John I B Wilson & Robert R MatherPower Textiles Limited

Photovoltaic Solar Textiles

Contents

• Features of a photovoltaic (PV) cell

• Reason for using textiles

• Fabrication of PV cells on textiles

• Problems to solve

From here

to here

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Features of a PV cell

Sandwich structure: an active semiconductor between two electrical contacts

Semiconductor absorbs light to give electrical charges

Electric field within two-layer semiconductor separates +/- charges

Contacts deliver current to load

Cells are connected together to increase voltage and current

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PV performance parameters• Current increases with light intensity• Voltage falls with temperature• Shading reduces current• Power output depends on load resistance

• “standard test conditions” 1kW/m2, AM1.5, 25oC

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Light intensity

Output power, P = V x I

Current, IPower, P

Voltage, V00 Voc

Isc Pmax

PV materials

Commonly rigid Si crystalBut thin-film options:

• a-Si:H• CdTe• CIS, CIGS• perovskites• kesterites (CZTS)• organics (including polymers)

• Dye sensitized solar cells• III-V’s

Mitsubishi

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Organic PV, Frauenhofer ISE

CIGS PV

Absorption spectrum to match illumination

Perovskite, Microquanta

Why textiles as PV substrates

• Two contrasting applications: • small scale wearables et al• large scale awnings, shades, covers

• Flexible• Shapeable• Lightweight• Low embedded energy (only one third

or less than energy in glass substrates)

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Considerations for fabricating PV on textiles

• active area (porosity)

• thin and conformal layers (texture)

• electrical conduction (structural/dimensional stability)

• maximum temperature (material choice)

• stability in vacuum/plasma/uv(processing)

• transparency (substrate/superstrate)

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Electronics/Semiconductors AND Textile industry compatibility:

Attach completed PV to fabric - simple but hinders fabric behaviour & aesthetics

OR

PV-coated fibre – avoids texture restrictions of fabric but difficult to weave

OR

PV-coated fabric – avoids topology demands of cell connections but uneven surface

Addressing the process conditions for DSSC:inserting Dye Sensitized Solar Cells into fabric (glass fibre)

Ju Yun, M. et al, Sci. Rep. 5, 2015, 11022

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Addressing the electrical conductor problem: both fibre and sheet coating (organic PV)

C. Wu et al, Nano Energy, 2017, 32, 367-373.

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Textile fibreCathode

PV active materialAnode

Each long thin cell must be connected at anode and cathode

and cells must not short circuit at cross-overs

Fibre PV topology: many connections

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Addressing the textured surface:dip-coated resin on glass fibre bundles (amorphous Si)

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J. Plentz et al Mater. Sci. Eng. B 2016, 204, 34–37

ZnO:Al

butadiene styrene methacrylateon glass fibres

PV textiles

• Material: glass fibre, polyimide, polyester, nylon, PTFE, …

• construction: woven, non-woven, knitted, …

• PV material: organics, perovskites, DSSC, a-Si:H

• process methods: dip, spray, spin, screen print, blade coating, inkjet, CVD, …

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Types of fabric

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knitting – less stable structure

non-wovens – very porousweaving – many options for pattern and yarn shape

plain weave – multi-filament, polyester

“The Solar Textile Challenge: How It Will Not Work and Where It Might” :aligning tapes of small cells to form a solar textile

F. C. Krebs and M. Hcsel, ChemSusChem 2015, 8, 966 – 969 15

Zhang et al, Adv Mats 28, 2016, 263-9

Addressing the friction of weaving coated yarn:warp conductors, weft DSSC photoanode layers

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(absorber layer is shadowed by counter electrode at crossover points)

delicate structure for DSSC layers: ZnO nanowires

Min Ju Yun et al Scientific Reports 6, 2016, 34249

Addressing the friction of weaving coated yarn:warp conductors and insulators, weft glass yarn, post-coated DSSC layers

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TiO2 paste added after weavingto avoid friction damage by loom;electrolyte filled afterwards

Addressing the textured porous surface:screen-printed levelling layer for DSSC on woven glass fibre

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Surface smoothed with screen printed liquid polyimide

and screen-printed Ag;

spray coating, drop casting, and screen printing for other layers.

