The fast determination of the spatially resolved series resistance of silicon solar cells from luminescence images is demonstrated. Strong lateral variation of the series resistance determined from luminescence images taken on an industrial screen printed silicon solar cell is confirmed qualitatively by a Corescan measurement and quantitatively by comparison with the total series resistance obtained from the terminal characteristics of the cell. Compared to existing techniques that measure the spatially resolved series resistance, luminescence imaging has the advantage that it is nondestructive and orders of magnitude faster. © 2007 American Institute of Physics. DOI: 10.1063/1.2709630 The series resistance of silicon solar cells often exhibits strong lateral variations, particularly in industrial screen printed cells. Experimental techniques to quantify such variations include Corescan, 1 Cello, 2 and imaging techniques based on dark and illuminated infrared lock-in thermography LIT. 3,4 These techniques require data acquisition times between minutes and several hours per solar cell. Electroluminescence EL and photoluminescence PL imaging are very fast characterization tools for silicon solar cells and silicon wafers, with data acquisition times of a few seconds or less per sample. 5,6 Using EL images and PL images taken with external control of the voltage to measure lateral variations of the series resistance in silicon solar cells was proposed in Ref. 7. Some preliminary qualitative results were also reported. 7,8 Here, we demonstrate a quantitative determination of the series resistance and its lateral variation in a monocrystalline industrial screen printed silicon solar cell by luminescence imaging. Photoluminescence images are taken using an 815 nm/25 W laser that is expanded to illuminate the cell area of 12.512.5 cm 2 homogeneously with up to 0.67 Sun equivalent illumination intensity. A thermoelectrically cooled silicon charge coupled device camera is used to capture luminescence images. For the PL images with simultaneous current extraction, two arrays of ten spring loaded contact pins are used to contact the busbars of the cell homogeneously. A commercially available instrument is used for Corescan measurements; illuminated IV curves are measured with a calibrated industrial cell tester. In a simplified case, a solar cell is described as a twodimensional network of parallel nodes, with each node consisting of a series connection of a local resistor Rs,i and a diode. The value of R s,i is given as

Spatially resolved series resistance of silicon solar cells obtained from luminescence imaging

This letter introduces a method based on electroluminescence imaging to determine mappings of the local series resistance of large area semiconductor devices such as solar cells. The method combines the local electroluminescence emission Φi(U) and its derivative Φi′(U) with respect to the applied voltage U. The combined analysis of these two quantities yields the local series resistance Rise and proves the physical validity of the used current transport model and thus the physical relevance of the determined Rise value. The method is verified on a monocrystalline silicon solar cell with local shunts and local series resistance problems.

Series resistance imaging of solar cells by voltage dependent electroluminescence

A lithium ion battery electrode includes silicon nanowires used for insertion of lithium ions and including a conductivity enhancement, the nanowires growth-rooted to the conductive substrate.

Electrode including nanostructures for rechargeable cells

A technique for fast and spatially resolved measurement of the effective series resistance of silicon solar cells from luminescence images is introduced. Without compromising the speed of existing luminescence based series resistance imaging methods, this method offers significant advantages in that it is more robust against variations in local diode characteristics. Lateral variations in the series resistance of an industrial screen printed multicrystalline silicon solar cell obtained from this method show excellent correlation with a Corescan measurement and are also shown to be unaffected by lateral variations in the diode properties.

Advanced luminescence based effective series resistance imaging of silicon solar cells

This review is devoted to the analysis of the problems related to fabrication of the Si porous layers. The review was motivated by a great interest to Si-based porous materials from nano- to macro-scale for various applications in electronics, optoelectronics, photonics, chemical sensors, biosensors, etc. The peculiarities of the silicon porosification and the principles of preparing porous layers are considered in the present article. Various methods used for Si porosification such as chemical stain etching, chemical vapor etching, laser-induced etching, metal-assisted etching, spark processing and reactive ion (plasma) etching were analyzed. However, the main attention was focused on electrochemical porosification of Si. The review discusses in detail the influence of parameters such as electrolyte composition and pH, current density, etching time, temperature, wafer doping and orientation, lighting, magnetic field, and ultrasonic agitation on the process of Si porosification. It was shown that the stru...

Silicon Porosification: State of the Art

https://www.tf.uni-kiel.de/matwis/amat/publications/solar_energy_materials_cello/cello_solar_energy_materials_and_solar_cells.pdf

CELLO: an advanced LBIC measurement technique for solar cell local characterization

The device etches semiconductors with a large surface area in a trough-shaped receptacle containing a liquid electrolyte. A sample head is mounted inside the etching trough, and is provided with a device for holding at least one semiconductor wafer. The device is tilted to promote turbulent electrolyte flow in a space between a bottom surface of the semiconductor wafer and top surface of the trough-shaped receptacle.

Device for etching semiconductors with a large surface area

While electrochemical etching of small samples in the 1 cm region is relatively easy, this is not true for large areas, i.e. standard wafer sizes up to 300 mm. The paper outlines the specific demands and difficulties in some detail, discusses large area etching strategies and systems, in particular for very deep macropores, and presents and discusses various results from the large area etching system of the authors. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Large area etching for porous semiconductors

The invention relates to a structure comprising nanowires that extend parallel to each other and that are made of a semiconductor material, the structure having at least one flat side having exposed, regularly arranged nanowires and having at least one macroporous stabilizing layer that is made of the same semiconductor material and that is penetrated perpendicularly by the nanowires, wherein the exposed nanowire ends protrude beyond the stabilizing layer by less than 100 μm.

Nanowire structure having exposed, regularly arranged nanowire ends and method for producing such a structure

Polymers often do not provide all necessary properties for certain applications. In this case polymer composites can be used to combine beneficial qualities of each single component. In many cases, especially for surface–bulk-composites, adhesion is an issue because polymers with complementary properties are necessary. If the chemical binding of the pristine polymers does not allow for good adhesion, advanced strategies have to be employed which most of the time lead to chemical alteration of the surface, its destruction or else low adhesion. While roughening of the surface leads to an increase in the interface area, it will not provide a stable bond, if the adhesion between the two polymers is low in the first place. By selforganized introduction of special undercuts onto one of the polymer surfaces and by applying the second polymer in a liquid form, a mechanical interlocking composite can be achieved. In these composites adhesion can be so strong that only cohesive failure in one of the polymers will occur. In this work we evaluated simple fabrication techniques for the design of simple and complex undercuts and the adhesion between the exemplary composite PEEK and PDMS. We find that by utilizing the capillary effect, spherical standard particles can be used to create a surface structure for mechanical interlocking. Additionally, we obtain a 5.6 times higher adhesion between PEEK and PDMS. We come to the conclusion that a multi-scale undercut is necessary to obtain a strong adhesion between soft polymers like PDMS and stiff polymers like PEEK by looking at the detachment mechanism for these different undercut systems. Lastly, the composite is evaluated by blood contact tests to verify the intactness of the blood repellant effects of the PDMS layer.

Jörg Bahr

Papers

CELLO: an advanced LBIC measurement technique for solar cell local characterization

Device for etching semiconductors with a large surface area

Large area etching for porous semiconductors

Nanowire structure having exposed, regularly arranged nanowire ends and method for producing such a structure

Perfect polymer interlocking by spherical particles: capillary force shapes hierarchical composite undercuts