Thin-film (non-perovskite) PV modules

Status

Inorganic thin film PV technologies

CIGS and CdTe are mature and commercially available thin film technologies which show lab cell record efficiencies of 23.4 % (11) and 22.1 % (12), respectively, and mini module ef- ficiencies approaching 20 %. Current commercial modules have aperture efficiencies in the range of 13-17 %, and ex- isting production lines also show already today a relatively low carbon footprint per Wp on a module level.

The annual CdTe production is 7-8 GWp (15) while the an- nual production of CIGS was approximately 1.6 GWp in 2019 (16) giving these technologies a market share of 6 % in 2019 (Fraunhofer ISE: Photovoltaics Report, updated: 23 June 2020).

However, economies of scale have not yet been fully ex- ploited, in particular for CIGS.

Factors that currently limit the growth of CIGS and CdTe markets are the efficiency gap between record laboratory devices and production modules, the comparatively low production volume of CIGS compared to crystalline silicon devices and a higher investment risk.

Another concern that is often raised regarding CIGS and CdTe production is the fact that they use comparatively rare elements, regarded as critical raw materials by the Eu- ropean Union.

Currently, a few companies, mainly in Asia, dominate the CIGS market: Solar Frontier, Japan is the largest CIGS pro- ducer, operating factories with 1 GW production capacity, while several Chinese manufacturers are building up pro- duction capacity. Europe has a long-standing track record of high (record) efficiencies and excellent know-how in manufacturing equipment, yet only a few European pro- ducers, mostly branches of Asian companies, are still ac- tive in CIGS production. In the case of CdTe, there is mainly one large producer, namely First Solar in the USA.

An excellent R&D landscape in Europe has built a track record of successfully transferring innovations and effi- ciency improvements into industrial production. European machine and equipment manufacturers are well placed to make Europe again the global leader for thin film tech- nologies and initiate local production capacities, securing high value jobs through manufacturing and supply chain. Several R&D labs and pilot plants of international thin film PV module producers with a deep knowledge in industrial- ization and continuous product development are located in Europe.

Organic PV technology

The technology of Organic Photovoltaics (OPV) has recent- ly achieved the record cell efficiency of 18,2 % (on 0,03 cm2) paved by a staggering 50 % rise in efficiency in the last five years . (18) This is largely due to the introduction of a new class of electron acceptors, the so-called Non-Fuller- ene Acceptors (NFA). Considering the anticipated 100-fold rise in installed PV capacity by 2050, (19) scalable technol- ogies relying on abundant elements with low toxicity and short energy payback will be required, positioning OPV as a green PV technology of the future.

For NFA based OPV, bulk heterojunctions have today reached efficiencies above 18 %, (20) using NFA molecules from the new Y-family, e.g.Y6 (BTP-4F). (21) Besides en- hanced infrared absorption explaining part of the effi- ciency rise for NFA OPV, a large fraction of the improve- ments comes from minimized voltage losses arising from charge generation at nearly zero energy level offsets, at electron donor and acceptor interfaces. The progress can also be linked to improved exciton lifetimes and diffusion lengths in these new NFA systems, compared to the fuller- ene-based electron acceptors, which opens a potential for simpler bilayer donor-acceptor architectures.

The record efficiency for OPV mini-modules currently stands at 13,6 % (on 66,6 cm2), and the typical efficiency of final products is 5–7 %. (22) With the first generation of OPV technology, lifetimes of up to 10 years were achieved un- der outdoor conditions and the cost of products have gone down by roughly a factor of 10 from 10 €/Wp . (23), (24)With upscaling to a GW level technology, costs as low as 5 €ct/ Wp are predicted for OPV

Emerging thin-film technologies

New inorganic materials include chalcogenides (Cu2ZnSn(S,Se)4, Sb2(S,Se)3, CuSbSe2, Cu2SnS3, Bi2S3, PbS etc.), oxides (Cu2O) and pnictides (InP, Zn3P2, ZnSnP2, Zn- SnN2, (In,Ga)N etc.). These technologies do not exist be- yond lab scale but have shown enough development (sta- bility, efficiency >5 % etc.) to identify them as potential future technological solutions:

Record efficiencies:

• Cu2ZnSn(S,Se)4 (CZTSSe) 12.6%
• Sb2(S,Se)3 10.5%
• CuO2 8.1%
• Zn3P2 6.0%

Targets, Type of Activity and TRL

Like Si-PV or Pk-PV single-junction cells and modules, it is required that for all thin-film PV technologies their mod- ule efficiencies will be comparable to current existing PV technologies (module efficiency threshold of 15 %) within 5 years. At the same time, thin-film PV module manufac- turing should quickly achieve comparable costs compared to currently commercial technologies.

