1

Reel-to-reel wet coating by variation in solvents and compounds of

photoactive inks for polymer solar cell production

Mario Schrödner a, Steffi Sensfuss

a, Hannes Schache

a, Karin Schultheis

a, T. Welzel

a, K.

Heinemann a, R. Milker

b, J. Marten

b, Lars Blankenburg

a,*

a) Thüringisches Institut für Textil- und Kunststoff-Forschung e.V. (TITK), An-Institut der Technischen Universität Ilmenau, Breitscheidstraße 97, 07407 Rudolstadt (Germany); b) POLY-CHEM AG, Chemiepark Bitterfeld-Wolfen, OT Greppin, Farben-straße, Areal B, 06803 Bitterfeld-Wolfen (Germany) * Corresponding author. Tel.: +49-3672-379558; Fax: +49-3672-379379. E-mail address: blankenburg@titk.de (L. Blankenburg)

Abstract

In this paper we report about progress in reel-to-reel (R2R) solvent-based production of

polymer solar cells. To be aware of the huge advantages in energy and material saving

the hole-injection and the photoactive layer were successfully prepared by continuous

slot-die wet coating of low viscosity inks. It was aimed to reach higher values of light

power conversion efficiencies for reducing the gap between production under best

laboratory conditions on rigid substrates in comparison to more robust large-scale

coating in practice. For this, solvent systems and photoactive materials (electron-

acceptor) were varied and applied with 1 m/min at the laboratory R2R-coating machine

and coating width up to 8 cm. Polymer solar cells (PSCs) manufactured out of the so

coated foils reach in maximum 3.2 % light power conversion efficiency (AM1.5) In this

context, also reel-to-reel wet coating with [6,6]-phenyl-C61-butyric acid methyl ester

(PCBM) systems with change to non-halogenated inks were successfully done for

learning technological suitability and optionally future transfer to the “new” system.

Keywords: reel-to-reel, organic photovoltaics, polymer solar cells, wet coating, slot die

coating

2

1. Introduction

Organic photovoltaics (OPV), particularly with regard to polymer solar cells (PSCs),

that are producible out of solution, is more than ever in focus of research.[1-3] With the

development of new materials for PSCs photoactive layer - light absorbing polymers[4-7]

as well as electron-accepting fullerenes[8-12] - and with actually reached performances

with more than 8 % to 10 % light power conversion efficiency[13,14] the potential for

competition with inorganic thin film PV is given. At the moment the focus of research

is on new low-bandgap polymers[15-21] to increase and broaden the light absorption in

sun spectrum. But also more practical and technological approaches come now on

top.[22] To take care of the competitive advantages there is at present a huge interest to

realize PSCs on flexible substrates[13-27], to produce without indium-tin-oxide (ITO)[28-

31], because of the ITO-availability and the high costs[32], and to develop high-barrier

materials (optically transparent and mechanically flexible)[33,34] to avoid the degradation

of the sensitive organic compounds caused by environmental influences and hence to

ensure longer lifetime of PSC modules. An important feature is the production process

itself. It is aimed to establish reel-to-reel (R2R) processes[35-37] by using up-scaling

techniques out of solution[38,39] like slot-die coating[40,41], brush painting[42] or gravure

printing[43,44] for example.

In own very first experiments in R2R coating modus feasibility could be demonstrated

with only one solvent for photoactive layer formation and small coating width.[36] To

establish a more stable coating process with higher throughput (coating width) it was

now intended to check at the one hand alternative useful solvents and solvent-mixtures

as well as new materials at the other hand for increasing performance of resulting PSC

in production line. With this motivation we report our results in producing PSC, in

which two functional layers, the hole-conducting and the photoactive one, were

3

successfully prepared by continuous R2R wet coating of low viscosity solutions and

dispersions on ITO-coated PET substrates. In this article we summarize our

investigations made on a small-scale coating machine (LBA-200) using R2R-slot-die-

coating technique (Fig. 1), knowing about their beneficial potential to fulfill future

industrial production requirements. The chosen technology convince with features like

continuous coating, low temperature process (energy saving), large-area-coating (2 m

coating width and web speeds up to 600 m/min in principle), pre-metered volume flow

avoids dissipation of material (resources saving) and enables exactly adjustable layer

thickness control (concentration, delivery flow rate, web speed, coating width),

homogenous layer thicknesses are as much achievable as dry layer thicknesses < 1 µm,

because of ability to apply low viscosity and low concentrated inks, only to name some

of the advantages.[45-47]

All of the here described PSCs are fabricated according to the commonly used concept

of bulk heterojunction (BHJ), i.e. blending of polymeric electron-donator with fullerene

