Lithographically Printed Voltaic Cells
Sustainability and printed electronics D. Southee, P.S.A. Evans, D. Harrison & G.I. Hay Cleaner Electronics Research Group School of Engineering and Design Brunel University
Sustainability Sustainability - meeting the NEEDS of today without compromising the ability of future generations to meet their needs (from the Brundtland Report) Example of Intergenerational Equity
Maslow s s Hierarchy of Needs Self actualisation (realising one s s full potential) Aesthetic Needs Cognitive Needs Esteem Needs Love and Belongingness (Receiving and giving love and affection) Safety Needs Physiological Needs (food, water, etc)
Printed Electronics Today An enabling technology that is starting to help to meet some of these human needs But is it more sustainable than the conventional technology it replaces?
Study on environmental impact of PCB replacement by printed circuit
Environmental Impact Evaluation of Additive Circuit Fabrication Processes Ramsey, Harrison Conclusions: Reduction of the discrete processes necessary during manufacture and elimination of the wet chemical etching, plating and cleaning phases. A reduction by an order of magnitude of the cost of disposal of hazardous waste generated. A reduction in the volume of raw material which has to be processed to extract the metal for the conducting elements. A reduction in the time per unit for manufacture (reduced energy overhead).
These characteristics indicate the Conductive Lithographic process is likely to be more environmentally benign for PCB production than conventional PCB manufacture.
In the longer term, is there enough material, and is there enough energy to sustain the processes? Example A common approach to conductive tracking in printed electronics is based on conductive silver inks. Is this the right approach, or are other materials more sustainable Various experts have maintained that the entire world supply of above ground,refined silver is about 300 million ounces Others have estimated that above ground silver may be as large as 4 billion ounces,
A more sustainable alternative might be based on aluminium in its recycled form it only has embodied energy of 9 MJ/ kg, - and it is present in the earths crust in vast quantities (But its oxide layer makes conductive ink formulation challenging)
Is there enough oil left to power the processes, and provide raw materials for organic electronics? In theory we have 50,000 years left of fossil fuel deposited in the earths crust (But it s s not accessible, and burning it would use up all the oxygen in the atmosphere). Accepting a 10% reduction in oxygen level would allow 5,000 years of fossil fuel use.
Data from Global Energy Perspectives
consumption Gtoe/pa resource base additional occurrences oil conventional 3.2 295 - oil unconventional - 525 1 900 gas conventional 1.7 420 - gas unconventional - 450 400 methane hydrates - - 18 700 coal 2.2 3400 3000 uranium 0.5 263 150 U in fast breeder - 15 540 8900 Total 7.5 15958 33 050 Source: Global Energy Perspectives
Prospects for Printed Electronics Printed Solar cells - a route to low carbon energy (Konarka cells offer 3-3 5% efficiency, but ink jetted cells only 1cm2 at present) Printed Lighting prospects of large area printed lighting systems, perhaps with a factor 10 improvement in efficiency over incandescent bulbs Printed Batteries - more sustainable than current technology?
Lithographically Printed Voltaic Cells What? Investigate the fabrication of voltaic cells (electric cells & batteries) by the offset lithographic printing process Why? Offset lithography has been adapted to manufacture electronic components and circuit interconnect on a wide range of flexible materials. Costly additional processes and materials required for power Market surveys suggest that this is an obstacle to the potential uptake of the technology
LPVC Project Overview Work has been carried out on ink formulations suitable for offset lithography to enable the manufacture of Carbon Zinc cells Voltaic cells have been manufactured and evaluated
1 st Iteration Cells 1.5V but very low current..due to electrode resistance 1.5 V achievable 2 na current
Internal Resistance Simplified electrical model of cell Ra the resistance of the electrochemical path including the electrolyte and the separator Rm - is the resistance of the metallic path through the cell including the terminals, electrodes and interconnect Cb - the capacitance of the parallel plates which form the electrodes of the cell. Ri - is the non-linear contact resistance between electrode and the electrolyte.
2 nd nd Iteration - Electrode Development Anode and cathode structures printed on substrate over highly conductive silver base. Silver base layer employed as connection terminals Membrane placed above electrolyte Zinc anode (-)( ) structure placed above membrane
Typical Carbon Zinc Discharge Eveready Carbon Zinc (Zn/MnO²) Application Manual Eveready Battery Co. Inc. 2001
2 nd Iteration Printed Cell Characteristics Printed cell discharge curve through 1kΩ load
3 rd Iteration Printed Cell Characteristics Printed cell discharge curve through 5kΩ continuous load
Current Structures I. LPVCs with useful capacity demonstrated II. Manufacturing methods and activation mechanisms under investigation Battery of LPVCs powering conventional electronic system
Conclusions