Diffractive Backside Structures via Nanoimprint Lithography

AbstractFor decreasing thicknesses of wafer based silicon solar cells, photon management structures to maintain high quantum efficiencies will gain importance. Diffractive gratings on the wafer back side can be designed to achieve very high path length enhancements, especially for weakly absorbed infrared radiation. This technologically demanding concept has to be realised using processes with upscaling potential. Therefore, we present a fabrication process for producing photonic structures in silicon based on interference lithography and nanoimprint lithography (NIL).We realised linear as well as crossed gratings of different depths, which were etched into the wafer back side. Polarisation dependent reflection measurements were made to get information about potential absorption enhancement as well as the occurrence of parasitic absorption in the metal reflector. This is conducted for a PECVD silicon oxide buffer layer between grating and reflector as well as a spin coated silicon oxide layer. Besides these optical characterisations, we further investigated the electrical properties of the back surface, where we applied a concept in which electrical and optical properties are decoupled. This is realised by a layer stack on the wafer back side, consisting of a thin Al2O3 passivation and a doped amorphous silicon layer

Silicon solar cell–integrated stress and temperature sensors for photovoltaic modules

We propose silicon solar cell–integrated stress and temperature sensors as a new approach for the stress and temperature measurement in photovoltaic (PV) modules. The solar cell–integrated sensors enable a direct and continuous in situ measurement of mechanical stress and temperature of solar cells within PV modules. In this work, we present a proof of concept for stress and temperature sensors on a silicon solar cell wafer. Both sensors were tested in a conventional PV module setup. For the stress sensor, a sensitivity of (−47.41 ± 0.14)%/GPa has been reached, and for the temperature sensor, a sensitivity of (3.557 ± 0.008) × 10$^{-3}$ K$^{-1}$ has been reached. These sensors can already be used in research for increased measurement accuracy of the temperature and the mechanical stress in PV modules because of the implementation at the precise location of the solar cells within a laminate stack, for process evaluation, in‐situ measurements in reliability tests, and the correlation with real exposure to climates

Using waste to reduce slope erosion on road embankments

“Permission is granted by ICE Publishing to print one copy for personal use. Any other use of these PDF files is subject to reprint fees" (www.transport-ice.com). http://dx.doi.org/10.1680/tran.2006.159.1.15Urban waste may be used to reduce slope erosion of highway embankments. Whereas different kinds of compost have been tested in the USA for highway revegetation, sewage sludge has been used only for agricultural purposes. This paper presents the results of research carried out in order to study the viability of the application of sewage sludge compared with compost. Test areas measuring 4 m 3 5 m were constructed on a new highway embankment with 2 : 1 and 3 : 2 side slopes in the south of Spain. Crop cover and erosion were evaluated for plots with application of three dosages of compost and three dosages of sludge. Also, the costs of the proposed application are analysed. This treatment costs, on average, 0.24% of the budget for new roads infrastructure, and reduces soil loss by up to 30% on average. Based on these results, compost and sludge can be successfully used to reduce slope erosion on highway embankments. However, standards and specifications are required for their routine application.Department of Civil Engineering, University of Granada, Spai

Micro-spectroscopy on silicon wafers and solar cells

Micro-Raman (μRS) and micro-photoluminescence spectroscopy (μPLS) are demonstrated as valuable characterization techniques for fundamental research on silicon as well as for technological issues in the photovoltaic production. We measure the quantitative carrier recombination lifetime and the doping density with submicron resolution by μPLS and μRS. μPLS utilizes the carrier diffusion from a point excitation source and μRS the hole density-dependent Fano resonances of the first order Raman peak. This is demonstrated on micro defects in multicrystalline silicon. In comparison with the stress measurement by μRS, these measurements reveal the influence of stress on the recombination activity of metal precipitates. This can be attributed to the strong stress dependence of the carrier mobility (piezoresistance) of silicon. With the aim of evaluating technological process steps, Fano resonances in μRS measurements are analyzed for the determination of the doping density and the carrier lifetime in selective emitters, laser fired doping structures, and back surface fields, while μPLS can show the micron-sized damage induced by the respective processes

Verfahren zur lokalen Hochdotierung und Kontaktierung einer Halbleiterstruktur, welche eine Solarzelle oder eine Vorstufe einer Solarzelle ist

