Thomas Rieks Andersen

Scalable, ambient atmosphere roll-to-roll manufacture of encapsulated large area, flexible organic tandem solar cell modules

Inline printing and coating methods have been demonstrated to enable a high technical yield of fully roll-to-roll processed polymer tandem solar cell modules. We demonstrate generality by employing different material sets and also describe how the ink systems must be carefully co-developed in order to reach the ambitious objective of a fully printed and coated 14-layer flexible tandem solar cell stack. The roll-to-roll methodologies involved are flexographic printing, rotary screen printing, slot-die coating, X-ray scattering, electrical testing and UV-lamination. Their combination enables the manufacture of completely functional devices in exceptionally high yields. Critical to the ink and process development is a carefully chosen technology transfer to industry method where first a roll coater is employed enabling contactless stack build up, followed by a small roll-to-roll coater fitted to an X-ray machine enabling in situ studies of wet ink deposition and drying mechanisms, ultimately elucidating how a robust inline processed recombination layer is key to a high technical yield. Finally, the transfer to full roll-to-roll processing is demonstrated.

Roll-Coated Fabrication of Fullerene-Free Organic Solar Cells with Improved Stability

Large area, fullerene‐free organic solar cells with improved stability and efficiency of up to 1% are fabricated by the roll‐coating process on indium tin oxide free and flexible substrates, under ambient conditions.

Roll-coating fabrication of flexible large area small molecule solar cells with power conversion efficiency exceeding 1%

All solution-processed flexible large area small molecule bulk heterojunction solar cells were fabricated via roll-coating technology. Our devices were produced from slot-die coating on a lab-scale mini roll-coater under ambient conditions without the use of spin-coating or vacuum evaporation methods. Four diketopyrrolopyrrole based small molecules (SMs 1–4) were utilized as electron donors with (6,6)-phenyl-C61-butyric acid methyl ester as an acceptor and their photovoltaic performances based on roll-coated devices were investigated. The best power conversion efficiency (PCE) of 1.01%, combined with an open circuit voltage of 0.73 V, a short-circuit current density of 3.13 mA cm−2 and a fill factor of 44% were obtained for the device with SM1, which was the first example reported for efficient roll-coating fabrication of flexible large area small molecule solar cells with PCE exceeding 1%. In addition, roll-coated devices based on SMs 2–4 also showed good performances with PCEs of 0.41%, 0.54%, and 0.31%, respectively. Our results prove that small molecules have the potential for use in industries for large scale production of efficient organic solar cells.

The influence of additives on the morphology and stability of roll-to-roll processed polymer solar cells studied through ex situ and in situ X-ray scattering

The effect of twelve different additives on organic solar cells with an active layer based on poly-3-hexylthiophene (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) has been studied in this work and tested for suitability in roll-to-roll slot-die coating. Three of the twelve additives increased the solar cell efficiency while the rest showed no effect or a negative influence on the efficiency and coatability. In cases where the additive caused an increase in performance the relation to surface topography and the structure was investigated using Atomic Force Microscopy (AFM), UV-Vis Spectroscopy and Small Angle X-ray Scattering (SAXS) for cells prepared with 1-chloronaphthalene (CN), N-methyl-2-pyrrolidone (NMP) and 1,3-dimethyl-barbituric acid (BARB) as processing additives. The studies suggested that the use of these additives resulted in films with improved morphology and electrical properties of the active layer. The effect of the CN on structural evolution during different solvent evaporation and annealing times was further investigated with an in situ roll-to-roll X-ray study. Lifetime studies under continuous illumination were used to assess the impact of the additives on the stability of the prepared devices that had an active area of 1 cm2.

Comparison of additive amount used in spin-coated and roll-coated organic solar cells

All-polymer and polymer/fullerene inverted solar cells were fabricated by spin-coating and roll-coating processes. The spin-coated small-area (0.04 cm2) devices were fabricated on indium tin oxide (ITO) coated glass substrates in nitrogen. The roll-coated large-area (1.0 cm2) devices were prepared on ITO-free flexible substrates under ambient conditions. The use of a solvent additive, 1,8-diiodooctane (DIO), facilitated phase separation and enhanced power conversion efficiencies (PCEs). The PCE of polymer/fullerene solar cells increased from 4.58% to 8.12% with 2.5% (v/v) DIO when using the spin-coating process, and increased from 1.37% to 2.09% with 5% (v/v) DIO in the roll-coating process. The PCE of all-polymer solar cells increased from 1.44% to 3.51% with 4% (v/v) DIO when employing the spin-coating process. For the roll-coated large area devices the PCE increased from 0.15% to 0.73% with 9% (v/v) DIO. The optimal amounts of DIO, when using the roll-coating process for the two different active layers (5% and 9% respectively) are significantly higher than those for the spin-coating process (2.5% and 4%, respectively), which is ascribed to a fundamentally different drying mechanism.