Mature thin-film technologies

For CdTe and CIGS, the main challenge will be to increase the production volume to profit from the scaling effects. Furthermore, the gap between laboratory devices and commercial modules has to be closed to reach competitive efficiencies and thus LCOE comparable to or better than for c-Si. Another challenge is to ensure the supply of criti- cal raw materials like indium, gallium or tellurium to a mul- ti-terawatt industry.

OPV

The main challenges are increasing efficiency for large ar- eas (threshold of 15 %) and further increasing long-term stability. Since OPV will initially mainly serve (indoor) niche markets, the stability criterion is less severe than for stand- ard outdoor modules.

Kesterites

Kesterite technology is sufficiently mature compared to other emerging TF PV (TRL 5-6) and continues to evolve from its current mini-module configuration towards fur- ther industry upscaling. The aim is to demonstrate within 5 years that this TF PV technology can reach the threshold of 15 % (both cell and module) to be considered for the market under solid competitiveness arguments (reduced manufacturing cost, short energy payback time of less than 1 year, sustainability, long lifetime, high yield, excel- lent properties for BIPV, PIPV applications) with mature TF PV technologies

Other emerging materials

Here, more fundamental problems have to be solved, above all the low efficiency of devices based on most of these materials. Here, more basic research is needed to overcome some of the observed barriers.

Early-Stage Research Actions (TRL2-3)

CIGS

• Implementation of completely dry processing in- cluding surface cleaning after post-deposition treat- ment (PDT)
• Implementation of selective contacts in CIGS solar cell structures instead of band grading
• Improving the thermal stability of CIGS low band gap devices for applications in monolithic tandem devices

Organic PV technology

• Modelling and prediction of new organic materials combinations for polymer and small molecule or- ganic solar cells
• Establish the coupling between morphology and functionality for both fullerene and non-fullerene acceptor materials and determine the principles for realising these with scalable processing methods
• Explore the possibilities of leveraging strong light-matter coupling with highly ordered non-fuller- ene acceptors, to realise simpler bi-layer structures for more stable, efficient organic solar cells
• “Simple” materials, like non-fused ring systems, or, to some extent single composites materials (SCOSC) for improved stability
• Organic semiconductors and semiconductor inks that are fully compatible with environmental and green processing
• Develop generic concepts for doping of organic semiconductors

Emerging thin-film technologies

• Novel thin-film absorber materials for reduced en- ergy and material costs, including everything offer- ing more yield
• High-throughput materials research in combination with simulation and Artificial Intelligence to identify new promising materials suitable as absorber or as other functional layer
• Search for high band gap absorbers

Development Research Actions (TRL 3-5)

Inorganic thin film technologies

CIGS

• Increased consideration of sustainability: environ- mental impact, resource availability, recyclability, energy balance
• Exploit thin-film advantages such as the possibility of flexible and lightweight modules, semi-trans- parent modules, and control of size and shape of modules to open up new markets in the field of in- tegrated PV
• Reducing the amount of active material in CIGS technology

Organic PV technology

• Interface and charge extraction layers for OPV, forming long time stable contacts
• Other alternative architectures including bilayer, graded bilayer, ultrathin layer OPV
• Lamination and packaging processes that can oper- ate below 140 ° C compatible with roll-to-roll OPV processing
• High-quality barrier layers and in situ packaging, thin-film solution processed packaging for im- proved stability and longevity

Emerging thin-film technologies

• Develop and apply standardized/commonly ap- proved material assessment approaches to carrier lifetime, characterisation of surface recombination, bandgap and possible degradation/change of these parameters
• Accelerated incorporation of concepts for perfor- mance improvements developed for traditional thin-film technologies (e.g. interface treatments, grain boundary passivation, etc.) to emerging TF PV technologies

Demonstration Actions (TRL 5-7)

CIGS

• Realisation of in-line characterisation for process control utilizing digitalisation, machine learning tools and IoT concepts
• Mass customized BIPV laminates with various col- ours, transparencies and sizes fully compatible with classic facade elements

Organic PV technology

• High resolution patterning processes for OPV with feature sizes of 100 micron or lower
• Production processes for “Mass Customization” according to specific requirements for format and shape for integrated PV like BIPV or vehicle-inte- grated PV

Flagship Actions (TRL7-8)

• Develop next generation production equipment for larger size modules, high yield and throughput and low energy and material consumption to leverage economies of scale and improve the environmental footprint for CIGS and CdTe thin film module pro- duction
• Production processes and equipment for “Mass Customization” according to specific requirements for format and shape for integrated PV like BIPV or vehicle-integrated PV (high TRL)

KPIs

In 2030, there should be a strong position of mature thin film, non-perovskite PV in the market due to the specific ad- vantages thin film technology possesses. For 2030 European non-Pk thin-film PV R&D should achieve the following KPIs: