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Felder 1
Jenny Felder
Mentor: Chris Kenney
Project: High-Voltage Photovoltaic Cell Fabrication
1) What is the normal voltage of photovoltaic cells
2) What are the advantages of high-voltage
3) What is the efficiency?
4) Will you have time to test them?
My project consists of fabricating a high-voltage photovoltaic cell. This PV
cell will be fabricated on float-zone silicon wafers. There are three main phases of
the project: designing the mask to be used in fabrication, fabricating the actual
device, and testing the functional device. I am currently working on the first phase
of the project, the design of the mask to be used in fabrication. The computer
software ‘Layout’ is being used to design the mask.
In beginning the design process, a list of features necessary for the PV cell
was first developed. These features were divided into two categories, fabrication
test features and device features. The purpose of the fabrication tests included in
the design was to verify the following aspects of the device: the conductivity of the
metal, the conductivity the N and P diffusion layers, the contact between both the
metal and N diffusion layer and the metal and P diffusion layer, diode functionality,
trench hopping and the FOX etch and glass etch patterns. Each of these aspects
required a separate fabrication feature; this was important because they allow the
various properties of the device to be tested independently of one another. In this
way, if the PV cell does not work properly after fabrication, it will be relatively
easier to pinpoint which feature is not functioning properly and to diagnose and fix
the problem.
Once the fabrication test features are designed, the design of the actual PV
cell device will be developed. High voltage PV cells will be designed having
dimensions of both 50 m and 100 m squares. The design of the PV cells will also
be varied to produce different output voltages, ranging from 50 V to 2000 V.
Different layouts of the cells themselves will also be considered, including the most
simple, linear design, as well as circular or hexagonal designs. In addition, several
features will be added to the PV cell. These include the ability to bypass a particular
diode, connections for external switches, and side-entrance photo switches.
After the design phase of the project, the next step will be to actually
fabricate the device. This will be done at the Stanford Nanofabrication Facility, on
campus. The third, and final, stage of this project is to test the final device after
fabrication. Once the PV cells are fabricated on the silicon wafers, the wafers will be
cut up to produce individual PV cells (as many cells will fit on a single wafer). The
output voltage of each cell, the efficiency, as well as other factors will be measured
to assess the utility of the device as a power supply.
This project has several important implications. First, at SLAC in particular it
can be implemented as a more efficient, smaller power supply for the EXO
experiment. However, it has larger applications outside of this facility as well. Such
devices could be implemented on a larger scale as an alternative energy source,
which could have many important positive effects on society.