Flexible ITO-free organic solar cells applying aqueous solution-processed V2O5 hole transport layer: An outdoor stability study

Solution processable semiconductor oxides have opened a new paradigm for the enhancement of the lifetime of thin film solar cells. Their fabrication by low-cost and environmentally friendly solution-processable methods makes them ideal barrier (hole and electron) transport layers. In this work, we fabricate flexible ITO-free organic solar cells (OPV) by printing methods applying an aqueous solution-processed V2O5 as the hole transport layer (HTL) and compared them to devices applying PEDOT:PSS. The transparent conducting electrode was PET/Ag/PEDOT/ZnO, and the OPV configuration was PET/Ag/PEDOT/ZnO/P3HT:PC60BM/HTL/Ag. Outdoor stability analyses carried out for more than 900 h revealed higher stability for devices fabricated with the aqueous solution-processed V2O5.

Structure and crystallinity of water dispersible photoactive nanoparticles for organic solar cells

Water based inks would be a strong advantage for large scale production of organic photovoltaic devices. Formation of water dispersible nanoparticles produced by the Landfester method is a promising route to achieve such inks. We provide new insights into the key ink properties of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanoparticles such as the internal structure and crystallinity of the dispersed nanoparticles and the previously unreported drastic changes that occur when the inks are cast into a film. We observe through transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) that the nanoparticles in dispersion are spherical with the nanodomains of P3HT being partly crystalline. When wet processed and dried into films, the nanoparticles lose their spherical shape and become flattened into oblate shapes with a large aspect ratio. Most particles are observed to have a diameter 13 times of the particle height. After casting into a film, the crystal domains adopt a preferred orientation with the majority of the nanocrystals (68%) with face-on orientation to the substrate. We propose that low substrate surface energy is responsible for particle deformation and texturing.

An isoindigo containing donor-acceptor polymer: synthesis and photovoltaic properties of all-solution-processed ITO- and vacuum-free large area roll-coated single junction and tandem solar cells

In this work, the design, synthesis, and characterization of a donor–acceptor polymer from dithieno[3,2-b:2′,3′-d]pyrrole and isoindigo (i-ID) are presented. The synthesized polymer has been applied in the fabrication of large area ITO-free organic photovoltaic devices, both by spin coating and roll coating; the latter was used to construct both single junction and multi-junction organic photovoltaic (OPV) architectures.

Roll-coating fabrication of ITO-free flexible solar cells based on a non-fullerene small molecule acceptor

We report organic solar cells (OSCs) with non-fullerene small molecule acceptors (SMAs) prepared in large area via a roll coating process. We employ all solution-processed indium tin oxide (ITO)-free flexible substrates for inverted solar cells with a new SMA of F(DPP)2B2. By utilizing poly(3-hexylthiophene) as donor blended with F(DPP)2B2 as acceptor, ITO-free large-area flexible SMA based OSCs were produced under ambient conditions with the use of slot-die coating and flexographic printing methods on a lab-scale compact roll-coater that is readily transferrable to roll-to-roll processing. The effect of different processing solvents on the device performance was investigated, and the best performance with a power conversion efficiency of 0.65%, an open circuit voltage of 0.85 V, a short-circuit current density of 2.19 mA cm−2, and a fill factor of 35% was obtained.

Medium area, flexible single and tandem junction solar cells based on roll coated semi-random copolymers

We report on medium area (1 cm2) slot-die coated organic photovoltaic devices (OPVs) of a recently developed semi-random copolymer of poly-3-hexylthiophene and diketopyrrolopyrrole (P3HTT–DPP-10%) mixed with phenyl-C61-butyric acid methyl ester ([60]PCBM). The devices were prepared using a compact laboratory roll-coater using only slot-die coating and flexographic printing under ambient conditions on a flexible ITO-free substrate. In order to overcome a low JSC and FF obtained for single junction devices, devices were also prepared in a tandem geometry making it possible to employ thinner junction films. Power conversion efficiencies of up to 1.36% and 1.31% were achieved for the tandem and single junction geometries, respectively.