-acceptor in the photoactive layer.[48-51]

Halogenated solvents are widely used in PSC production because of combining best

solubility properties for usual light absorbing polymers and electron-accepting

compounds with good film forming behavior, meaning also effective nanophase-

separation[52] in drying process to give finally good power conversion efficiencies. In

general, chlorobenzene and 1,2-dichlorobenzene are the solvents of choice for dis-

continuous spin-coating on rigid ITO-glass substrates for top PSC.[53] However, in tech-

nological and industrial issues it is tried to replace such solvents by non-halogenated

ones because of environmental (toxicity) and aggressive properties against technical

equipment and machines[54,55]. In the work described here, we tested as one issue

halogen-free o-xylene in comparison to the halogenated standard systems in R2R modus

for optional later transfer to best working photoactive systems, what was applied R2R

4

as the second item. Here the common fullerene is replaced by the best state of the art

material. For this system the continuously coating behavior (like wetting, drying) was

studied for showing that even on flexible foils higher PSC efficiencies become possible

for reducing the discrepancy between preparation under ideal conditions in lab in

comparison to production with robust and more industrial profitable needs.

2. Experimental

2.1 Materials

Regioregular poly-3-hexylthiophene (P3HT, OS2100) was purchased from Aldrich and

used as received. [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) was obtained

from Solenne. Bisindene-C60 was synthesized according to He et al.[56] Plexcore

PV2000 system was obtained from Plextronics. All the photoactive solutions were

filtered before use. PEDOT:PSS (poly(3,4-ethylene-dioxythiophene):polystyrene-

sulfonate) was obtained from Heraeus Clevios GmbH (Clevios PH and 4083) and was

filtered prior to use.

ITO coated glass was purchased from Merck (13 Ωsq) and ITO-PET foil (125 µm thick,

40 m, different width) from Southwall. The ITO thickness was 100 nm and the surface

resistance 50 Ωsq.

2.2. Methods

Surface energies were determined with a Krüss contact angle/ surface tension measuring

instrument DSA100. The thicknesses of the films were determined by a Woollam

spectral ellipsometer M44 (600-1200 nm); surface visualization was made by AFM with

the Standard Level AFM (ANFATEC Instruments AG; Oelsnitz; scan: 30 µm, lateral: <

5 nm, z: < 0.5 nm). For measurements of light transmission a Thermo Spectronic

5

UNICAM UV 300 spectrometer was used. Rheological investigations were done at a

rotation-rheometer Rheostress 100 (Haake, DG 41 (double slit) at 25°C, shear gradient

0.5 to 40 s-1); zero shear viscosities could be obtained by creep-measurements (shear

stress 0.5 Pa).

For the continuous wet coating an in-house R2R laboratory coating machine LBA-200

was used as described in a former publication[36]. Also the R2R-produced PEDOT:PSS

layers were prepared like explained there. The slot die coating is variable in die lip gap

and die lip to substrate gap as well as caster arrangement/ angle and can be understood

as a combination of extrusion coating with bulge and with pulling, as known[45,57].

Spincoating was done on a semitec CPS20 machine in clean room (air). For

photovoltaic devices preparation in R2R mode the substrates were taken as roll-ware

without any cleaning procedures. Completions with top-electrodes were done for all

R2R-coated solar cells discontinuously in a glove box. Calcium and aluminum

(cathode) were thermally deposited (15 nm Ca, 50 nm Al) through a shadow mask in

vacuum (MB EVAP M. Braun), which defines a device area of 0.25 cm². J/V curves

were recorded with a Keithley SMU 2400 Source Meter by illuminating the cells from

the ITO side with 100 mW/cm² white light from a Steuernagel solar simulator to realize

AM1.5 conditions. A mono-crystalline silicon solar cell, calibrated at ISE Freiburg,

Germany was used as reference cell to confirm stabilization of 100 mW/cm²

illumination. All cells were prepared under ambient conditions (air) and annealed as

well as measured (because of the sensitive Ca) in inert atmosphere (Ar).

