Hole-blocking crystalline-silicon/titanium-oxide heterojunction with very low interface recombination velocity

Jhaveri, Janam; Avasthi, Sushobhan; Man, Gabriel; McClain, W. E.; Nagamatsu, Ken A.; Kahn, Antoine; Schwartz, Jeffrey; Sturm, James C.

doi:10.1109/pvsc.2013.6745154

Cited by 29 publications

(18 citation statements)

References 9 publications

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“…The experimental setup used in this investigation does not contain tools to measure the energy of the conduction band minimum (CBM); hence, a direct determination of the TiO 2 band gap is not possible. Nevertheless, similar investigations performed by Jhaveri et al, 17 in which ultrathin TiO 2 films of 1−4 nm are deposited on Si substrates, have found the VBM of TiO 2 located at 3.8 eV below E F and measured a band gap of 4.6 eV. DFT investigations also found that the band gap of anatase-TiO 2 containing oxygen vacancies is 3.9 and 4.4 eV at the Γ and X points, respectively.…”

Section: Xuv Photoemission Spectroscopysupporting

confidence: 62%

Femtosecond Extreme Ultraviolet Photoemission Spectroscopy: Observation of Ultrafast Charge Transfer at the n-TiO₂/p-Si(100) Interface with Controlled TiO₂ Oxygen Vacancies

Vaida¹,

Leone

2016

J. Phys. Chem. C

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Wide band gap heterostructures can be accurately fabricated at room temperature to exhibit remarkable electrical properties that facilitate the transfer of electrons across the heterojunction while blocking the transfer of holes. The present investigation focuses on engineering the electronic structure of a TiO 2 overlayer on a p-type doped Si(100) substrate by controlling the concentration of TiO 2 oxygen vacancies. TiO 2 films are deposited on p-Si(100) in an ultrahigh vacuum setup by evaporation of Ti atoms at a constant rate in a variable O 2 atmosphere. The concentration of oxygen vacancies and consequently the degree of n-type doping of TiO 2 is tuned by controlling the oxygen background pressure during the TiO 2 formation. To investigate the electronic structure and the concentration of defects in the TiO 2 layer as well as to characterize the TiO 2 /p-Si(100) band alignment we used photoelectron spectroscopy employing femtosecond extreme ultraviolet laser pulses produced via high harmonic generation. Furthermore, using a pump−probe technique in conjunction with photoemission spectroscopy, an ultrafast electron injection from the p-Si(100) substrate into the defect-rich TiO 2 layer is observed with a time constant of 450 fs, as well as the subsequent charge carrier recombination. The latter is revealed to be affected by the oxygen defects when investigated with femtosecond resolution. No charge transfer is observed when defect-poor TiO 2 films are prepared on the p-Si(100) substrate. This might be attributed to a change in the energy band alignment at the TiO 2 /Si(100) interface that reduces the built-in potential across the heterojunction and consequently reduces the driving force responsible for the injection of electrons into the TiO 2 layer.

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Section: Xuv Photoemission Spectroscopysupporting

confidence: 62%

Femtosecond Extreme Ultraviolet Photoemission Spectroscopy: Observation of Ultrafast Charge Transfer at the n-TiO₂/p-Si(100) Interface with Controlled TiO₂ Oxygen Vacancies

Vaida¹,

Leone

2016

J. Phys. Chem. C

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“…This results in an interface recombination velocity for holes of approximately

S = 1 \times 10^{5} normalcm s^{- 1}

. Compared with other reports on heterojunction solar cells and heterostructures, this value is rather large . The NiO/ZnO interface thus seems to strongly impede carrier collection.…”

Section: Resultsmentioning

confidence: 75%

Semi‐transparent NiO/ZnO UV photovoltaic cells

Karsthof

Räcke

Wenckstern

et al. 2015

Physica Status Solidi (a)

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Semi‐transparent pn‐heterojunctions were fabricated from pulsed laser deposited (PLD) n‐type ZnO and DC magnetron sputtered p‐type NiO, working as UV‐active solar cells. The complete cell stack has an average transmission of 46% in the visible spectral range and an optical absorption edge at 380 nm. The diodes exhibit high current rectification of up to eight orders of magnitude at ±2 V. Upon illumination with a solar simulator, the devices show photovoltaic activity with open‐circuit voltages of up to 520 mV, short‐circuit current densities of 0.5 mAcm2, and a maximum external quantum efficiency of 55%. However, we observed rather low fill factors of the current–voltage characteristics of around 40%, resulting in total power conversion efficiencies of around 0.1% and efficiencies in the UV range of 3.1%. To identify possible loss mechanisms, the voltage‐dependent efficiency of carrier collection was calculated. The data were fitted using a model that considers recombination losses at the NiO/ZnO interface as well as within the electric field region, yielding a high hole interface recombination velocity of 1×105cm s−1. We conclude that the carrier collection efficiency is strongly deteriorated by recombination losses at the NiO/ZnO interface, causing a strong bending of the jV characteristics under illumination and thereby low fill factors.

