Sustainability and circular economy cover the principles of designing out waste and pollution, keeping products and materials in use, and regenerating natural systems. Due to global trends (eg. increasing e‐waste and material consumption) and global sustainability goals also electronics industry has to consider how to increase sustainability in its products, operations and service models. VTT has demonstrated sustainable electronic solutions by developing bio‐based and renewable material processing, by utilizing high‐speed printing and hybrid integration manufacturing processes, and by evaluating environmental impact of electronic systems and devices. This paper covers the different aspects of sustainability and highlights solutions demonstrated at VTT.

The funding note is missing in the paper. The funding note to add is the following: Open access funding provided by Technical Research Centre of Finland (VTT).

Indene‐C60‐bisadduct (ICBA) can represent an excellent choice as an acceptor of organic solar cells due to the, at most, similar cost, higher efficiency, and higher open‐circuit voltage (VOC) obtained in small‐scale devices compared to phenyl[60]butyrate methyl ester ([60]PCBM). We have investigated ICBA in printed solar cells and assessed the upscale of the printing process to a roll‐to‐roll (R2R) pilot production. Performances of poly(3‐hexylthiophene):ICBA solar cells are confirmed to be superior compared to [60]PCBM. Using large scale 2D R2R printing techniques, with both active material systems excellent processability, reproducibility, and yield are reached. At first, ICBA based large area modules (57 cm2) showed significant loss in efficiency. However, stressing the devices by exposure to sunlight was found to lead high efficiency modules with a VOC of 0.78 V per cell and a PCE of 3.4%. This is among the highest VOC per cell values realized with fully R2R processed organic photovoltaic modules and among the highest PCEs with P3HT based R2R processed modules. Imaging techniques have allowed to identify that stressing with sunlight partially burns shunts and recovers S‐shaped behavior in the ICBA‐based modules.

Understanding the phenomena at interfaces is crucial for producing efficient and stable flexible organic solar cell modules. Minimized energy barriers enable efficient charge transfer, and good adhesion allows mechanical and environmental stability and thus increased lifetime. We utilize here the inverted organic solar module stack and standard photoactive materials (a blend of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester) to study the interfaces in a pilot scale large-area roll-to-roll (R2R) process. The results show that the adhesion and work function of the zinc oxide nanoparticle based electron transport layer can be controlled in the R2R process, which allows optimization of performance and lifetime. Plasma treatment of zinc oxide (ZnO) nanoparticles and encapsulation-induced oxygen trapping will increase the absolute value of the ZnO work function, resulting in energy barriers and an S-shaped IV curve. However, light soaking will decrease the zinc oxide work function close to the original value and the S-shape can be recovered, leading to power conversion efficiencies above 3%. We present also an electrical simulation, which supports the results. Finally, we study the effect of plasma treatment in more detail and show that we can effectively remove the organic ligands around the ZnO nanoparticles from the printed layer in a R2R process, resulting in increased adhesion. This postprinting plasma treatment increases the lifetime of the R2R printed modules significantly with modules retaining 80% of their efficiency for ∼3000 h in accelerated conditions. Without plasma treatment, this efficiency level is reached in less than 1000 h.

A novel high‐durability multifunctional organic–inorganic hybrid coating material is presented in this work as luminescent down‐shifting (LDS) host matrix system for flexible organic photovoltaic (OPV) devices. Such new LDS coating is obtained by incorporating a convenient fluorescent organic dye in an appropriately functionalized fluoropolymeric resin that can be readily crosslinked by means of a dual‐cure mechanism with a single‐step ambient‐temperature photo‐induced sol–gel process. Due to its peculiar characteristics, the newly proposed system may be readily implemented in heat‐sensitive flexible devices. By carefully tuning the amount of organic fluorophore in the hybrid coating material, a maximum increase in power conversion efficiency exceeding 4% is achieved on devices incorporating the new LDS layer with respect to control systems. This represents the highest efficiency enhancement reported to date on flexible OPVs by means of a polymer‐based LDS layer. In addition, long‐term accelerated weathering tests (>550 h) highlight the excellent stability of LDS‐coated OPV devices, which can retain 80% of their initial performance, as opposed to the dramatic efficiency decay experienced by control uncoated devices. The approach presented here opens the way to the straightforward incorporation of versatile multifunctional light‐managing layers on flexible OPV systems for improved device efficiency and lifetime.

