial layer, a high power conversion efficiency (PCE) up to 13.53% was achieved based on PBDB-T-2Cl:IT-4F photoactive layer system, much higher than the efficiency of the controlled counterpart device with pristine PEDOT:PSS as anode modifier. Simultaneous enhancements in short-circuit current and fill factor were observed, in comparison to the case of pristine PEDOT:PSS interface, due to the improved electrical conductivity of Ag NWs/PEDOT:PSS composites accompanied by the increased work function for a better matching with ITO counter electrode, which facilitated the increased charge transmission, and the reduced charge recombination at the anode/photoactive interface for the improved device performance. The results clearly revealed that Ag NWs/PEDOT:PSS composite interface is beneficial to improve the charge extraction and in favor of realizing highly efficient non-fullerene OSCs.
关键词： composite interface,electrical conductivity,Ag nanowires,recombination,Non-fullerene organic solar cells
更新于2025-09-19 17:13:59