3. Results and discussion

3.1 P3HT:PCBM: R2R-coating and variation in solvents

6

Alternative literature known solvent variants with reduced halogen-content for solar cell

preparation are described for chloroform with ethyl alcohol[58], toluene with

chloroform[59], p-xylene[60,61], o-xylene[62], tetralin[63,64] or o-dichlorobenzene with

mesitylene[64]. In these cases remarkable efficiencies up to around 4 % could be

observed for devices coated on glass. In this sense not only the mentioned simple

replacement of solvents was aimed but also certain effects like pre-aggregation (fibers)

or low-/high-boiling combination (slow drying) to influence morphology. R2R-

application of non-halogenated system on ITO-PET had been described with 0.7 %

efficiency (module with 3 solar cells á 1 x 7 cm²) as well.[55] Film forming and also film

drying are not trivial and depend on the respective material (material combination). A

lot of different parameters (surface energies, temperatures, etc.) should be well matched

to stay in the coating window and to obtain a high quality dry film.[65]

For own R2R-coating o-xylene (Xy) was tested in comparison to chlorobenzene (CB)

and o-dichlorobenzene (DCB), that are known for best solubility and film-forming

ability in spin-coating process. The question was, whether DCB can be taken in R2R-

wet-coating process and what are the characteristics of PSCs manufactured out of it

versus R2R-proofed CB. And as second issue, can halogen-free solvent work as well as

CB? For this, the “old” standard system consisting of poly(3-hexylthiophene) (P3HT)

and phenyl-C60-butyric acid methyl ester (PCBM) was solved in ratio 1:0.8 (wt./wt.)

and 1.2 wt.% in each of the solvents. Xy was chosen because of good solving-character

for a non-halogenated solvent in combination with moderate boiling temperature ( bp =

144 °C) - higher than toluene and chloroform to give the film the time it needs for right

phase-separation, but low enough to dry at air in relatively short terms. The latter is very

important in technological considerations, especially for the engaged machinery. After

the caster-application the sensitive wet-foil is transported relatively straight and

horizontal into the dryer region and up to the moment the film is touch-dry mechanical

7

stress from web guide rolls should be strictly avoided, elsewhere inhomogeneities

occur. Anyway, the setup of the LBA200 requires a relatively fast film drying caused by

only 3 m horizontal drying zone. In principle this is no problem for very thin wet-

thicknesses of around 5-10 µm and also for other coatings that have the opportunity for

solidification by cross-linking due to UV-radiation or heat input by IR-radiation.

All the different solvent based inks of the here described coating were applied by slot

die caster with same dosage giving nominal 9 µm wet and around 100 nm dry film

thicknesses. Coating width was 5 cm and the coatings itself showed good wetting on the

R2R-coated PEDOT:PSS-ITO-foil. The wet film quality directly after application was

good in all cases. For hole-injection as well as photoactive layer formation out from Xy

see Figure 2 as sample.

To avoid fast degradation at air, the films were only allowed to dry at ambient

temperatures, except DCB with a boiling point of 180 °C, what was also tested in one

trial to dry with the help of an additional IR-heater (200 W).

The resulting films looked different (Fig. 3) both in color and in quality (homogeneity).

However the color depth is not that surprising. Considering that real densities of the

solvent differ extremely from the assumed 1 g/cm³ (Xy 0.86 g/cm³, CB 1.11 g/cm³,

DCB 1.30 g/cm³), the corresponding trend of layer thickness could be found by UV/Vis-

measurements: 93 nm Xy, 120 nm CB and 140 nm DCB (assumed 1 g/cm³ dry film

density). By tempering the samples in all the cases an increase of light absorption

appears as expected, too. But, as a result it can be noted that drying is the critical issue

in these coating variants. The high boiling point and the slow evaporation of DCB leads

to slower drying than hoped for and so still wet films reach the first roll for vertical web

transport, like explained above. DCB evaporates with an evaporation number E = 57

four times slower than CB (E = 12.5). With additional IR-drying before this point, the

film quality is better, but the temperatures at air led to accelerated degradation at air.

8

For overview of R2R-conditions and the manufactured solar cells out of it see Table 1 –

PSC 1-4. The appropriate J/V-curves to the summarized values are depicted in Figure

5. Best values could be obtained from CB (4). PSCs processed from DCB without IR-

drying (3) still give light power conversion efficiencies more than 1 %, but they are not

suitable for larger area/module-fabrication because of the poor surface quality. The

improved homogeneity of the surface with IR-radiation (2) is accompanied with a

counterproductive drop in the efficiency. The fill factor (FF) decreases indicating bad

morphology and/or degradation. However, remarkable 1.17 % for the Xy-variant (1)

could be recorded. The coating out of this solvent can bee seen as a real alternative for

photoactive-layer formation: good film quality and non-halogenated solvent production.

In ongoing research we will try thicker Xy-variants and better photoactive material

systems to improve the performance of this promising solvent.

In Figure 6 the surfaces resulting out of the different four experiments can be

compared. It can obviously be seen, that the roughness differs extremely. Both, a too

smooth (DCB+IR, 2) and also a too rough surface (DCB 3) – also standing for degree of

phase-separation (too less of nano-phase separation or too large clusters minimizing

D/A-interface layer) of the blend components, that is tricky to regulate but extremely

crucial for functionality in solar cell – are not wished.[66-68,2] Surface roughness with

maximum peaks in the range of 20-40 µm (Xy and CB) seem to be the best solution.

