Papers by Bernd Stannowski
AIP Conference Proceedings
Integrating transparent conductive oxides to improve the infrared response of silicon solar cells... more Integrating transparent conductive oxides to improve the infrared response of silicon solar cells with passivating rear contacts
Journal of Materials Chemistry A, 2014
ABSTRACT The use of relatively low purity zinc nitrate for electrochemical deposition of compact ... more ABSTRACT The use of relatively low purity zinc nitrate for electrochemical deposition of compact ZnO films is attractive for large scale production because of the cost saving potential. ZnO films were grown on SnO2:F and magnetron sputtered ZnO:Al templates using a three electrode potentiostatic system in galvanic mode. The electrolyte consisted of a 0.1 M zinc nitrate solution (either 99.998% or 99% purity) and 1 mM aluminium nitrate for extrinsic doping, when required. Moderate deposition rates of up to 0.9 nm s−1 were achieved on ZnO:Al templates with lower rates of up to 0.5 nm s−1 on SnO2:F templates. Observation of SEM images of the films revealed a wall-like morphology whose lateral thickness (parallel to the substrate) reduced as aluminium was added to the system either in the electrolyte or from the substrate. However, pre-deposition activation of the template by applying a negative voltage (approximately −2 V) allowed the growth of compact films even for the low purity electrolyte. The optical band gap energy of intrinsically doped films was lower than that of the Al doped films. The composite electrical conductivity of all the films studied, as inferred from sheet resistance and Hall effect measurements of the ZnO/template stacks was much less than that of the uncoated templates. A strong E2 (high) mode at around 437 cm−1 was visible in the Raman spectra for most films confirming the formation of ZnO. However, both the Raman modes and XRD reflections associated with wurtzite ZnO diminished for the Al doped films indicating a high level of mainly oxygen related defects. Based on these data, further studies are underway to improve the doping efficiency of aluminium, the crystalline structure and thus the conductivity of such films.
MRS Proceedings, 2000
Direct deposition of polycrystalline silicon (poly-Si) thin films by the Hot Wire CVD method has ... more Direct deposition of polycrystalline silicon (poly-Si) thin films by the Hot Wire CVD method has been used for the first time for the fabrication of poly-Si top gate Thin Film Transistors (TFTs). The TFTs have a high electron mobility in saturation of up to 4 cm 2 V -1 s -1 as well as a remarkably large ON/OFF ratio of up to 6 x 10 5 .
MRS Proceedings, 1999
We present state-of-the-art thin-film transistors (TFTs) incorporating amorphous silicon ilayers ... more We present state-of-the-art thin-film transistors (TFTs) incorporating amorphous silicon ilayers deposited by hot-wire chemical vapor deposition. The TFTs are deposited on glowdischarge silicon nitride as well as on thermally-grown silicon dioxide. The devices on silicon nitride have a field-effect mobility above 0.7 cm 2 /Vs, a threshold voltage around 2 V and a subthreshold slope as low as 0.5 V/dec. As commonly observed, the TFTs on silicon-dioxide have higher values for the threshold voltage and the sub-threshold slope. In the annealed state the hotwire TFTs show almost the same properties as TFTs deposited by conventional plasma-enhanced chemical vapor deposition. Nevertheless, the stress-time dependent behavior under prolonged gate-voltage stress at elevated temperature is different from that of the glow-discharge devices. The hot-wire TFTs are clearly more stable than their glow-discharge counterparts. Furthermore, we found differences in the stress behavior of the hot-wire TFTs deposited on silicon nitride and silicon dioxide.
MRS Proceedings, 2001
ABSTRACT
Applied Physics Letters, 2015
ABSTRACT We have developed a microcrystalline silicon oxide (μc-SiOx:H) p-type emitter layer that... more ABSTRACT We have developed a microcrystalline silicon oxide (μc-SiOx:H) p-type emitter layer that significantly improves the light incoupling at the front side of silicon heterojunction solar cells by minimizing reflection losses. The μc-SiOx:H p-layer with a refractive index of 2.87 at 632 nm wavelength and the transparent conducting oxide form a stack with refractive indexes which consecutively decrease from silicon to the ambient air and thus significantly reduce the reflection. Optical simulations performed for flat wafers reveal that the antireflective effect of the emitter overcompensates the parasitic absorption and suggest an ideal thickness of about 40 nm. On textured wafers, the increase in current density is still more than 1 mA/cm2 for a typical emitter thickness of 10 nm. Thus, we are able to fabricate heterojunction solar cells with current densities significantly over 40 mA/cm2 and power conversion efficiency above 20%, which is yet mainly limited by the cell's fill factor.
