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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Reducing Surface Recombination Velocity of Methylammonium-Free Mixed-Cation Mixed-Halide Perovskites via Surface Passivation

We control surface recombination in the mixed-cation, mixed-halide perovskite, FA0.83Cs0.17Pb(I0.85Br0.15)3, by passivating nonradiative defects with the polymerizable Lewis base (3-aminopropyl)trimethoxysilane (APTMS). We demonstrate average minority carrier lifetimes >4 µs, nearly single exponential monomolecular photoluminescence decays, and high external photoluminescence quantum efficiencies (>20%, corresponding to ~97% of the maximum theoretical quasi-Fermi-level splitting) at low excitation fluence. We confirm both the composition and valence band edge position of the FA0.83Cs0.17Pb(I0.85Br0.15)3 perovskite using multi-institutional, cross-validated, X-ray photoelectron spectroscopy and UV photoelectron spectroscopy measurements. We extend the APTMS surface passivation to higher bandgap double-cation (FA and Cs) compositions (1.7, 1.75, and 1.8 eV) as well as the widely used triple-cation (FA, MA, and Cs) composition. Finally, we demonstrate that the average surface recombination velocity decreases from ~1000 to ~10 cm/s post APTMS passivation for FA0.83Cs0.17Pb(I0.85Br0.15)3. Our results demonstrate that surface-mediated recombination is the primary nonradiative loss pathway in many methylammonium (MA)-free mixed-cation mixed-halide films with a range of different bandgaps, which is a problem observed for a wide range of perovskite active layers and reactive electrical contacts. Our study also provides insights to develop passivating molecules that help reduce surface recombination in MA-free mixed-cation mixed-halide films and indicates that surface passivation and contact engineering will enable near-theoretical device efficiencies with these materials.

14 SOLAR ENERGY↗
NASA NTRS1985

Steady-state currents in p-n junction filaments or grains in case of large surface recombination velocities at lateral surfaces

Recently it has been pointed out that the saturation current of a semiconductor filament which constitutes part of a p-n junction diverges when the surface recombination velocity at the faces become infinitely large. Here it is pointed out that this is to be expected on physical grounds since, whenever the carrier concentration is kept off equilibrium by an outside agent, and at the same time recombination lifetimes in the bulk or in surface layers tend to zero, concentration gradients tend to infinity. As also previously noted, the situation can be remedied by using realistic (finite) surface recombination velocities in model calculations. However, this procedure leads to mathematical complexities which have been circumvented recently by the introduction of a heuristic approach. It is the aim of this paper to assess the validity of the heuristic approach by means of detailed and exact calculations.

Von Roos, O.↗
DOE OSTI2022

(3-Aminopropyl)trimethoxysilane Surface Passivation Improves Perovskite Solar Cell Performance by Reducing Surface Recombination Velocity

We demonstrate reduced surface recombination velocity (SRV) and enhanced power-conversion efficiency (PCE) in mixed-cation mixed-halide perovskite solar cells by using (3-aminopropyl)trimethoxysilane (APTMS) as a surface passivator. We show the APTMS serves to passivate defects at the perovskite surface, while also decoupling the perovskite from detrimental interactions at the C 60 interface. We measure a SRV of ~125 ± 14 cm/s, and a concomitant increase of ~100 meV in quasi-Fermi level splitting in passivated devices compared to the controls. We use time-resolved photoluminescence and excitation-correlation photoluminescence spectroscopy to show that APTMS passivation effectively suppresses non-radiative recombination. We show that APTMS improves both the fill factor and open-circuit voltage (V OC ), increasing V OC from 1.03 V for control devices to 1.09 V for APTMS-passivated devices, and leads to a PCE increase from 15.90% to 18.03%. Here, we attribute the enhanced performance to reduced defect density resulting in suppressed nonradiative recombination and lower SRV at the perovskite/transport layer interface.