The determined results in layer formation and solar cell efficiencies are valid for the

special kind of machinery and technology-type. By using other coating machines, that

differ in construction (scales, web guide, drying, inert atmosphere), also a changed

ranking is possible. The investigation done can serve as help for their construction.

9

3.2 A “new” system: P3HT and bisindene-C60 - R2R-coating

To come closer the high values and performances of PSC, produced in lab-scale under

best conditions as reported in the last two years, the “new” system: P3HT and

bisindene-C60, known for their ability to manage more than 6 % on ITO-glass[9], was

chosen for testing suitability R2R-slot die technique for future production.

At the beginning solar cells on rigid substrates were prepared for proofing optimum

capacity of the donator-acceptor system. For this commercial inks from Plextronics®

were applied. The certain hole-injection layer (from Plextronics: Plexcore PV2000 hole

transport ink) was found by differential scanning calorimetry to be annealed at least at

150 °C to make sure to reach a phase-change at around 140 °C. The layers were

prepared in clean room at air, tempering was done in inert atmosphere (glove box) as

well as vapor deposition of the electrodes and measuring the characteristics of the PSC

under illumination (AM1.5). The best conditions were identified and listed in Table 1

yielding in 5.45 % (5) efficiency. The high open circuit voltage (Voc) is due to the

higher LUMO energy level of the bisindene-C60 in comparison to the standard-PCBM.

Calcium intermediate layer between photo-absorbing layer and aluminum top-electrode

is obligatory. The theory behind is still not clear, but we noticed without Ca for similar

devices less than 2 % efficiency. Annealing before thermal Ca/Al-deposition in vacuum

at 170 °C for 15 min was also done inert.

To achieve R2R-coating at first the commonly used and well-proofed Clevios system

was tried to replace the not exactly specified commercial PV2000 hole transport ink.

With this even higher short current density (Jsc) could be measured (6). The second step

was a transition from rigid glass-substrates to flexible ITO-foils, so that the complete

Plextronics system (hole-injection and photoactive layer) was checked in comparison to

hole-injection layer out of Clevios PH with Plexcore PV2000 photoactive ink. It is

important to exchange Clevios 4083 with Clevios PH because of the less acid character

10

and the better compatibilization with the more sensitive ITO on foil. In addition

annealing tests were done to optimize. The PSC were annealed before deposition of the

Ca/Al-electrodes. Like recommended by Plextronics for PSC on glass, the high

temperature of 170 °C is also required on foil to give best performances (Fig. 7). Higher

temperatures were not tested with respect to the thermal stability of the PET.

In both cases for PSC 8 and 9 nearly the same parameters were found, giving 4.5 %

light power conversion efficiency (η). Because of the reduced surface resistance of ITO

on foil vs. glass the Jsc becomes smaller, but still proper values for flexible devices.

The third point was defining the composition of the photoactive material to exchange

the commercial PV 2000 photoactive ink, based on DCB as solvent. From the

experiments explained above (s. 3.1) the R2R-wet-coating at LBA-200 incompatible

pure DCB must be excluded. For ratio finding also for comparison with best values

applied on glass experiments were done on glass still from DCB. With the in-house

developed ink P3HT:bisindene-C60 1:0.8 nearly 5 % efficiency could be achieved (7).

Now we had a system, ready to use in larger coating-scale with on hand material stock

gram-scale to be transferred in applicable formulation (solvent system).

To make sure about wetting the reel-ware ITO-foil and later the PEDOT:PSS-coated

ITO-foil was checked be measuring contact angels before R2R-coating. The surface

energy of the untreated ITO-PET was 32.5 mN/m (dispersive 29.5 mN/m; polar 3.0

mN/m), freshly treated with corona (air) R2R (2 m/min) 49.9 (28.5; 21.4) mN/m. The

PEDOT:PSS (R2R 2 m/min) surface is also in this range with 51.4 (30.6; 20.8) mN/m

and makes sure that photoactive ink will give good wetting. The wetting envelopes of

the foils show that for instance isopropyl alcohol (IPA) addition to the PEDOT:PSS

causes a shift (71.7 mN/m to 21.9 mN/m) in the pretreated enhanced coating window of

the ITO-foil (Fig. 8). Viscosities and relation to shear stress of the PEDOT-PSS

derivatives were measured, too. The zero shear viscosity of PH is 64.0 mPas (50.8 mPas

11

at 40 s-1) and PH:IPA 1:1 39.0 mPas (33.1 mPas at 40.5 s-1); the viscosity is nearly

independent on shear stress while 4083 showed Newton-fluid behavior below 5 mPas.