Energy Procedia, 2014
Optical and electrical properties of p-type doped hydrogenated amorphous silicon (p-a-Si:H), used... more Optical and electrical properties of p-type doped hydrogenated amorphous silicon (p-a-Si:H), used as window emitter layer in silicon based hetero junction (a-Si:H/c-Si HJ) solar cells, are investigated. These properties were investigated by comparing diborane (B 2 H 6 ) and trimethylboron (B(CH 3 ) 3 , TMB) as doping gas analyzing the deposition temperature dependence. A wider optical band gap (E 04 >1.9 eV) and lower refractive index (n) is observed for TMB-doped layers, which we ascribe to carbon incorporation. a-Si:H/c-Si HJ solar cells with p-doped emitter layers using TMB and B 2 H 6 were fabricated. For cells with TMBdoped layers an increased photocurrent of up to 1.5 mA/cm 2 is found, which is due to a reduction in parasitic absorption. However, cells with TMB-doped emitter also show a higher series resistance, which we attribute to increased electrical losses at the TCO/p-contact.
International Journal of Photoenergy, 2015
Microcrystalline silicon ( c-Si:H) thin-film solar cells are processed on glass superstrates havi... more Microcrystalline silicon ( c-Si:H) thin-film solar cells are processed on glass superstrates having both micro-and nanoscale surface textures. The microscale texture is realised at the glass surface, using the aluminium-induced texturing (AIT) method, which is an industrially feasible process enabling a wide range of surface feature sizes (i.e., 700 nm-3 m) of the textured glass. The nanoscale texture is made by conventional acid etching of the sputter-deposited transparent conductive oxide (TCO). The influence of the resulting "double texture" on the optical scattering is investigated by means of atomic force microscopy (AFM) (studying the surface topology), haze measurements (studying scattering into air), and short-circuit current enhancement measurements (studying scattering into silicon). A predicted enhanced optical scattering efficiency is experimentally proven by a short-circuit current enhancement Δ sc of up to 1.6 mA/cm 2 (7.7% relative increase) compared to solar cells fabricated on a standard superstrate, that is, planar glass covered with nanotextured TCO. Enhancing the autocorrelation length (or feature size) of the AIT superstrates might have the large potential to improve the c-Si:H thin-film solar cell efficiency, by reducing the shunting probability of the device while maintaining a high optical scattering performance.
EPJ Photovoltaics, 2014
A key process in thin film silicon-based solar cell manufacturing is plasma enhanced chemical vap... more A key process in thin film silicon-based solar cell manufacturing is plasma enhanced chemical vapor deposition (PECVD) of the active layers. The deposition process can be monitored in situ by plasma diagnostics. Three types of complementary diagnostics, namely optical emission spectroscopy, mass spectrometry and non-linear extended electron dynamics are applied to an industrial-type PECVD reactor. We investigated the influence of substrate and chamber wall temperature and chamber history on the PECVD process. The impact of chamber wall conditioning on the solar cell performance is demonstrated.
Photonics for Solar Energy Systems V, 2014
ABSTRACT We present a-Si:H/µc-Si:H tandem solar cells on laser textured ZnO:Al front contact laye... more ABSTRACT We present a-Si:H/µc-Si:H tandem solar cells on laser textured ZnO:Al front contact layers. Direct pulsed laser interference patterning (DLIP) was used for writing arrays of one-dimensional micro gratings of submicron period into ZnO:Al films. The laser texture provides good light trapping which is indicated by an increase in short-circuit current density of 20% of the bottom cell limited device compared to cells on planar ZnO:Al. The open-circuit voltage of the cells on laser textured ZnO:Al is almost the same as for cells on planar substrates, indicating excellent growth conditions for amorphous and microcrystalline silicon on the U-shaped grating grooves. DLIP is a simple, single step and industrially applicable method for large area periodic texturing of ZnO:Al thin films. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)
Hydrogen generated by conversion of sunlight into chemical energy is considered as a fuel of the ... more Hydrogen generated by conversion of sunlight into chemical energy is considered as a fuel of the future replacing fossil carbon and hydrocarbons. A sustainable and environmentally acceptable way to produce H 2 is by the photoelectrolysis of water, i.e. the conversion of solar into chemical energy by water splitting. For this purpose we modified a triple junction amorphous / microcrystalline silicon (3j a-Si/µc-Si) thin film solar cell in superstrate configuration. In a first approach Pt and RuO 2 nanoparticles were used as catalysts. The solar to fuel efficiency (SFE) of this PV hybrid electrolyser was ≤ 3.7%. We then replaced the platinum by MoS 2 as an alternative low-cost hydrogen evolving catalyst. For this purpose crystalline MoS 2 nano-sheets were deposited enveloping multi-walled carbon nanotubes. Compared to other preparation strategies, MWNCT-supported MoS 2 has the advantage of a higher corrosion stability in the hydrogen evolution reaction. Deposited as a blend with PEDOT:PSS on the backside of the solar cell a SFE of 2.5% was yielded.