A roll-to-roll (R2R) calendering process was developed and used to improve the conductivity of rotary screen printed microparticle silver conductors. Two commercial microparticle silver pastes were used. In the calendering process, the rotary screen printed microparticle silver conductors are compressed under pressure and heat in order to make the porous microparticle layer denser and flatter. The results show that the resistivity of the rotary screen printed microparticle silver conductors was dramatically dropped after the R2R calendering process by 29-56 % depending on the silver paste. The complete drying of the calendered conductor layer decreased the resistivity even further as a result of which the layer resistivity was decreased 74 % from its initial value. The roughness of the silver conductors was also reduced remarkably after the calendering by 45-72 %. The effect of the R2R calendering process on the printed inductively remote readable capacitive moisture sensor based on simple inductor-conductor resonant circuit was also demonstrated. Calendering improved the Q-factor of the sensor but decreased the resonance frequency.

Keep it rolling! The cover image shows a portion of a solar cell roll on a 30 cm wide plastic substrate, patterned by gravure and rotary screen printing processes. The cells consist of an inverted structure, where the gravure-printed zinc oxide layer was exposed to a roll-to-roll plasma treatment to increase the adhesion and performance of the cells. The Full Paper by Marja Vilkman and colleagues at VTT Technical Research Centre of Finland and ENI S.p.A. on page 407 shows that the process can reach average solar cell performance of 2.9 % by using commercially available materials.

The solution-based deposition of the metal back electrode in inverted polymer solar cells (PSCs) using roll-to-roll (R2R) compatible processing technologies is considered one of the crucial issues towards the upscaling of PSC technology, as it may allow the full exploitation of the high through-put and prospective low-costs envisaged by the R2R fabrication approach. In this work, a water-based solution-processable silver ink formulation with low annealing temperature was developed to be used as precursor for the fabrication of the metallic back-electrode in flexible inverted PSC devices fabricated by means of R2R-compatible printing techniques. In order to investigate the effect of the deposition of such reactive silver ink on the underlying PSC layers, different back-electrode architectures were investigated and thoroughly characterized. In addition, the influence of the thickness of the hole-transporting poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer on the functional performance of the PSC devices was also investigated and an optimized combination of back-electrode architecture and PEDOT:PSS thickness was found, that also allowed to obtain semi-transparent PSC devices. The results of this study demonstrate the possibility to employ R2R-compatible processing techniques for the deposition of the metallic back-electrode in flexible inverted PSCs from a solution-processable water-based reactive silver ink formulation characterized by low-annealing temperature, and provide useful insights into the key role played by the hole-transporting buffer layer in the realization of fully functional flexible PSC devices.

We present a gravure printing process for zinc oxide (ZnO) nanoparticle ink to be used as a hole-blocking layer in inverted organic solar cells, enabling the production of patterned devices with freedom of design. The printability of the ink is optimized in a pilot-scale roll-to-roll (R2R) process, leading to smooth layers having a thickness of few tens of nanometers. The properties of the printed ZnO film are further optimized using R2R post-printing plasma treatment, which leads to increased adhesion and power conversion efficiency (PCE). The functionality of the printed ZnO layer is demonstrated in fully R2R-printed inverted solar cells showing high performance (2.9% mean PCE).

We describe the fabrication of roll-to-roll (R2R) printed organic photovoltaic (OPV) modules using gravure printing and rotary screen-printing processes. These two-dimensional printing techniques are differentiating factors from coated OPVs enabling the direct patterning of arbitrarily shaped and sized features into visual shapes and, increasing the freedom to connect the cells in modules. The inverted OPV structures comprise five layers that are either printed or patterned in an R2R printing process. We examined the rheological properties of the inks used and their relationship with the printability, the compatibility between the processed inks, and the morphology of the R2R-printed layers. We also evaluate the dimensional accuracy of the printed pattern, which is an important consideration in designing arbitrarily-shaped OPV structures. The photoactive layer and top electrode exhibited excellent cross-dimensional accuracy corresponding to the designed width. The transparent electron transport layer extended 300 µm beyond the designed values, whereas the hole transport layer shrank 100 µm. We also examined the repeatability of the R2R fabrication process when the active area of the module varied from 32.2 cm(2) to 96.5 cm(2). A thorough layer-by-layer optimization of the R2R printing processes resulted in realization of R2R-printed 96.5 cm(2) sized modules with a maximum power conversion efficiency of 2.1% (mean 1.8%) processed with high functionality.