NB high temp curing for TiO2 (450oC) restricted the choice of fabric.

Jingqi Liu et al, Scientific Reports (2019) 9:1362

Addressing the temperature limitation:spray-coated organic PV on woven polyester cotton

press Ag NW to flatten interface and prevent s/c

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S. Arumugam et al, J. Mater. Chem. A, 2016,4, 5561-5568

Repeat for each layer

Addressing roughness and process issues:solution processed organic PV on woven polyester cotton

All solution processed (mostly spray-coated), 1.23% efficiency.

20S. Arumugam et al, IEEE journal of photovoltaics 8, 2018 , 1710-1715

“The fabrication processes are fully scalable and can be readily adapted into a standard textile manufacturing process line…”

AgNW: 100 nmPEDOT:PSS: 50 nm P3HT:ICBA: 200 nmZnO-NP: 400 nm Ag: 200 nm

Addressing the yarn movement and texture in woven fabric:PECVD silicon on woven polyester

Uncoated woven polyester

PEDOT:PSS coated

Aluminium over PEDOT:PSS

Silicon on Al on PEDOT:PSS1 mm

LP PECVD: 200oC

Evap or sputter

Doctor blade

calendered: 220oC

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Thin-film silicon deposition by RF PECVD: low temperature conformal deposition

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Low pressure reactive gas mixtures;Temperature must be at least 200oC so polyester suitable; Plasma generates active atomic H which can react with some surfaces;Must degas and dry substrates before plasma on.

Addressing aesthetics:colour and flexibility

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any shape or size of cell

150mmBut efficiency <1%on polyester now…

Problems to solve, but some solutions

• Conducting layer continuity and integrity

• Conformality of thin layers

• ITO brittleness

• Encapsulation (durability)

• Integrated fabrication

• Scaling up in area

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Fabric Substrate

Polymer

Aluminium film

Bubbles

Hatched bubble

Un hatched bubble

Fabric substrate

polymer

Aluminium

a-si:HTCO

Gas expand

PECVD & 200oC

Short circuit

Short circuit

A. Diyaf, PhD thesis, Heriot-Watt University, 2013

Problems with conformality, and defects in liquid coating

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Thin-film silicon layer is short-circuitedif there are residual gas bubbles in liquid polymerthat will expand during later processing;

Similar short-circuits arise where silicon is too thin,perhaps at masked edges.

Problem with durability: effective encapsulation

Substrate

Base polymer

Oxide

Polymer

Oxide

Polymer

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A. Uddin et al, Coatings 9, 2019, 65

efficient diffusion barrier needed for water vapour and oxygenas these cause degradation in organics and perovskites:transmission rates should be< 10−3–10−6 g·m−2·day−1 and <10−3–10−5 cm3·m−2·day−1·atm−1

and also block UV.

provide with multi-layer thin-films (eg atomic layer deposition for inorganicand CVD for polymer) so any pinholes do not alignlamination or liquid coating preferred, if improved.

Proven flexibility: organic PV with improved contacts optimising conductivity, transmission, and smoothness – BUT not on textile

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PEDOT:PSS PH1000 doped with ethylene glycol (EG)

Best result 10.3% efficiency

T. Lei et al, J. Mater. Chem. A, 2019, 7, 3737–3744

Moving towards large area fabrication:slot-die printing of flexible organic solar cells on polymer sheet

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~1% less in efficiency for 15.00 cm2 areaBUT not on textile

X. Meng et al, Adv. Mater. 2019, 31, 1903649

Acknowledgements

J&D Wilkie, Kirriemuir, for polyester.

Former students who have worked on our flexible cells:

Suzanne JardineHelena LindAdel DiyafArtem Lukianov

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