Copper Indium Gallium Selenide (CIGS) Nanowires for Photovoltaic Applications

::Download Scientific Description::  ::Project Researchers and Highly Qualified Personnel::  ::Project Progress Summary::  ::Project Scientific Progress::  Currently, thin film solar cells based on CIGS absorbers (p-CuIn1-xGaxSe2) are among the most attractive solutions for photovoltaic (PV) applications. A number of companies offer such modules commercially and reported cell efficiencies have reached ˜20%. Moreover, such CIGS cells are predicted to be capable of achieving efficiencies of ˜30%, while offering the benefits of good stability and relatively low manufacturing cost.

However, CIGS cells suffer from a number of problems which are limiting their current performance. Many of these problems are related to the fact that the CIGS thin-film solar cells are not composed of a single crystalline material but rather, “grains” of differing crystal orientations connected together with problematic effects occurring at grain boundaries.

There exists different approaches to overcoming these issues but in this project, we are examining approaches based on nanowires. A nanowire film looks “hairy” because it is composed of many tiny “wires” that extend upwards as opposed to being uniformly flat. This material structure has several advantageous that may help enhance light absorption. One major advantage is that the small dimensions of nanowires can reduce strain in the material, making it easier to for them to form as a single crystal. This can then alleviate the deleterious grain-boundary effects associated with uniformly flat films.

There still needs to be much work in determining the optimal growth conditions for CIGS nanowires and that is where our research begins. We plan to study the conditions for the preparation of CIGS nanowires having different alloy composition and dimensions and correlating this with optical and conduction properties on single nanowires obtained from various methods including steady state, dynamic photocurrent and photovoltage spectroscopy. This experimental work will be contrasted with electronic property calculations from Density Function Theory (DFT) and Tight Binding (TB) methods.

We will also study the conditions required to infiltrate CIGS nanowires with AZO (ZnO:Al) and characterize the optical and electrical characteristics of such hetero-junctions. The motivation here is that the CIGS/AZO hetero-junction moves us closer to an actual nanowire photovoltaic device. In particular, an important objective is to establish the role of deleterious interfacial effects, charge separation and conduction, using temperature dependent measurements. We will consider various approaches to ameliorating these effects including buffer layers and annealing/passivation methodologies. Achieving these objectives will provide the knowledge required to design CIGS nanowire – AZO based structures suitable for consideration for next generation solar cells for our industrial partner, Prised Solar.