FLEXSolar - Flexible energy
harvesting film for stand-alone microsystems
PTDC/EEA-ELC/114713/2009, 82.867€, 01-03-2011 – 31-08-2014
This
work is funded by FEDER through COMPETE funds and FCT funds in the project
PTDC/EEA-ELC/114713/2009.
The increasing
energy demand of battery-powered wireless devices requires new energy
scavenging systems, capable of harvesting energy from environment when
available and deliver it when necessary. Energy scavenging is mainly based
on thermoelectrics, vibration and photovoltaic
energy sources. In a photovoltaic scavenger, the output current and power of
the photovoltaic cells vary much as function of illumination intensity and spectra
and an energy-efficient electrical power supply from this source is difficult
to obtain under the strongly varying conditions of illumination. On the other
hand, the usual backup batteries provide voltages which decrease during
discharging of the battery. During charging, the applied voltage should also be
adapted to the evolution of the electrical potential and the stored charge. An
efficient energy scavenging system is proposed to overcome these limitations.
We propose a new approach offering an autonomous power source: a flexible thin
film device for photovoltaic (PV) energy scavenging that integrates a solar
cell, a lithium battery and electronics for maximum power point tracking (MPPT)
and battery charge. This flexible thin film stack (see annexed figure) can be
used in sensing and monitoring applications, in particular human body
applications. The device is flexible enough to be applied on a curved surface
like the human body and supply energy for autonomous wireless microsystems,
which can also be integrated in the film. The film is composed of three parts:
• A flexible
thin-film photovoltaic cell.
• A flexible
rechargeable solid-state lithium battery, fabricated by planar thin-film
technology.
• A flexible
surface-mount (SMD) electronic circuit, for DC-DC conversion and power
management that can also include application electronics for monitoring
purposes.
The inclusion of a
thin-film battery in the system adds the possibility of powering the device
when light is not available. Since many of wireless sensors are powered in a
peak basis, the battery can supply this current. Electronics and materials
engineering are involved in this project. Considering materials engineering,
two main research areas are considered: Thin-film Si photovoltaic cells and
solid-state lithium rechargeable batteries.
The main key
challenges in each area are:
• Fabrication of
thin-film Si photovoltaic cells on flexible substrates, with efficiency higher
than 5%
• Fabrication of
flexible solid-state rechargeable batteries with fast charging-time. A layered
lithium battery is proposed to decrease charge time and decrease capacity of
conventional solid-state lithium batteries.
• Electronic
circuits to charge battery with maximum efficiency using MPPT algorithm,
considering the voltage and current supplied by photovoltaic cell and provide
power (in a peak basis) and information about remaining battery charge to
application electronics.
The target
properties of this device are:
• Area of 10 cm2.
• Thickness below
2 mm of the whole film including electronic circuits.
• Unlimited number
of bending actions over a curved surface with a radius of 20 mm.
• Highly flexible
amorphous silicon-based photovoltaic cells with AM 1.5 conversion efficiency
above 5% and fill factor of 0.65.
• Battery voltage
of 4.2 V and capacity of 5 mAh,
corresponding to 0.5 mAh/cm2.
• Charge and
discharge rates up to 5C.
• Electrolyte
materials with an ionic conductivity of 2 × 10-6 S/cm at room temperature.
• Dynamic
optimization of the voltages and currents of photovoltaic cell harvesting and
battery charging.
• Supply voltage
available for the electronic application 3.3 V.
• Electrical power
conversion efficiency of 90% in average from the solar cells to the battery and
95% from battery to application electronics.
• Power management
unit uses the direct battery voltage.
• Charging time of
full battery capacity in less than 15 minutes, under direct sunlight.
An efficient energy scavenging system was proposed, offering an autonomous
power source: a flexible thin film device for photovoltaic (PV) energy
scavenging that integrates a solar cell, a lithium battery and electronics for
maximum power point tracking (MPPT) and battery charge. The film is composed of
three parts:
• A flexible thin-film photovoltaic cell.
• A flexible rechargeable solid-state lithium battery, fabricated by planar
thin-film technology.
• A flexible surface-mount (SMD) electronic circuit, for DC-DC conversion and
power management that can also include application electronics for monitoring
purposes.
• A flexible thin-film photovoltaic cell, not developed, but bought in the
market, as suggested by project evaluators.
• A flexible rechargeable solid-state lithium battery, fabricated by planar
thin-film technology
• A flexible surface-mount (SMD) electronic circuit, for DC-DC conversion and
power management that can also include application electronics for monitoring
purposes.
