Copper indium gallium selenide solar cell
CIGS outperforms polysilicon at the cell level, however its module efficiency is still lower, due to a less mature upscaling.
[2] CIGS cells continue being developed, as they promise to reach silicon-like efficiencies, while maintaining their low costs, as is typical for thin-film technology.
To reach the ideal bandgap for a single junction solar cell, 1.5 eV, a Ga/(In+Ga) ratio of roughly 0.7 is optimal.
[18] The Al doped ZnO serves as a transparent conducting oxide to collect and move electrons out of the cell while absorbing as little light as possible.
The CuInSe2-based materials that are of interest for photovoltaic applications include several elements from groups I, III and VI in the periodic table.
[20] A team at the National Renewable Energy Laboratory achieved 19.9%, a record at the time,[21] by modifying the CIGS surface and making it look like CIS.
In 2013, scientists at the Swiss Federal Laboratories for Materials Science and Technology developed CIGS cells on flexible polymer foils with a new record efficiency of 20.4%.
A direct bandgap material, CIGS has very strong light absorption and a layer of only 1–2 micrometers (μm) is enough to absorb most of the sunlight.
[citation needed] The active CIGS-layer can be deposited in a polycrystalline form directly onto molybdenum (Mo) coated on a variety of several different substrates such as glass sheets, steel bands and plastic foils made of polyimide.
[30] In the highly competitive PV industry, pressure increased on CIGS manufacturers, leading to the bankruptcy of several companies, as prices for conventional silicon cells declined rapidly in recent years.
CIGS and CdTe-PV remain the only two commercially successful thin-film technologies in a globally fast-growing PV market.
[citation needed] In photovoltaics "thinness" generally is in reference to so-called "first generation" high-efficiency silicon cells, which are manufactured from bulk wafers hundreds of micrometers thick.
In 2008, CIGS efficiency was by far the highest compared with those achieved by other thin film technologies such as cadmium telluride photovoltaics (CdTe) or amorphous silicon (a-Si).
In 2015, the gap with the other thin film technologies has been closed, with record cell efficiencies in laboratories of 21.5% for CdTe (FirstSolar) and 21.7% for CIGS (ZSW).
[34]) The most common vacuum-based process is to co-evaporate or co-sputter copper, gallium, and indium onto a substrate at room temperature, then anneal the resulting film with a selenide vapor.
[citation needed] A non-vacuum-based alternative process deposits nanoparticles of the precursor materials on the substrate and then sinters them in situ.
Companies currently that used similar processes include Showa Shell, Avancis, Miasolé, Honda Soltec, and Energy Photovoltaics (EPV).
The advantages of this process include uniformity over large areas, non-vacuum or low-vacuum equipment and adaptability to roll-to-roll manufacturing.
[citation needed] Nanosolar reported a cell (not module) efficiency of 14%, however this was not verified by any national laboratory testing, nor did they allow onsite inspections.
Related to these issues, the film had poor transport properties including a low Hall mobility and short carrier lifetime.
Boeing's coevaporation process deposits bilayers of CIGS with different stoichiometries onto a heated substrate and allows them to intermix.
[citation needed] NREL developed another process that involves three deposition steps and produced the current CIGS efficiency record holder at 20.3%.
[12] Würth Solar began producing CIGS cells using an inline coevaporation system in 2005 with module efficiencies between 11% and 12%.
These films performed quite favorably in relation to other manufacturers and to absorbers grown at NREL and the Institute for Energy Conversion (IEC).
This is evidence of a poor CIGS/CdS interface, possibly due to the lack of an ODC surface layer on the Global Solar film.
[citation needed] Disadvantages include uniformity issues over large areas and the related difficulty of coevaporating elements in an inline system.
Additionally, coevaporation is plagued by low material utilization (deposition on chamber walls instead of the substrate, especially for selenium) and expensive vacuum equipment.
Potential manufacturing problems include difficulties converting CVD to an inline process as well as the expense of handling volatile precursors.
The technique involves the electric field assisted spraying of ink containing CIS nano-particles onto the substrate directly and then sintering in an inert environment.
[43] Concepts of the rear surface passivation for CIGS solar cells shows the potential to improve the efficiency.
