N-type Black Silicon Solar Cells

Black silicon is an interesting surface texture for solar cells because of its extremely low reflectance on a wide wavelength range and acceptance angle. In this paper we present how black silicon (b-Si) texturization can be applied on the boron doped front surface of an n-type solar cell resulting in an efficiency of 18.7%. We show that the highly boron doped emitter can be formed on black silicon without losing its good optical properties and that atomic layer deposited aluminum oxide provides good surface passivation on these boron doped b-Si emitters.Peer reviewe

Passivation of black silicon boron emitters with atomic layer deposited aluminum oxide

The nanostructured surface – also called black silicon (b-Si) – is a promising texture for solar cells because of its extremely low reflectance combined with low surface recombination obtained with atomic layer deposited (ALD) thin films. However, the challenges in keeping the excellent optical properties and passivation in further processing have not been addressed before. Here we study especially the applicability of the ALD passivation on highly boron doped emitters that is present in crystalline silicon solar cells. The results show that the nanostructured boron emitters can be passivated efficiently using ALD Al2O3 reaching emitter saturation current densities as low as 51 fA/cm2. Furthermore, reflectance values less than 0.5% after processing show that the different process steps are not detrimental for the low reflectance of b-Si.Peer reviewe

Full-Wafer Roller-NIL Processes for Silicon Solar Cell Texturisation

The highest solar cell efficiencies both for c-Si and mc-Si were reached using template based texturing processes. Especially for mc-Si the benefit of a defined texture, the so called honeycomb texture, was demonstrated impressively. However, up until now, no industrially feasible process has been available to pattern the necessary etching masks with the sufficient resolution. Roller-Nanoimprint Lithography (Roller-NIL) has the potential to overcome these limitations and to allow high quality pattern transfers, even in the sub-micron regime, in continuous in-line processes. Therefore, this etch-mask patterning technique is a suitable solution to bring such elaborate features like the honeycomb texture to an industrial realization. Beyond that, this fast printing-like technology opens up new possibilities to introduce promising concepts like photonic structures into solar cells

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

Nanoimprinted diffraction gratings for crystalline silicon solar cells: implementation, characterization and simulation

Light trapping is becoming of increasing importance in crystalline silicon solar cells as thinner wafers are used to reduce costs. In this work, we report on light trapping by rear-side diffraction gratings produced by nano-imprint lithography using interference lithography as the mastering technology. Gratings fabricated on crystalline silicon wafers are shown to provide significant absorption enhancements. Through a combination of optical measurement and simulation, it is shown that the crossed grating provides better absorption enhancement than the linear grating, and that the parasitic reflector absorption is reduced by planarizing the rear reflector, leading to an increase in the useful absorption in the silicon. Finally, electro-optical simulations are performed of solar cells employing the fabricated grating structures to estimate efficiency enhancement potential

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

Improved Silicon Surface Passivation by ALD Al2O3/SiO2 Multilayers with In‐Situ Plasma Treatments

Abstract Al2O3 is one of the most effective dielectric surface passivation layers for silicon solar cells, but recent studies indicate that there is still room for improvement. Instead of a single layer, multilayers of only a few nanometers thickness offer the possibility to tailor material properties on a nanometer scale. In this study, the effect of various plasma treatments performed at different stages during the ALD deposition of Al2O3/SiO2 multilayers on the silicon surface passivation quality is evaluated. Significant improvements in surface passivation quality for some plasma treatments are observed, particularly for single Al2O3/SiO2 bilayers treated with a H2 plasma after SiO2 deposition. This treatment resulted in a surface recombination parameter J0 as low as 0.35 fA cm−2 on (100) surfaces of 10 Ω cm n‐type silicon, more than a factor of 5 lower than that of Al2O3 single layers without plasma treatment. Capacitance‐voltage measurements indicate that the improved surface passivation of the plasma‐treated samples results from an enhanced chemical interface passivation rather than an improved field effect. In addition, a superior temperature stability of the surface passivation quality is found for various plasma‐treated multilayers

Photovoltaische Solarzelle und Verfahren zum Herstellen einer photovoltaischen Solarzelle

Die Erfindung betrifft eine photovoltaische Solarzelle, umfassend ein Siliziumsubstrat mit einer auf einer Rückseite des Siliziumsubstrates mittelbar oder unmittelbar angeordneten Tunnelschicht und einer auf der Tunnelschicht mittelbar oder unmittelbar angeordneten Siliziumschicht, welche Siliziumschicht eine Mehrzahl alternierend angeordneter p- und n-dotierter Bereiche aufweist. Die Erfindung ist dadurch gekennzeichnet, dass in der Siliziumschicht zwischen den p-dotierten und n-dotierten Bereichen jeweils ein undotierter Bereich angeordnet ist