Die Erfindung betrifft ein Verfahren zur lokalen Hochdotierung und Kontaktierung einer Halbleiterstruktur, welche eine Solarzelle oder eine Vorstufe einer Solarzelle ist und ein Silizium-Halbleitersubstrat (1) eines Basisdotierungstyps umfasst, wobei die Hochdotierung und Kontaktierung erfolgt durch Erzeugen mehrerer lokaler Hochdotierungsbereiche des Basisdotierungstyps in dem Halbleitersubstrat (1) an einer Kontaktierungsseite (1a) des Halbleitersubstrates und Aufbringen einer metallischen Kontaktierungsschicht (7) auf die Kontaktierungsseite (1a) oder gegebenenfalls eine oder mehrere die Kontaktierungsseite (1a) ganz oder teilweise bedeckende Zwischenschichten, zur Ausbildung elektrisch leitender Verbindungen zwischen der metallischen Kontaktierungsschicht (7) und dem Halbleitersubstrat (1) an den Hochdotierungsbereichen.; Wesentlich ist, dass das Verfahren folgende Verfahrensschritte umfasst: A Erzeugen einer die Kontaktierungsseite (1a) des Halbleitersubstrates bedeckende Schichtstruktur, umfassend - eine Dotierschicht (3), welche einen Dotierstoff des Basisdotierungstyps enthält und ausgebildet wird als Schicht aus amorphem Silizium oder als Schicht aus amorphem Siliziumcarbid mit einem Kohlenstoffgehalt kleiner 10at% und - eine Reflexionsschicht (4), welche zumindest in dem Wellenlängenbereich zwischen 800 nm und 1200 nm mit einem Brechungsindex nR kleiner dem Brechungsindex nHS des Halbleitersubstrates ausgebildet wird, wobei die Dotierschicht (3) in der Schichtabfolge näher an der Kontaktierungsseite (1a) liegend als die Reflexionsschicht (4) ausgebildet wird,; B lokales Erhitzen der Schichtstruktur und der darunter liegenden Oberfläche des Halbleitersubstrates an mehreren Zonen zur Ausbildung von lokalen Hochdotierungsbereichen, wobei die lokale Erhitzung derart erfolgt, dass sich an den lokal erhitzten Bereichen jeweils lokal eine Schmelzmischung aus zumindest der Dotierschicht (3) und einem Teilbereich des Halbleitersubstrates an der Kontaktierungsseite (1a) ausbildet und sich bei Erstarren der Schmelzmischung ein durch zumindest den Dotierstoff der Dotierschicht (3) stärker dotierter Hochdotierungsbereich (6) in dem Halbleitersubstrat (1) an der Kontaktierungsseite (1a) ausbildet und C Aufbringen einer metallischen Kontaktierungsschicht (7), zur Ausbildung einer elektrisch leitenden Verbindung zwischen Halbleitersubstrat (1) und Kontaktierungsschicht (7) an den Hochdotierungsbereichen

Excellent silicon surface passivation with 5 Å thin ALD Al2O3 layers: Influence of different thermal post-deposition treatments

Thin layers of Al2O3 always require a thermal post-deposition treatment to activate the passivation on crystalline silicon surfaces. In this work, we studied the influence of different thermal post-deposition treatments for the activation of passivating ALD Al2O3 single layers and Al2O3/SiNx stacks. For the stacks, especially with less than 5 nm Al2O3, a short high temperature process at 800 °C results in a remarkably lower surface recombination compared to a commonly applied annealing at 425 °C. We observed that four ALD cycles of Al2O3 are sufficient to reach the full potential of surface passivation, and even with one atomic layer of Al2O3 (one ALD cycle) emitter saturation current densities as low as 45 fA/cm2 can be reached on boron-diffused emitters

Submicron resolution carrier lifetime analysis in silicon with Fano resonances

Defect rich regions in multicrystalline silicon are by Raman spectroscopy at high and low injection levels. analyzing the Fano type asymmetny and the spectral of the first order Raman peak crucial properties such as combination lifetime, doping density and -stress can be tracted simultaneously. Due to the small wavelength of the excitation laser thhe spatial resolution of these measurements is significantly below 1 mu m which gives new insight into thhe impact of defects on the carrier recombination lifetime. The results are evaluated by comparing them to micro-photoluminescence and synchrotron X-ray fluorescence measurements

Influence of metal-organic vapor phase epitaxy reactor environment on the silicon bulk lifetime

III-V multijunction solar cells grown on a Si solar cell are an attractive approach to reduce the cost of high-efficiency solar cells. When using the Si wafer as an active solar cell, it is crucial to avoid degradation of the minority carrier lifetime in the Si during the metal-organic vapor phase epitaxy (MOVPE) process. After heating a Si wafer in a MOVPE reactor under a H2 atmosphere, we observed a strong degradation of its lifetime. By analyzing the annealed samples with photoluminescence and quasi-steady-state photoconductance, we found an iron contamination of up to 2 × 1012 cm-3. The measured iron concentration could be identified as the major source for the decrease of the minority carrier lifetimes of the Si wafers. By using diffusion barriers, we identified the graphite susceptor as the main source of the iron contamination. This knowledge offers pathways to preserve the minority carrier lifetime in the Si wafers during the MOVPE process