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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Power conversion in SnS photocathodes made by electrochemical growth is limited by recombination at (002) buried facets

Herzenbergite α-SnS is a promising p-type semiconductor for photovoltaic and solar fuel applications, but current devices are plagued by substantial photovoltage losses. Here we use vibrating Kelvin probe surface photovoltage for the first time to study the recombination losses in microcrystalline SnS photoelectrodes. α-SnS films of varied crystal orientation, size, and shape are obtained by electrochemical growth from aqueous tin( II ) chloride and sodium thiosulfate solutions near room temperature. After application of a CdS passivation layer, the films function as photocathodes for the methylviologen reduction reaction. Photoelectrochemical and surface photovoltage measurements reveal that the performance of these devices is sensitively controlled by mainly the SnS crystal orientation and to a lesser extent by the grain size. For example, the highest charge recombination rates of 8.97 × 10 14 s −1 cm −2 and lowest photocurrent (0.73 mA cm −2 ) and lowest photovoltage (0.12 V) occur for SnS films containing 500 nm crystals with irregular shapes and SnS lattices tilted away from the (001) orientation. On the other hand, the best performance (1.62 mA cm −2 , 0.16 V, 3.32 × 10 12 s −1 cm −2 ) is seen for 1100 nm fully (001) oriented SnS nanoplates. Furthermore, these findings agree with improved charge carrier mobility in the 001 direction and they also show that charge recombination in SnS films occurs mainly at dangling Sn–S bonds at buried (002) facets. Such buried interfaces need to be suppressed for optimized solar energy conversion with SnS.

Najaf, Zainab [University of California, Davis, CA↗
DOE OSTI2023

Iodine Vacancies do not Cause Nonradiative Recombination in Halide Perovskites

The iodine vacancy (V I ) has frequently been discussed as a strong nonradiative recombination center in halide perovskites. This proposition was mainly based on the presence of charge-state transition levels in the band gap, as found in early first-principles calculations. In this work, we perform accurate hybrid-density-functional calculations for V I in CsPbI 3 , CsSnI 3 , and CsGeI 3 and find that V I does not have any transition levels in the band gap in CsPbI 3 , in contrast to the results from calculations based on semilocal functionals. The iodine vacancy V I does introduce levels in the band gap in CsSnI 3 and CsGeI 3 , but our explicitly computed nonradiative capture coefficients demonstrate that V I has a negligible impact on nonradiative recombination. Our study corrects a misunderstanding of the role of V I in the iodide-based perovskites, and shifts the focus toward identifying and mitigating actual recombination centers in order to further improve the optoelectronic performance.

14 SOLAR ENERGY↗
DOE OSTI2025

Langevin Dynamics modeling of gas-phase ion-ion recombination (Final Technical Report)

A self-consistent trajectory simulation approach to model MN reactions (Fig. 1) which incorporates the probability of electron transfer as a Monte Carlo operator (Fig. 2) was developed and published as Liu et al. J. Chem. Phys. 159, 114111 (2023). The electron transfer probability p ET estimated using the two-state Landau-Zener (LZ) theory was incorporated into classical trajectory simulations to elicit predictions of MN reaction cross-section σ (vacuum) or rate constant β (finite pressure). Electronic structure calculations with multireference configuration interaction (MRCI) and large correlation consistent basis sets were used to derive inputs to the LZ theory. The key advance of our trajectory simulation approach is the incorporation of electron transfer probability and the inclusion of the effect of ion-neutral interactions on MN using a Langevin representation of the effect of neutral gas on ions. For H + – H - and Li + – H(D) - pairs, our approach quantitatively agrees with measured speed-dependent cross-sections for up to ~10 5 m/s. For the ion pair Ne + – Cl - , our predictions of the MN rate constant at ~1 torr are a factor of ~2 – 3 higher than the experimentally measured value. Similarly, for Xe + – F - in the pressure range of ~20000 – 80000 Pa, our predictions of the MN rate constant are ~20% lower but are in excellent qualitative agreement with experimental data. The paradigm of using trajectory simulations to self-consistently model MN reactions is the basis for inclusion of additional non-classical, and static magnetic and electric field effects. Subsequent work, published as Roy et al. focused on modeling recombination rate constant for three ion pairs (rare gas Ar + cation and halide anions): Ar + – Cl - , Ar + – Br - , Ar + – I - , 2) considering spin-orbit couplings in the electronic structure calculations to obtain high-fidelity estimates of the electron transfer probability and incorporated within the classical trajectory simulations to elicit predictions. In addition to calculations of ion-ion recombination rate constants, a classical trajectory simulation technique (published as Roy et al. J. Chem. Phys. 162(9), 094104 (2023)) that uses quaternions to represent orientation of non-spherical particles (ions or aerosol particles) was developed to simulate the recombination of diatomic or more generally, polyatomic molecules. Finally, several other ion pairs such as Ne + – Cl - , Kr + – Cl - , were explored using the developed semi-classical trajectory simulations to understand various challenges in tackling electronic structure calculations. Using empirical approaches to parameterize the electron transfer radius, trajectory simulations were also used to probe the effect of ion number density on MN rate constant.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1972

The effect of secondary autoionization on dielectronic recombination.

