The Bridge - Issue 3, 2020 - 6

THE FUTURE OF RENEWABLE ENERGY GENERATION:

Photovoltaic Materials
Annalise Maughan, Kai Zhu, and Joseph J. Berry

Intro to Photovoltaics (PV)
There are myriad ways to harness solar energy,
including, but not limited to: solar thermal, solar
fuels, and photovoltaics (PV). Across the portfolio
of solar energy technologies, PV is unique in that
collected photons are directly converted to electricity.
Traditionally, the dominant materials in PV are also
the dominant semiconductor and optoelectronic
materials. The cost of solar energy from PV is a
product of a complex combination of non-material
related factors, known as soft costs, e.g., permitting,
zoning, and of balance-of-systems (BOS) costs, like
inverters or other components needed to utilize
cells and modules. While the soft costs are due to
administrative/regulatory concerns, BOS costs are

driven by details of cell/module fabrication, mounting,
power electronics, and other concerns, which touch
on a range of basic material science issues. There
is some overlap of BOS and soft cost, as a lighter
weight solar panel can reduce installations costs, as
an example. At the PV-system level, the materials
considerations span both electronic and structural
components. The focus of this paper is the solar cell,
which is the minimum operational unit device that
converts light into electricity.

Typical solar cells are sophisticated stacks of
semiconductors, as shown in Figures 1 (a) and (b),
with an electronic structure, which is prototypically
for a PV shown in panel (c). The primary absorber
material that defines the various technologies must
have a critical combination of
properties. The absorber must
interact strongly with light, i.e.,
have high absorption, and
have good transport properties
to ensure that photogenerated
carriers can be efficiently
extracted before they are
Figure 1: Typical thin film solar cell configuration is shown in figure (a). Panel (b) shows structure
lost to internal nonradiative
common to single crystal III-V or Si systems. In both cases, the orientation of electron and hole selective
recombination. The broadband
contacts can be changed. In the case of configuration (a), the device fabrication can be undertaken on
glass/metal or metal foil rather than a transparent substrate. Panel (c) shows the energy band diagram
solar spectrum creates a
for a typical PV device configuration, with phonon/thermal loss when photon energy is greater than the
premium on having the
energy/bandgap. Other loss mechanisms associated with bulk or interface recombination are not shown.

THE BRIDGE

https://hkn.ieee.org/ https://hkn.ieee.org/

The Bridge - Issue 3, 2020

Table of Contents for the Digital Edition of The Bridge - Issue 3, 2020