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“…The small fluctuation in the range of 500-1000 nm could be due to measurement error. It is well known that the passivation effect of TiO 2 would be degraded by annealing over 350°C, which affects the decrease in carrier lifetime and open circuit voltage [16,17]. Therefore, another passivation layer like a silicon dioxide should be inserted between silicon and TiO 2 to achieve higher open circuit voltage, which is a future subject of study in our group.…”

Section: Solar Cells With Al 2 O 3 /Tio 2 Arc Filmmentioning

confidence: 96%

Al₂O₃/TiO₂ double layer anti‐reflection coating film for crystalline silicon solar cells formed by spray pyrolysis

Kanda

Üzüm

Harano

et al. 2016

Energy Science & Engineering

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An Al 2 O 3 /TiO 2 double layer anti-reflection coating (ARC) film formed by spray pyrolysis was introduced for monocrystalline silicon solar cells as the nonvacuum processing method. The thickness of the Al 2 O 3 layer and TiO 2 compact layer was controlled by the volume of deposited precursor solution and confirmed by ellipsometry and scanning electron microscopy. The average photovoltaic properties of photocurrent density (J sc ), open-circuit photovoltage (V oc ), fill factor (FF), and photo energy conversion efficiency (η) were 37.0 mA/cm 2 , 590 mV, 0.712, and 15.5%, respectively. A significant improvement on J sc and η could be confirmed owing to the Al 2 O 3 /TiO 2 ARC. The results of Fourier transform infrared (FTIR) spectroscopy and optical simulation with modeling for the reflectance properties confirmed that C-H-based organics remained after the deposition of thin films.

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Hole-blocking crystalline-silicon/titanium-oxide heterojunction with very low interface recombination velocity

Cited by 29 publications

References 9 publications

Femtosecond Extreme Ultraviolet Photoemission Spectroscopy: Observation of Ultrafast Charge Transfer at the n-TiO₂/p-Si(100) Interface with Controlled TiO₂ Oxygen Vacancies

Femtosecond Extreme Ultraviolet Photoemission Spectroscopy: Observation of Ultrafast Charge Transfer at the n-TiO₂/p-Si(100) Interface with Controlled TiO₂ Oxygen Vacancies

Semi‐transparent NiO/ZnO UV photovoltaic cells

Al₂O₃/TiO₂ double layer anti‐reflection coating film for crystalline silicon solar cells formed by spray pyrolysis

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Hole-blocking crystalline-silicon/titanium-oxide heterojunction with very low interface recombination velocity

Cited by 29 publications

References 9 publications

Femtosecond Extreme Ultraviolet Photoemission Spectroscopy: Observation of Ultrafast Charge Transfer at the n-TiO2/p-Si(100) Interface with Controlled TiO2 Oxygen Vacancies

Femtosecond Extreme Ultraviolet Photoemission Spectroscopy: Observation of Ultrafast Charge Transfer at the n-TiO2/p-Si(100) Interface with Controlled TiO2 Oxygen Vacancies

Semi‐transparent NiO/ZnO UV photovoltaic cells

Al2O3/TiO2 double layer anti‐reflection coating film for crystalline silicon solar cells formed by spray pyrolysis

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Product

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Femtosecond Extreme Ultraviolet Photoemission Spectroscopy: Observation of Ultrafast Charge Transfer at the n-TiO₂/p-Si(100) Interface with Controlled TiO₂ Oxygen Vacancies

Femtosecond Extreme Ultraviolet Photoemission Spectroscopy: Observation of Ultrafast Charge Transfer at the n-TiO₂/p-Si(100) Interface with Controlled TiO₂ Oxygen Vacancies

Al₂O₃/TiO₂ double layer anti‐reflection coating film for crystalline silicon solar cells formed by spray pyrolysis