Demonstration that, during the process of dielectronic recombination, the energy of a recombined ion after a resonance capture and subsequent stabilization may still be higher than the first ionization limit. If that happens, a secondary autoionization can take place and reduce the recombination coefficient. The importance of this effect is considered for iron ions Fe(9+) to Fe(13+).

Blaha, M.↗
NASA NTRS1972

Detection of interstellar recombination lines from emitters of intermediate mass.

The 18-cm microwave spectra of Orion B and W3A show evidence of an emission feature to the high-frequency side of the carbon recombination line. Observations at different frequencies establish that this feature results from electronic recombination. In addition, theoretical considerations, results of 21-cm observations, and computer-simulated spectra suggest that the new feature originates in a predominantly neutral hydrogen region and can be explained by a superposition of recombination lines from any or all of the following elements: Mg-24, Si-28, S-32, and Fe-56.

Chaisson, E. J.↗
NASA NTRS1972

Lifetime and quenching of CO /a super 3 pi/ produced by recombination of CO2 ions in a helium afterglow.

Demonstration that rapid dissociative recombination of CO2(+) in a flowing, helium afterglow is an efficient source of CO in the a super 3 pi metastable state. Ions produced by mixing CO2 with He(2 super 3 S) recombine to produce a CO metastable afterglow with a number density as great as 10 to the 9th per sq cm. Monitoring of the (a super 3 pi-X super 1 sigma) Cameron transition in CO was used to study the lifetime and quenching of CO (a super 3 pi) by CO2, N2, NO, and He. Recombination of CO2(+) also produces CO in the d super 3 delta and a' super 3 sigma states.

Wauchop, T. S.↗
NASA NTRS1973

Dissociative recombination of CH+ ions.

In recent studies of the formation of molecules in interstellar clouds, Solomon and Klemperer (1972) and Frisch (1972) were able to fit the observed ratios of CH+ and CH densities only with the assumption that the rate of dissociative recombination is extremely small. It is known that the rate for most diatomic molecules is relatively large, with the exception of H2+ and He2+ for which it is anomalously small. The present work explores the possibility that CH+ also has a low recombination rate. However, preliminary calculations yield a large rate of the dissociative recombination process, seemingly necessitating considerable revision of some recent models of interstellar clouds.

Bardsley, J. N.↗
NASA NTRS1976

Observations of heavy-element recombination lines in the Rho Ophiuchi dark cloud at 13 centimeters wavelength

High-sensitivity observations at the carbon 140-alpha and 141-alpha recombination-line frequencies in the direction of the Rho Oph dust cloud show the presence of recombination lines of carbon and sulfur, but not of other heavy elements. These results require that the elements Si, Fe, and Mg are depleted by factors greater than 15, 10, and 2, respectively, most likely into interstellar grains, whereas sulfur is undepleted. They also require that only approximately one-sixth of the carbon is present in the gas phase in the cloud. From the observed size of the C II region together with the observed carbon depletion, it is inferred that the density in the carbon-line-emitting region is 25,000 per cu cm and that the size of the S II region is significantly larger than that of the C II region. The agreement between the widths of the recombination lines (which arise in a small region of the cloud) and those of the more widely distributed molecular species suggests that the lines in this cloud are broadened by microturbulence on a scale of much less than 0.1 pc.

Knapp, G. R.↗
NASA NTRS1976

Determination of surface recombination velocity in heavily doped silicon

A method was developed and successfully tested for the determination of the effective surface recombination velocity of silicon layers doped by diffusion of phosphorus to a level of 10 to the 19th to 10 to the 21st per cu cm. The effective recombination velocity was obtained from the dependence of the electron-beam-induced current on the penetration of the electron beam of a scanning electron microscope. A special silicon diode was constructed which permitted the collection at the p-n junction of the carriers excited by the electron beam. This diode also permitted the study of the effects of surface preparation on the effective surface recombination velocity.

Watanabe, M.↗
NASA NTRS1977

Recombination lasing in a magnetoplasmadynamic arcjet

The plasmadynamic recombination laser concept is verified experimentally in a high power quasi-steady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4p to 4s Ar II transitions are established by collisional-radiative recombination of the Ar III ion. Using an optical cavity aligned transversely to the flow, recombination lasing of four such transitions, 5145, 4880, 4764 and 4727 A, is observed spectro-photographically and photoelectrically over the entire 1-msec discharge.