14 SOLAR ENERGY↗
DOE OSTI2020

Passivated Interfaces and Surface Recombination Velocities in Halide Perovskites

Surfaces and charge-extracting contacts remain major sources of non-radiative recombination loss; limiting the performance of perovskite PV compared to theoretical limits. We investigate mixed-cation mixed-halide perovskites and demonstrate that, with chemical surface passivation, they can achieve >4 μs minority carrier lifetimes, and >20% external PL quantum yields (PLQY), and nearly single-exponential decay kinetics. This high PLQY observed corresponds to ~97% of the Shockley-Queisser theoretical quasi-fermi level splitting, a first for MA-free mixed-cation mixed-halide compositions. The high PLQY and long PL lifetimes allow us to measure average surface recombination velocities (SRV) <10cm/s, with a champion low of ~1cm/s (a conservative estimate). We show how such improvements in SRV should lead to an absolute improvement in PCE of >4% even with the best of contact alignments. We investigate different MA-free high bandgap compositions, including bandgaps relevant for tandem applications (1.7-1.8eV), and demonstrate performance improvements across all these compositions with our surface passivation strategy. Lastly, using a combination of surface characterization techniques, we show Lewis base interactions of the passivating agent with the perovskite surfaces.

passivation↗
NASA NTRS1990

Measurement of surface recombination velocity on heavily doped indium phosphide

Surface recombination velocity (SRV) on heavily doped n-type and p-type InP was measured as a function of surface treatment. For the limited range of substrates and surface treatments studied, SRV and surface stability depend strongly on the surface treatment. SRVs of 100,000 cm/sec in both p-type and n-type InP are obtainable, but in n-type the low-SRV surfaces were unstable, and the only stable surfaces on n-type had SRVs of more than 10to the 6th cm/sec.

Jenkins, Phillip↗
DOE OSTI2020

Passivated Interfaces and Surface Recombination Velocities in Halide Perovskites

Surfaces and charge-extracting contacts remain major sources of non-radiative recombination loss; limiting the performance of perovskite PV compared to theoretical limits. We investigate mixed-cation mixed-halide perovskites and demonstrate that, with chemical surface passivation, they can achieve >4 μs minority carrier lifetimes, and >20% external PL quantum yields (PLQY), and nearly single-exponential decay kinetics. This high PLQY observed corresponds to ~97% of the Shockley-Queisser theoretical quasi-fermi level splitting, a first for MA-free mixed-cation mixed-halide compositions. The high PLQY and long PL lifetimes allow us to measure average surface recombination velocities (SRV) <10cm/s, with a champion low of ~1cm/s (a conservative estimate). We show how such improvements in SRV should lead to an absolute improvement in PCE of >4% even with the best of contact alignments. We investigate different MA-free high bandgap compositions, including bandgaps relevant for tandem applications (1.7-1.8eV), and demonstrate performance improvements across all these compositions with our surface passivation strategy. Lastly, using a combination of surface characterization techniques, we show Lewis base interactions of the passivating agent with the perovskite surfaces.

14 SOLAR ENERGY↗
NASA NTRS1990

Surface recombination velocity and lifetime in InP measured by transient microwave reflectance

Minority carrier lifetime and surface recombination velocity are determined in organometallic vapor-phase epitaxy (OMVPE)-grown InP by a contactless microwave technique. For lightly doped n-type InP, a surface recombination velocity of 5000 cm/s is measured. However, in solar cells with a heavily doped n-type emitter a surface recombination velocity of 1 x 10 to the 6th cm/s is observed. Possible reasons for this due to surface pinning are discussed. The effects of various chemical treatments and SiO on the surface recombination velocity are measured.

Bothra, S.↗
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.↗
NASA NTRS1981

Surface recombination velocity measurement for silicon solar cells

For the design and fabrication of silicon solar cells approaching theoretical ultimate conversion efficiencies, surface recombination velocity plays a crucial role. A technique using a scanning electron microscope with pulsed electron beam has been developed for thy measurement of this important parameter for silicon surfaces. It is shown that the surface recombination velocity(s) increases by an order of magnitude when a freshly etched sample is left out for a few hours, presumably due to generation of surface states. A textured front surface field (FSF) 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 (TJ) cell with n+-p junction near the surface gives larger s value.

Daud, T.↗
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

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 NTRS1991

Evaluation of the minority carrier diffusion length and surface-recombination velocity in GaAs p/n solar cells

The minority carrier diffusion length (Lp) and the surface recombination velocity (Vs) were measured as a function of distance (x) from the p-n junction in GaAs p/n concentrator solar cells. The measured Vs values were used in a theoretical expression for the normalized electron-beam-induced current. A fitting procedure was then used to fit this expression with experimental values to obtain Lp. The results show that both Vs and Lp vary with x. Lp measured in irradiated cells showed a marked reduction. These values were compared to those measured previously which did not account for Vs.