Gravure printing as direct patterning roll-to-roll (R2R) production technology can revolutionize the design of thin-film organic photovoltaic (OPV) devices by allowing feasible manufacturing of arbitrary-shaped modules. This makes a distinction to coating methods, such as slot die coating, in which the pattern is limited to continuous stripes. Here, we analyze the thin-film formation and its influence on OPV module performance as the gravure printing of hole transport and photoactive layers are transferred from laboratory to R2R pilot production environment. Insertion of a 0.8-nm layer of lithium fluoride (LiF) as an interfacial layer between the active layer and the electron contact provided insulation against the detrimental pinholes formed in the R2R printing process. Using this device configuration, we produced well-performing R2R-printed monolithic modules with a mean efficiency of 1.7%. In comparison, reference modules with an efficiency of 2.2% were fabricated using laboratory-scale bench top sheet-level process. Surface energy and tension measurements together with optical microscopy were used to analyze the printability of the materials. The pinhole insulation was investigated in detail by processing R2R-printed OPV modules with different interfacial layer materials and performing electrical measurements under dark and AM1.5 illumination conditions. Furthermore, we analyzed the LiF distribution using X-ray photoelectron spectroscopy. The insulating nature of the LiF layer to improve module performance was confirmed by manufacturing lithographically artificial pinholes in device structures. The results show the possibility to loosen the production environment constraints and the feasibility of fabricating well-performing thin-film devices by R2R gravure printing. Copyright (c) 2014 John Wiley & Sons, Ltd.

Printed electronics and other large-area roll-roll - compatible processes are opening up the new opportunity for cost-efficient mass manufacturing of electronics among other functionalities, on large-area and flexible substrates such as plastic, paper, metal foils, glass and fabrics. Data processing power and other functionalities still require high performance microelectronics circuits and therefore, also traditional electronic/semiconductor technology are also needed. These needs lead to technical manufacturing requirements that can be fulfilled best with concept of utilization combination of printed electronics and hybrid integration of silicon electronics to flexible printed platforms. Extending the continuous roll-to-roll manufacturing approach as far as possible (in air or/and in vacuum) in the manufacturing process to assembly and bonding, the manual assembly and handling phases can be almost fully eliminated. In this paper recent development to manufacture freeform and flexible electronics components and systems using printing and hybrid integration processes is presented. Production examples of hybrid integration will be presented for 1) LED display, 2) a large area roll-to-roll processed LED luminaire, 3) over-moulded optical touch panel and 4) over-moulded OLED subassembly.

AbstractOrganic light emitting diodes (OLED) are developing rapidly and provide a huge market potential for signage, lighting and display applications. Cost efficient manufacturing of OLED components on different flexible substrates is under heavy investigation. In this paper focus is on polymer OLEDs and their non‐vacuum solution processing using roll‐to‐roll (R2R) printing techniques. In this paper VTT's R2R manufacturing process capabilities for printed OLED components are presented. Several demonstrator concepts based on printed OLED technology are introduced including; printed OLED elements 1) in a smart package, 2) a 7‐segment display integrated in a ID‐1 card, 3) an electronics voting card with OLED indicator and 4) a 35 cm2 OLED lighting element printed on glass.

This paper presents research activities carried out at VTT Technical Research Centre of Finland in the field of hybrid integration of optics, electronics and mechanics. Main focus area in our research is the manufacturing of electronic modules and product structures with printed electronics, film-over-molding and polymer sheet lamination technologies and the goal is in the next generation of smart systems utilizing monolithic polymer packages. The combination of manufacturing technologies such as roll-to-roll-printing, injection molding and traditional component assembly is called Printed Hybrid Systems (PHS).Several demonstrator structures have been made, which show the potential of polymer packaging technology. One demonstrator example is a laminated structure with embedded LED chips. Element thickness is only 0.3mm and the flexible stack of foils can be bent in two directions after assembly process and was shaped curved using heat and pressure. The combination of printed flexible circuit boards and injection molding has also been demonstrated with several functional modules. The demonstrators illustrate the potential of origami electronics, which can be cut and folded to 3D shapes. It shows that several manufacturing process steps can be eliminated by Printed Hybrid Systems technology. The main benefits of this combination are small size, ruggedness and conformality. The devices are ideally suited for medical applications as the sensitive electronic components are well protected inside the plastic and the structures can be cleaned easily due to the fact that they have no joints or seams that can accumulate dirt or bacteria.