With these preliminary investigations the R2R-coating trials started. However the first

results with pristine CHCl3 and CB were not fruitful. The film quality as well as the

efficiency of PSC were not good. Inspired by R2R-coating results for PCBM-systems

Krebs et al. describe[35] by taking mixtures consisting out of CHCl3 and DCB we tried

to transfer this on our system. In all mixtures with CHCl3:DCB the wetting was really

good, like expected from 3.1. The difficulties are to reach solidification (removing the

residual solvent) of the wet coated layer before mechanical stress from web transport let

the wet film drift. But also too fast drying is not wished, because of better film-

morphology with slower drying[69].

Experiments with small coating width (1.5 cm), applying CHCl3:DCB 1:2 in 4 wt.%

followed by manufacturing of PSC from samples out of it, show in principal good solar

cells with η larger 2 %. But the coating process is not stable enough. The concentration

is too high to stay continuously into the coating window to reach around 200 nm

thickness in dry layer. With the used concentration the coating tends to result in thicker

layers. Also the DCB content is still too high to avoid drifting of the wet film

completely. The value given in Table 1 (10) stands for only a few pieces. Much better

results were yielded with reduced concentration to 3 wt.% and 1:1 mixture of the

solvents. The surface energy of this ink was 25.3 mN/m (dispersive 20.5 mN/m; polar

4.8 mN/m) and lies within the wetting envelope of the PEDOT:PSS coated surface

excellently (Fig. 8). Using this ink for slot-die coating the obtained photoactive layer

was continuously homogeneous and touch-dry in time. The characteristic parameters of

the performance from PSC (Table 1, 11 and 12) out of these reels are representative for

the entire coating. Indeed η = 3.2 % is the best obtained value, but nearly all solar cells

12

manufactured from coated area of several meters give 2.5 up to more than 3 % light

power conversion efficiency. Up-scaling to 8 cm coating width was reached in PSC

(reel) 11 (sample s. Fig. 9). The layer thickness of 260 nm was a bit too high; the

performance of the thinner one (12) is better. The surface is with maximum peaks at 40

nm relatively rough (Fig. 10), but in the optimum-region (for R2R on foil) found for

P3HT:PCBM for other solvents (3.1).

To summarize, in Figure 11 the J/V-curves of the best fabricated PSC from each field:

SC (spin-coating) on glass (6), SC on foil (9) and R2R on foil (12) are depicted. As can

be clearly seen, the fill factor of the R2R-PSC is still too small in comparison to the SC-

PSC on foil. Smoother surfaces with inner well-done phase-separation and/or other

kinds of morphology influencing effect (additives, other solvent mixtures) can help to

increase FF and with that, we think the correlated Jsc will increase too.

By connecting manually separated cells out of R2R-coated stripes PSC modules with

nine single solar cells could be manufactured. For those it was not the aim of the work

to improve lifeterm-stability. The modules were not especially protected against

degradation influences, only demonstrate feasibility of introduction in a new kind of

device (design) and a short phase of function. Sure, high-barrier foils are necessary to

avoid degradation[70,71] at least to guarantee lifetimes of two years.

Like Neuber´s solar energy bag[72] and the solar hat

[73] textile integration is an ideal

niche for PSC. In Figure 12 a jacket for children as prototype is depicted, that can serve

as a good entrance to larger volume application as well. The heatable pockets and the

luminescent stripes (incorporated conductive threads [74]), which can warm children

hands in the cold and make them actively visible in the dark, increase safety and

comfort while wearing such clothes. Open pockets for the solar modules were designed,

that they can easily be taken out for jacket washing. At day (in sun/light) the six affixed

13

solar cell modules can load the incorporated accumulator, powering the installed electric

functionalities.

But, neither investigation for finding best kind for connecting single PSC to modules

nor wearing tests of the textile were done. The showing of the special setup and its

visualization (marketing) was the aim. Nevertheless we see huge potential in laser-

ablation as patterning technique, what can also be done in R2R modus, and have gained

positive experiences in polymer field effect transistors production what now is going to

be transferred onto PSCs. [75]

“… cautious in predicting …” and without “… overhyping the technology …”, He and

Yu appropriate pointed out[76], the jacket as prototype shows an alternative PSC-product

niche, indeed with enlarging potential. Next to the look and the energy supply of the

PSCs the additional new functionalities in textiles are the main important features as

arguments for costumers not only children to acquire such products. With the growing

field of smart textiles polymer photovoltaics will have good chances to go alongside.

