# Quarterly Technical Status Report change as comment in properties2/11/04 - 5/10/04

NREL Subcontract NDJ-2-30630-24 with *Syracuse University.\
*Deliverable D.3.1 . Submitted: November 13, 2023.

Bolko von Roedern, NREL Technical Monitor; Vicki Riddell, NREL
Subcontract Administrator.

Eric A. Schiff, principal investigator; Rafik Middya, research assistant
professor. Steluta Dinca, Jianjun Liang, Weining Wang, graduate
assistants.

## Hole Drift Mobility Measurements: Amorphous Silicon Cells on Stainless Steel

We are working on techniques for hole drift-mobility measurements in
*pin* cells prepared on stainless steel substrates. Such measurements
have not been reported previously, but could be valuable in
understanding substrate-type solar cells. This work is a collaboration
with United Solar (contact Baojie Yan).

In the standard approach to making hole drift-mobility measurements,
illumination is through the *n-*layer, typically with a 500 nm
wavelength. For the cells on stainless steel, the *n*-layer is the first
layer deposited onto the stainless steel, so illumination from this side
of the cell is not an option. We have been assessing whether we can get
hole drift-mobilities using illumination through the *p­-*layer. We
compare transient photocurrents measured using "green" illumination,
which are sensitive primarily to electron motion, to the measurements
using "red" illumination, which are sensitive to both electrons and
holes. In principle, these data should permit extraction of the hole
properties.

We are experiencing some technical difficulty that can be traced to an
unexpected feature in the "green" (electron dominated) transients. The
measurements are nonetheless promising, and they indicate that intrinsic
layers made with high hydrogen dilution do have larger hole mobilities
than cells incorporating "undiluted" layers.

We have also examined "special" samples made at United Solar on glass.
While hole mobilities on glass substrates are fairly routine to measure,
we don't think these samples have identical properties to those made on
the standard stainless substrate, and we intend to persevere with the
"green/red" approach in the next quarter.

## Modeling and Measurements on a Thickness Series of Cells

We now have a set of temperature (220 -- 350 K) and intensity-dependent
*J-V* measurements on a series of cells made at United Solar with
varying intrinsic layer thickness. The measurements are done using 685
nm laser illumination; the use of monochromatic illumination is
desirable for establishing the electronic behavior of the cells.

We are working on modeling of these measurements using a model based
mainly on hole drift mobilities. This model is working fairly well for
the intensity-dependence. The temperature-dependence modeling is not as
successful; the difficulty may be attributable to a difficulty with AMPS
PC, the modeling program from Penn State that we have been using for
several years. AMPS PC only permits the valence bandtail width to be
chosen in multiples of 10 meV, which is too coarse. We are presently
assessing the ASA program developed by Miro Zeman and collaborators in
the Netherlands.

## Polymer/a-Si:H Heterostructures

We have made some devices with a-Si:H *n* and *i* layers and a
polyaniline-based *p*-layer. The open-circuit voltages obtained are
about 0.7 V at present. We need to improve the series resistance of
these devices, which we expect should be fairly easy to do. We have
already obtained *J-V* curves for polyaniline/

## Drift Mobility Measurements in CIGS Cells

We have started work on mobility measurements in these cells, which were
provided by David Young at NREL. The photocurrent measurements are
promising, but we need to substantially reduce the capacitance of the
test structures. We are working with Young on this now.

## Drift Mobility Measurements in Microcrystalline Silicon Cells

We have reported several times on this project, which is a collaboration
with Thorsten Dylla and Friedhelm Finger of Forschungszentrum Juelich.
Experimental work was finished last summer. In the most recent quarter
we have submitted a short paper to the Spring MRS meeting; a preprint is
available on the web at:

[http://physics.syr.edu/\~schiff/Publications/Hole Drift in
Microcrystalline Si - MRS
S04.pdf](http://physics.syr.edu/~schiff/Publications/Hole Drift in Microcrystalline Si - MRS S04.pdf)

Thorsten Dylla is incorporating these experiments into his doctoral
thesis, and we expect to write further papers based on this work.