Plasma Processes and Polymers, 2014
ABSTRACT The advanced opto-electronic properties of microcrystalline silicon oxide (µc-SiOx:H) th... more ABSTRACT The advanced opto-electronic properties of microcrystalline silicon oxide (µc-SiOx:H) thin film layers deposited by means of plasma enhanced chemical vapor deposition (PECVD) resulted in several applications of this material especially in solar cells and modules in the last years. We investigated the plasma chemistry during the PECVD of µc-SiOx:H using in situ plasma diagnostics. Plasma properties are related to the properties of resulting µc-SiOx:H films measured ex situ. Two different deposition regimes were identified. Besides the standard low pressure regime, a high pressure regime was found, which lead to µc-SiOx:H layers with high crystallinities and low refractive indices.
Nanotechnology, Jan 14, 2014
We present an experimental study on the influence of annealing temperature on morphological chang... more We present an experimental study on the influence of annealing temperature on morphological changes of colloidal silver nanoparticles (Ag NPs) and their optical response. Monodisperse colloidal Ag NPs with diameter of 164 nm ± 15 nm have been fabricated by a facile two-step synthesis approach. The annealing effects on the Ag NPs have been investigated by means of optical measurements, scanning electron microscopy, x-ray photoelectron spectroscopy and x-ray diffraction. By annealing up to 440 °C morphology and chemical compositions of the Ag NPs changed. These changes affect the particle size and distribution, surface morphology, crystallinity and, most importantly, the oxidation state of the surface layer. The removal of an oxide layer leads to stronger light scattering from the nanoparticles and decreases parasitic light absorption at wavelengths above 400 nm. Strong light trapping has been observed for a silicon thin film with embedded annealed Ag NPs. This study demonstrates that...
IEEE Journal of Photovoltaics, 2014
ABSTRACT Liquid-phase crystallized silicon absorber layers have been applied in heterojunction so... more ABSTRACT Liquid-phase crystallized silicon absorber layers have been applied in heterojunction solar cells on glass substrates with 10.8 % conversion efficiency and an open-circuit voltage of 600 mV. Intermediate layers of SiOx, SiNx, and SiOxNy, as well as the a-Si:H precursor layer, were deposited on 30 cm × 30 cm glass substrates using industrial-type plasma-enhanced chemical vapor deposition equipment. After crystallization on 3 cm × 5 cm area using a continuous-wave infrared laser line, the resulting polysilicon material showed high material quality with large grain sizes.
2011 37th IEEE Photovoltaic Specialists Conference, 2011
ABSTRACT In this contribution we compare the optical, electronic and surface morphological proper... more ABSTRACT In this contribution we compare the optical, electronic and surface morphological properties of various textured transparent conducting oxides (TCO) based on zinc oxide and fluorine doped tin oxide. Since the TCO material properties tend to be interrelated, comparison of such films is a rather complex exercise. The TCO films were characterised by atomic force microscopy, scanning electron microscopy, spectrophotometry, angle resolved scattering, four point probe and Hall Effect measurements. Thereafter, an attempt was made to correlate the TCO material properties with the corresponding current-voltage characteristics and quantum efficiency in actual solar cells. It was found that the solar cells were more sensitive to changes in the optical properties of the TCO substrates than to those in the sheet resistance. Based on these results, we recommend that when optimising TCO films for thin film silicon production, the first priority should be to obtain the highest transmittance possible and then to tune the electrical properties accordingly.
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Papers by Bernd Stannowski