4. Conclusion

Starting with investigations and comparison of R2R-coating of standard system

P3HT:PCBM with different solvents it is to note that even the non-halogenated o-xy-

lene can be suitable for future large-scale application, showing good layer formation

and respectable efficiency of PSC prepared out of it. Pristine DCB cannot be applied at

the special used coating machine; the slow wetting complicates the drying. These results

were transferred onto the “new” photoactive system P3HT and bisindene-C60. On ITO-

PET 4.55 % light power conversion efficiency can be achieved with spin-coating and

14

even R2R production with 8 cm coating width and 1 m/min at air makes 3.2 % possible.

With these, in our opinion, good values for flexible and for R2R-produced PSCs

industrial applications move closer.

Manufactured PSC-modules could be introduced in a special functional jacket for

children open an alternative product niche. The safety benefit by wearing such textiles

goes beyond a simple outdoor recreational application.

Acknowledgements

Financial support of this work by the Thuringian Ministry (TMWAI 2004 WI0282), by

the BMBF (03X3518A “sonntex”) and by the BMWI (IW061016; 1136/03, VF071005,

IW082026, VF090063 and KA0406302DA7) is gratefully acknowledged. We wish to

thank Frank Apsel and his team from Maba GmbH Wolfen for technological support at

the LBA-200. Our special thanks go to Klaus Richter for the fruitful work regarding

jacket development.

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24

Figure 1: Schematic illustration of R2R-coating

Figure 2: Slot die coating of P3HT:PCBM from o-xylene: 1 m/min, 5 cm (1)

Figure 3: R2R-coated PET-ITO-reels and sample stripes: left to right – PEDOT:PSS (Clevios PH) and 3, 2, 4, 1 and 1 trimmed width

Figure 4: UV/Vis transmission curves of R2R-made PSC 1-4 (Table 1, without top-electrodes) in relation to the pristine ITO-foil and coated with hole-injection layer (Clevios PH); inset: UV/Vis transmission curves before and after 5 min 100 °C (inert) Figure 5: J/V characteristics of best flexible solar cells PET/ITO/PEDOT:PSS(2 m/min R2R)/P3HT:PCBM(1 m/min R2R)/Al out of Table 1: blue rhombs - 4, green dotted - 1, red triangles - 3 and dark red squares - 2 Figure 6: AFM topography (left) and phase (right) of R2R-coated P3HT:PCBM on R2R-coated PEDOT:PSS layer (1-4 from Table 1, 10 x 10 µm²) Figure 7: Averaged conversion efficiencies (ηav) of spin-coated PSCs on foil depending on the annealing temperature: black rhombs – prepared similar to 8 (Tab. 1); red

squares - prepared similar to 8 (Tab. 1) with thinner photoactive layer (440 rpm instead of 400 rpm) Figure 8: Surface energy wetting envelopes (activation by corona: R2R 1 m/min, air; IPA = isopropyl alcohol; photoactive formulation = chloroform/1,2-dichlorobenzene 1/1 3 wt.% P3HT/bisindene-C60 1/1) Figure 9: Sample of 11 (Table 1), cutting for subsequent PSC and module manufacturing

Figure 10: AFM topography (left) and 3D-topography (right) for visualization of R2R-coated P3HT:bisindene-C60 surfaces on R2R-coated PEDOT:PSS- ITO-layer (10 x 10 µm², 11) Figure 11: J/V characteristics of best flexible solar cells PET/ITO/PEDOT:PSS/

P3HT:bisindene-C60/Ca/Al out of Table 1: red dotted – photoactive layer - 400 rpm/5 min spin-coating (9); blue squares - PEDOT:PSS -R2R (2 m/min) and photoactive layer R2R ( 1m/min) (12) in comparison to similar setup on ITO-glass (black rhombs, 6) Figure 12: left above: PSC-module, fabricated out of R2R-coated samples, separated by laser ablation (KrF-excimer 248 nm) and connected by Al-evaporation and textile integration (by Richter+Partner, Weimar) - right and left below – PSC as energy provider for LED-stripes and warming pockets in a jacket for children Table 1: Summary of experimental parameters for PSCs: different coating methods and variation in materials/compositions

25

Figure 1: Schematic illustration of R2R-coating

TCO-foil (ITO)

hole injection layer

photoactive layer

„reel–to–reel (R2R)“

slot-die-coatingn

S

(CH2)5CH3

+

26

Figure 2: Slot die coating of P3HT:PCBM from o-xylene: 1 m/min, 5 cm (1)