Hakimzadeh, Roshanak↗
NASA NTRS1985

Quantification of the effects of generation volume, surface recombination velocity, and diffusion length on the electron-beam-induced current and its derivative Determination of diffusion lengths in the low micron and submicron ranges

A systematic and quantitative analysis is carried out to investigate the effects of the shape (point, cube, Gaussian) and size of the generation volume, the surface recombination velocity, and the diffusion length on the electron-beam-induced current (EBIC) and its derivative (DEIC). Thick homogeneously doped samples exhibiting diffusion lengths in the low micron and submicron range are considered. The results are presented in computed EBIC curves as a function of scanning distance and of the ratio true diffusion length/effective diffusion length. Shown using these curves are: (1) a simple and yet rigorous method for the determination of the true diffusion length, taking into consideration all of the factors cited above, (2) a method for the rapid determination of the surface recombination velocity, (3) the condition under which the source shape becomes insignificant, and (4) a new value for the lower limit of the diffusion length which can be determined by the EBOC technique.

Luke, K. L.↗
DOE OSTI2022

Reduced Surface Recombination Velocity in Mixed-Cation Mixed-Halide Hybrid Perovskite Devices Leads to Improved Open-Circuit Voltage

Surface recombination plays an important role in perovskite solar cell performance.Despite rapid progress, the record power conversion efficiency (PCE, ~ 25.7%) for perovskite single-junction solar cells still lags behind its theoretical limit (~ 32%), largely due to the open circuit voltage (VOC) deficit that results from non-radiative recombination at the bulk of perovskite films and the interfaces between perovskite and transport layers. In this work, we show that (3-aminopropyl)trimethoxysilane (APTMS) surface passivation can reduce the surface recombination velocities (SRVs) of perovskite solar cells, thus improving device VOC and PCE.

perovskite solar cell, surface recombination, surf↗
NASA NTRS1993

Measurement of the minority carrier diffusion length and edge surface-recombination velocity in InP

A scanning electron microscope (SEM) was used to measure the electron (minority carrier) diffusion length (L(sub n)) and the edge surface-recombination velocity (V(sub s)) in zinc-doped Czochralski-grown InP wafers. Electron-beam-induced current (EBIC) profiles were obtained in specimens containing a Schottky barrier perpendicular to the scanned (edge) surface. An independent technique was used to measure V(sub s), and these values were used in a theoretical expression for normalized EBIC. A fit of the experimental data with this expression enabled us to determine L(sub n).

Bailey, Sheila G.↗
NASA NTRS1993

Minority carrier diffusion length and edge surface-recombination velocity in InP

A scanning electron microscope was used to obtain the electron-beam-induced current (EBIC) profiles in InP specimens containing a Schottky barrier perpendicular to the scanned (edge) surface. An independent technique was used to measure the edge surface-recombination velocity. These values were used in a fit of the experimental EBIC data with a theoretical expression for normalized EBIC (Donolato, 1982) to obtain the electron (minority carrier) diffusion length.

Hakimzadeh, Roshanak↗
NASA NTRS1987

Analysis of the interaction of a laser pulse with a silicon wafer - Determination of bulk lifetime and surface recombination velocity

The decay of excess minority carriers produced in a silicon wafer of thickness d by a laser pulse is analyzed. A comprehensive theory based on this analysis is presented for the determination of bulk lifetime Tau(b) and surface recombination velocity S. It is shown that, starting with an exponential spatial profile, the carrier profile assumes a spatially symmetrical form after approximately one time constant of the fundamental mode of decay. Expressions for the spatial average of the carrier density as a function of time are derived for three temporal laser pulse shapes: impulse, square, and Gaussian. Particular attention is paid to the time constants of the fundamental and higher modes of decay. The ratios of the time constants of the higher modes to the fundamental mode, as well as the time constant of the fundamental mode, are presented over wide ranges of values of S and d. For Sd less than about 40 sq cm/s, a two-wafer method is developed to determine Tau(b) and S; it is also shown that the requirement of d/Tau(b) greater than about 20S is sufficient to adequately guarantee that the asymptotic value of the instantaneous observed lifetime differs from the bulk lifetime by no more than 10 percent.

Luke, Keung L.↗