Campbell, E. M.↗
NASA NTRS1977

Recombination lasing in a magnetoplasmadynamic arcjet

The plasmadynamic recombination laser concept is verified experimentally in a high-power quasisteady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4p to 4s ArII transitions are established by collisional-radiative recombination of the ArIII ion. Using an optical cavity aligned transversely to the flow, recombination lasing of four such transitions, 5145, 4880, 4764, and 4727 A, is observed spectrophotographically and photoelectrically over the entire 1-msec discharge.

Campbell, E. M.↗
NASA NTRS1977

Determination of minority-carrier lifetime and surface recombination velocity with high spacial resolution

Quantitative analysis of the electron beam induced current in conjunction with high-resolution scanning makes it possible to evaluate the minority-carrier lifetime three dimensionally in the bulk and the surface recombination velocity two dimensionally, with a high spacial resolution. The analysis is based on the concept of the effective excitation strength of the carriers which takes into consideration all possible recombination sources. Two-dimensional mapping of the surface recombination velocity of phosphorus-diffused silicon diodes is presented as well as a three-dimensional mapping of the changes in the minority-carrier lifetime in ion-implanted silicon.

Watanabe, M.↗
NASA NTRS1977

Determination of the N2 recombination rate coefficient in the ionosphere

Measurements of aeronomic parameters made by the Atmosphere Explorer-C satellite are used to determine the recombination rate coefficient of N2(+) in the ionosphere. The rate is found to increase significantly with decreasing electron density. Values obtained range from approximately 1.4 x 10 to the -7th to 3.8 x 10 to the -7th cu cm/sec. This variation is explained in a preliminary way in terms of an increase in the rate coefficient with vibrational excitation. Thus, high electron densities depopulate high vibrational levels reducing the effective recombination rate, whereas, low electron densities result in an enhancement in the population of high vibrational levels, thus, increasing the effective recombination rate.

Orsini, N.↗
NASA NTRS1979

Dielectronic recombination rates, ionization equilibrium, and radiative energy-loss rates for neon, magnesium, and sulfur ions in low-density plasmas

Results of detailed and systematic calculations are presented for the total dielectronic recombination rate coefficients for the ions of Ne, Mg, and S in a low-density predominantly hydrogen plasma. The new recombination rates are used to calculate solar corona ionization-equilibrium distributions of the ions. The most important effect of dielectronic recombination for ions in corona equilibrium is found to be a shift in the maximum-abundance temperatures toward higher temperatures, which are in some cases reduced from those predicted on the basis of the simple Burgess formula.

Jacobs, V. L.↗
NASA NTRS1980

Recombination lasing in a magnetoplasmadynamic arcjet

The plasmadynamic recombination laser concept is verified experimentally in a high-power quasisteady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4p to 4s Ar II transitions are established by collisional-radiative recombination of the Ar III ion. Using an optical cavity aligned transversely to the flow, recombination lasing of seven such transitions, 5145, 4880, 4764, 4727, 4658, 4579, and 4545 A, is observed spectrophotographically and photoelectrically over the entire 1-msec discharge.

Campbell, E. M.↗
NASA NTRS1981

Collisional radiative recombination in high-pressure noble gas mixtures

Rate coefficients are calculated for neutral-assisted collisional radiative recombination in dense, weakly ionized rare-gas mixtures using the quasiequilibrium model developed by Bates. It is shown that the recombination rate can be significantly altered by the presence of a buffer gas. In particular, the presence of helium can enhance the collisional radiative recombination rate coefficient of heavy rare gases by a factor of 5.

Whitten, B. L.↗
NASA NTRS1981

Electron-temperature dependence of dissociative recombination of electrons with N2/+/.N2 dimer ions

The variation with electron temperature of the dissociative recombination of electrons with N2(+).N2 dimer ions is investigated in light of the importance of such ions in the lower ionosphere and in laser plasmas. Dissociative recombination coefficients were determined by means of a microwave afterglow mass spectrometer technique for electron temperatures from 300-5600 K and an ion and neutral temperature of 300 K. The recombination coefficient is found to be proportional to the -0.41 power of the electron temperature in this range, similar to that observed for the CO(+).CO dimer ion and consistent with the expected energy dependence for a fast dissociative process.

Whitaker, M.↗
NASA NTRS1981

Measurement of surface recombination velocity for silicon solar cells using a scanning electron microscope with pulsed beam

The role of surface recombination velocity in the design and fabrication of silicon solar cells is discussed. A scanning electron microscope with pulsed electron beam was used to measure this parameter of silicon surfaces. It is shown that the surface recombination velocity, s, increases by an order of magnitude when an etched surface degrades, probably as a result of environmental reaction. A textured front-surface-field cell with a high-low junction near the surface shows the effect of minority carrier reflection and an apparent reduction of s, whereas a tandem-junction cell shows an increasing s value. Electric fields at junction interfaces in front-surface-field and tandem-junction cells acting as minority carrier reflectors or sinks tend to alter the value of effective surface recombination velocity for different beam penetration depths. A range of values of s was calculated for different surfaces.

Daud, T.↗