27

Figure 3: R2R-coated PET-ITO-reels and sample stripes: left to right – PEDOT:PSS (Clevios PH) and 3, 2, 4, 1 and 1 trimmed width

28

Figure 4: UV/Vis transmission curves of R2R-made PSC 1-4 (Table 1, without top-electrodes) in relation to the pristine ITO-foil and coated with hole-injection layer (Clevios PH); inset: UV/Vis transmission curves before and after 5 min 100 °C (inert)

0

20

40

60

80

100

200 300 400 500 600 700 800 900 1000

wavelength [nm]

tra

nsm

issi

on

[%

]

CBDCB + IRDCBXyPET-ITO PET-ITO-PH

30

40

50

60

70

400 450 500 550 600 650

wavelength [nm]

tra

nsm

issi

on

[%

]

CB temperedDCB temperedXy temperedCBXyDCB

increasing

absorption

29

Figure 5: J/V characteristics of best flexible solar cells PET/ITO/PEDOT:PSS(2 m/min R2R)/P3HT:PCBM(1 m/min R2R)/Al out of Table 1: blue rhombs - 4, green dotted - 1, red triangles - 3 and dark red squares - 2

-30

0

30

60

90

120

150

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

voltage [V]

curr

ent

den

sity

[m

A/c

m2]

-6

-5

-4

-3

-2

-1

0

1

2

3

4

0.0 0.1 0.2 0.3 0.4 0.5 0.6

voltage [V]

curr

ent

den

sity

[m

A/c

m2]

chlorobenzene

xylene

1,2-dichlorobenzene without IR

1,2-dichlorobenzene with IR

30

CB

Xy

DCB without IR drying

DCB with IR drying

Figure 6: AFM topography (left) and phase (right) of R2R-coated P3HT:PCBM on R2R-coated PEDOT:PSS layer (1-4 from Table 1, 10 x 10 µm²)

31

Figure 7: Averaged conversion efficiencies (ηav) of spin-coated PSC on foil depending on the annealing temperature: black rhombs – prepared similar to 8 (Tab. 1); red

squares - prepared similar to 8 (Tab. 1) with thinner photoactive layer (440 rpm instead of 400 rpm)

3.9

4.0

4.1

4.2

4.3

4.4

4.5

145 150 155 160 165 170 175

annealing temperature [°C]

ηη ηηa

v [

%]

400 rpm

440 rpm

32

Figure 8: Surface energy wetting envelopes (activation by corona: R2R 1 m/min, air; IPA = isopropyl alcohol; photoactive formulation = chloroform/1,2-dichlorobenzene 1/1 3 wt.% P3HT/bisindene-C60 1/1)

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60

dispersive part [mN/m]

pola

r p

art

[m

N/m

]

ITO

ITO + 200 W corona

ITO coated with Clevios PH

corona treatmentClevios PHClevios PH:IPA 1:1

photoactive formulation

33

Figure 9: Sample of 11 (Table 1), cutting for subsequent PSC and module manufacturing

34

Figure 10: AFM topography (left) and 3D-topography (right) for visualization of R2R-coated P3HT:bisindene-C60 surface on R2R-coated PEDOT:PSS- ITO-layer (10 x 10 µm², 11)

35

Figure 11: J/V characteristics of best flexible solar cells PET/ITO/PEDOT:PSS/

P3HT:bisindene-C60/Ca/Al out of Table 1: red dotted – photoactive layer - 400 rpm/5 min spin-coating (9); blue squares - PEDOT:PSS -R2R (2 m/min) and photoactive layer R2R (1m/min) (12) in comparison to similar setup on ITO-glass (black rhombs, 6)

-11.0

-8.5

-6.0

-3.5

-1.0

1.5

4.0

6.5

9.0

0 0.2 0.4 0.6 0.8

voltage [V]

curr

ent

den

sity

[m

A/c

m2]

spincoating glass

spincoating foil

R2R-coating foil

36

Figure 12: left above: PSC-module, fabricated out of R2R-coated samples, separated by laser ablation (KrF-excimer 248 nm) and connected by Al-evaporation and textile integration (by Richter+Partner GmbH; Weimar) - right and left below – PSC as energy provider for LED-stripes and warming pockets in a jacket for children

LED-stripe

heatable pocket

PSC-modules

37

Table 1: Summary of experimental parameters for PSCs: different coating methods and variation in materials/compositions PSC ITO hole-injection layer photoactive layer ηηηηmax

f)

on mat.a)

coat.b)

drying mat.c)

solvent d)

coat. b)

drying Td

e)

[nm] (Voc;Jsc;FF)

