The main aim of HIFLEX was to develop a cost-effective Highly Flexible Printed ITO-free Organic Photovoltaics (OPV) module technology matching the particular requirements of mobile and remote ICT applications, simultaneously delivering the required efficiency under different light conditions, sufficient lifetime, acceptable cost structure, appropriate power-to-weight ratio and fit-to-purpose mechanical flexibility.
Existing “grid-dependent” and future energy autonomous ICT applications cover a broad range of products. These are “classical” applications such as: PDAs, laptops and mobile phones, but also future applications like wireless sensor networks, e-labels, epackaging, e-posters, smart blisters and smart bandages. Most of these applications will have low power consumption and may be based on printed electronics in the future. Their usage would be more versatile and have a high degree of comfort if they could be self-supporting in their energy supply and thus the benefits gained through integration of OPV modules would be obvious.
An application-driven research approach was followed by developing large area, solution processable ITOfree OPV using scalable, reproducible and commercially viable printing and coating techniques enabling the low-cost production of highly flexible and lightweight OPV products.
In order to construct an energy autonomous system powered by light energy, the implemented solar cell technology has to fulfil certain requirements. The general requirements that a solar cell technology has to fulfil in order to add value to the product are:
- High power-to-weight ratio and power conversion efficiency
- 1-5 year lifetime
- Maximum of 10 Euro per Watt peak (Wp)
- High mechanical flexibility
- High ambient light efficiency
- Versatile module concepts
- Technological compatibility
The work that has been performed in HIFLEX varied from designing and fabricating various ITO-free device architectures using optimized electrodes based on printed current collecting metal grids and highly conductive PEDOTs, development of fabrication technologies for optimal S2S and R2R processing of OPV, electrical modelling to design optimal cell and module structures for ITO-free device concepts and experimental validation, evaluation of large area characterization methods for process control, stability testing, life cycle and cost assessment and market evaluation studies.
The combined efforts of the consortium have led to a number of important achievements that will form an essential basis for creating an economically accessible and widely applicable OPV technology for a range of future applications:
- Power conversion efficiencies measured at STC, range between 1 and 2.5% for the different ITO free device concepts using P3HT:C60-PCBM as the photoactive layer
- Lifetime tests revealed some ITO free device concepts are more stable compared to ITO based polymer solar cells aged under identical conditions
- OPV Modules down to 12 m substrate thickness can be manufactured both on S2S and R2R scale without considerable loss in performance
- Very good efficiencies up to 6% under low, fluorescent light conditions have been achieved for selected ITO free OPV based designs based on P3HT:PCBM.
- Excellent stabilities of encapsulated modules under various indoor accelerated and outdoor lifetime testing conditions have been demonstrated.
- 250 CE labelled functional credit card sized laser pointers have been manufactured using ITO free OPV modules as the final demonstrator of the project