Analysis of the Effects of Impurities in Silicon

A solar cell fabrication and analysis program was conducted to determine the effects on the resultant solar cell efficiency of impurities intentionally incorporated into silicon. The program employed flight quality technologies and quality assurance to assure that variations in cell performance were due to the impurities incorporated in the silicon. The initial verification runs have resulted in an average AM0 cell efficiency of 12.8% at 25 C

Radiation tolerance of vertical junction solar cells

Extensive radiation testing of vertical junction (VJ) solar cells demonstrated a radiation tolerance better than both planar silicon cells and at least one type of (AlGa)As-GaAs cell. Due to tradeoffs between short circuit current and open circuit voltage, the end of life (10 to the 16th power 1 MeV electrons/sq cm) maximum power point is nearly independent of bulk resistivity between 2 and 10 ohm cm, increases slightly with increasing wafer thickness between 3 and 11 mils, and increases slightly with increasing groove depth between 1 and 3 mils

Short-circuit current improvement in thin cells with a gridded back contact

The use of gridded back contact on thin silicon solar cells 50 micrometers was investigated. An unexpected increase in short circuit current of almost 10 percent was experienced for 2 cm x 2 cm cells. Control cells with the standard continuous contact metallization were fabricated at the same time as the gridded back cells with all processes identical up to the formation of the back contact. The gridded back contact pattern was delineated by evaporation of Ti-Pd over a photo-resist mask applied to the back of the wafer; the Ti-Pd film on the controls was applied in the standard fashion in a continuous layer over the back of the cell. The Ti-Pd contacts were similarly applied to the front of the wafer, and the grid pattern on both sides of the cell was electroplated with 8-10 micrometers of silver

Process Research On Polycrystalline Silicon Material (PROPSM)

Performance limiting mechanisms in polycrystalline silicon are investigated by fabricating a matrix of solar cells of various thicknesses from polycrystalline silicon wafers of several bulk resistivities. The analysis of the results for the entire matrix indicates that bulk recombination is the dominant factor limiting the short circuit current in large grain (greater than 1 to 2 mm diameter) polycrystalline silicon, the same mechanism that limits the short circuit current in single crystal silicon. An experiment to investigate the limiting mechanisms of open circuit voltage and fill factor for large grain polycrystalline silicon is designed. Two process sequences to fabricate small cells are investigated

Process Research On Polycrystalline Silicon Material (PROPSM)

The mechanisms limiting performance in polycrystalline silicon was determined. The initial set of experiments in this task entails the fabrication of cells of various thicknesses for four different bulk resistivities between 0.1 and 10 omega-cm. The results for the first two lots are presented

Coplanar back contacts for thin silicon solar cells

The type of coplanar back contact solar cell described was constructed with interdigitated n(+) and p(+) type regions on the back of the cell, such that both contacts are made on the back with no metallization grid on the front. This cell construction has several potential advantages over conventional cells for space use namely, convenience of interconnects, lower operating temperatures and higher efficiency due to the elimination of grid shadowing. However, the processing is more complex, and the cell is inherently more radiation sensitive. The latter problem can be reduced substantially by making the cells very thin (approximately 50 micrometers). Two types of interdigitated back contact cells are possible, the types being dependent on the character of the front surface. The front surface field cell has a front surface region that is of the same conductivity type as the bulk but is more heavily doped. This creates an electric field at the surface which repels the minority carriers. The tandem junction cell has a front surface region of a conductivity type that is opposite to that of the bulk. The junction thus created floats to open circuit voltage on illumination and injects carriers into the bulk which then can be collected at the rear junction. For space use, the front surface field cell is potentially more radiation resistant than the tandem junction cell because the flow of minority carriers (electrons) into the bulk will be less sensitive to the production of recombination centers, particularly in the space charge region at the front surface

Bibliographieren – ... aber wie?

Bibliographische Angaben dienen zwei Zielen: Sie sollen die verwendete Literatur zweifelsfrei identifizieren und sie dadurch (wieder-)auffindbar machen, und sie sollen jede direkte und indirekte Übernahme fremden geistigen Eigentums eindeutig als solche kennzeichnen und die verwendeten Quellen offen legen. Beides ist unabdingbar für korrektes wissenschaftliches Arbeiten. Diese Anleitung versteht sich weniger als eine (fachspezifische) Vorschrift – schon gar nicht als die einzig Richtige! – sondern vielmehr als eine allgemeine Einführung in die Prinzipien des Bibliographierens, anhand derer man sich seinen eigenen Stil erarbeiten kann, der für die eigenen Belange angemessen und praktisch ist. Wichtiger als das sklavische Festhalten an bestimmten Formatierungsvorschriften ist es, ein klares, einheitliches und eingängiges Schema zu verwenden, das alle wichtigen Informationen zur Verfügung stellt und auch in seiner Systematik für Dritte verständlich ist

Thin cells for space

Research and pilot line production efforts directed towards the fabrication of high efficiency ultrathin silicon solar cells (50 micrometers) are reported. Conventional ultrathin cells with air-mass-zero (AM0) efficiencies exceeding 14% and coplanar back contact cells with AM0 efficiencies up to 11.7% were developed. The primary mechanisms limiting efficiency were determined in both types of cells, and they are discussed within the context of further improving efficiency. Results of pilot line production of conventional ultrathin cells are also presented. Average AM0 efficiencies of 12% were readily achieved for 2000 cell production runs

PVMaT improvements in the Solarex photovoltaic module manufacturing technology: Annual subcontract report: May 5, 1998 -- April 30, 1999

This report describes work done by Solarex during the first year of this subcontract. The objective of this three-year PVMaT program is to continue the advancement of Solarex PV manufacturing technologies to design and implement a process that produces polycrystalline silicon PV modules that can be sold profitably for $2.00 per peak watt or less and that will increase the production capacity of the Frederick plant to at least 25 megawatts per year. Accomplishments during the first year of the program include: (1) Verification of the process to produce SiF{sub 4}, the precursor to silicon feedstock. (2) Design of a silicon feedstock pilot facility using the SiNaF process. (3) Development of and transfer to manufacturing of a process to use thinner wire in the wire saw. (4) Completion of a production trial with recycled SiC. (5) Laboratory development of a selective emitter process using rapid thermal processing. (6) Fabrication of high-efficiency polycrystalline cells using silicon nitride from three different sources. (7) Development of a new encapsulation formulation and laboratory demonstration of a 6-minute lamination cycle. (8) Implementation of an automated laminator. (9) Laboratory demonstration of automated handling of ceramics

Module Technology: Current Practice and Issues

PV modules must provide mechanical support for the cells, protect the world from the voltages inside, protect the cells, diodes and interconnects from the weather outside, couple as much light as possible into the PV cells and minimize the temperature increase of the cells. The package must continue to serve these functions for at least 25 years as that is the typical module warranty period today. Furthermore the package must do all this for as low a cost as possible since the key to large scale PV growth is a reduction in cost while retaining excellent module reliability and durability. This paper will review current module construction practices for both crystalline silicon and thin film PV with emphasis on explaining why the present designs and materials have been selected. Possible long term issues with today's designs and materials will be discussed. Several proposed solutions to these issues will be presented, highlighting the research efforts that will be necessary in order to verify that they can cost effectively solve the identified issues