1 foil Clevios PH:IPA

R2R 2 m/min,

5 cm

R2R 7 min 90 °C

P3HT: PCBM 1:0.8

1.2 wt.% Xy

R2R 1 m/min,

5 cm

R2R RT

108 1.17 %

(587; 3.94; 0.50)

2 foil Clevios PH:IPA

R2R 2 m/min,

5 cm

R2R 7 min 90 °C

P3HT: PCBM 1:0.8

1.2 wt.% DCB

R2R 1 m/min,

5 cm

R2R + 200 W

IR 108

1.02 %

(561; 5.13; 0.35)

3 foil Clevios PH:IPA

R2R 2 m/min,

5 cm

R2R 7 min 90 °C

P3HT: PCBM 1:0.8

1.2 wt.% DCB

R2R 1 m/min,

5 cm

R2R RT

108 1.26 %

(526; 4.74; 0.51)

4 foil Clevios PH:IPA

R2R 2 m/min,

5 cm

R2R 7 min 90 °C

P3HT: PCBM 1:0.8

1.2 wt.% CB

R2R 1 m/min,

5 cm

R2R RT

108 1.37 %

(601; 4.81; 0.47)

5 glass hole

transport inkg)

SC 1000 rpm

30 min 150 °C

air

PV 2000g)

2.0 wt.% DCB

SC 400 rpm 4.5 min

RT - 5.45 %

(831; 9.75; 0.67)

6 glass Clevios

4083

SC 1200 rpm

5 min 150 °C

air

PV 2000g)

2.0 wt.% DCB

SC 400 rpm

6 min RT -

5.80 % (823; 10.3; 0.68)

7 glass Clevios

4083

SC 1200 rpm

5 min 150 °C

air

P3HT: BIC60 1:0.8

1.8 wt.% DCB

SC 400 rpm

6 min RT -

4.93 %

(832; 9.26; 0.64)

8 foil hole

transport inkg)

SC 1000 rpm

15 min 150 °C

air

PV 2000g)

2.0 wt.% DCB

SC 400 rpm

6 min RT -

4.55 %

(836; 8.37; 0.65)

9 foil Clevios PH:IPA

SC 1200 rpm

10 min 120 °C

air

PV 2000g)

2.0 wt.% DCB

SC 400 rpm

6 min RT -

4.55 % (804; 8.56; 0.66)

10 foil Clevios PH:IPA

R2R 2 m/min,

4 cm

R2R 7 min 90 °C

P3HT: BIC60 1:0.8

4 wt.% DCB: CHCl3

2:1

R2R 1 m/min, 1.5 cm

R2R RT

187 2.82 %

(805; 6.47; 0.54)

11 foil Clevios PH:IPA

R2R 2 m/min,

7 cm

R2R 7 min 90 °C

P3HT: BIC60 1:0.8

3 wt.% DCB: CHCl3

1:1

R2R 1 m/min,

8 cm

R2R RT

206 (260)

2.71 % (796; 6,59; 0.52)

12 foil Clevios PH:IPA

R2R 2 m/min,

4 cm

R2R 7 min 90 °C

P3HT: BIC60 1:0.8

3 wt.% DCB: CHCl3

1:1

R2R 1 m/min,

5 cm

R2R RT

180 (218)

3.20 %

(800; 7.31; 0.55)

a) material: type of PEDOT:PSS-dispersion, Clevios PH:IPA (isopropyl alcohol) 1:1 (R2R, found thickness of dried film by ellipsometry ≈ 80-100 nm), 7:1 (SC, found thickness of dried film by ellipsometry ≈ 100 nm); b) kind of coating at air: R2R = reel-to-reel at LBA200, SC = spincoating in clean room with velocities and width; c) material: type and ratio of polymeric electron donator to fullerene-acceptor; d) concentration of photoactive material in solvent: Xy = o-xylene, DCB = o-dichlorobenzene, CB = chlorobenzene, DCB:CHCl3; 1:1 e) calculated thicknesses of dried R2R-made layers (Td), for calculation was used: Td = Q • c • ρliquid/(w • v • ρsolid • 100) assuming ρliquid = ρsolid = 1 g/cm³, Q = flow rate (ml/min), v = velocity (m/min), in brackets found by ellipsometry; f) best solar cell (Voc in mV, Jsc in mA/cm²), AM1.5, A = 0.25 cm², completion of cells on foil with PCBM (1-4) by evaporation of Al electrode and following annealing 5 min/100°C, completion of 5-12 by annealing 15 min/170°C and following evaporation of Ca (15 nm) and Al (50 nm), g) commercial product by Plextronics: Plexcore PV2000 hole transport ink and Plexcore PV2000 photoactive ink