The achieved properties of this device are (described here in the same
order of proposed properties):
• Area of 1 cm2. (10cm2 was proposed. With equipment available, uniformity of
films could not be achieved in larger areas. However, the fabrication process
for a 10cm2 device would be the same, using larger area sputtering equipment
(Figure 6).
• Thickness of 1.6 mm of the whole prototype film including electronic
circuits. (bellow 2mm proposed). Fig 3
• Unlimited number of bending actions over a curved surface with a radius of 20
mm in the complete prototype. Radius bellow 5mm was achieved in battery film.
[P1], Fig 8 and Fig 9
• Battery voltage of 4.2 V and capacity of 10.8nA/cm2. [C1]
The smaller value of capacity is due to low thickness of films and
insufficient crystallization of cathode film. Higher capacity can be obtained
in thicker films (resulting in a longer fabrication process). Also was reported
that annealing at temperatures of 600-700 ºC results in crystalline films [P3].
This was achieved in this project using silicon substrates this process was not
compatible with flexible substrates used. Efforts are still being made to get
higher crystallization using Pulsed Laser Techniques, in a collaboration with Vigo University.
• Charge and discharge rates up to 6C. Charge from 3.4V to 3.9V in less
than 150-300 seconds. [C1]
• Electrolyte materials with an ionic conductivity bellow 2 × 10-6 S/cm at room
temperature. [P2]
• Dynamic optimization of the voltages and currents of photovoltaic cell harvesting
and battery charging. [P1, T3, T4]
• Battery voltage available for the electronic application. A fixed voltage of
3.3V was proposed, and could be obtained with an additional DC-DC converter,
but efficiency would decrease. Since the battery voltage 3.4 to 4.2V is
acceptable for a large variety of circuits, this extra DC-DC converter was not
developed.
• Electrical power conversion efficiency of 85% in average from the solar cells
to the battery. MPPT control starts with
very low light conditions, bellow 6Wm2 [P1], and voltages as low as 250mV.
• Electrical power conversion efficiency above 95% from battery to
application electronics. Internal
resistance (Battery to electronic circuit) bellow 5 Ohm and typical operating
current of 550nA. Low Battery disconnect function to protect battery from
over-discharge (<0.1nA). [T2].
• Power management unit uses the direct battery voltage.
• Charging time of battery bellow 6 minutes in the thin-film fabricated
battery. [C1]
Fig1: Power-film power and efficiency during a day
Fig3: Power-film prototype fabrication
Fig4: Power-film prototype charging in a real situation
Fig5: Battery protection. Thickness of battery film not oxidized during
exposition to air.
Fig6: Fabricated battery
Fig7: Charge/discharge curves of fabricated battery
Fig8: Prototype flexibility test
Fig9: Films flexibility test
Books
(chapt)
[L1] M. F. Silva,
J. F. Ribeiro, J. P. Carmo, L. M. Gonçalves, M. M. Silva, and J. H. Correia,
Solid state thin films lithium batteries for integration in microsystems, Book
Chapter for the upcoming issue Scanning Probe Microscopy in Nanoscience
and Nanotechnology 3. Springer, ISBN 978-3642254130, 2012
Journal
[P1]
JP Carmo, JM Gomes, LM Gonçalves, JH Correia; A flexible thin-film for powering stand alone
electronic devices, Measurement
46 (10), 4145-4151
[P2] J. F. Ribeiro,
R. Sousa, J. P. Carmo, L. M. Gonçalves, M. F. Silva, M. M. Silva, and J. H.
Correia, “Enhanced solid state
electrolytes made of lithium phosphorous oxynitride
films”, Thin Solid Films, 522,
85-89.
[P3] J.F.
Ribeiro, R. Sousa, M.F. Silva, L.M. Goncalves, M.M. Silva and J.H.
Correia, “Thin-film Materials for
Solid-State Rechargeable Lithium Batteries”,
ECS Transactions, Electrochemical Society, Vol. 45 (29), pp. 139-142, April
2013.
[P4] Ribeiro, J. F.; Sousa,
R.; Sousa, J. A.; Pereira, B. M.; Silva, M. F.; Gonçalves, L. M.; Silva, M. M.;
Correia, J.H., "Rechargeable lithium film batteries: encapsulation and
protection", Procedia Engineering, 47, 676-679,
2012.
Conferences
[C1] J.F. Ribeiro, R. Sousa, J.A.
Sousa, L.M. Goncalves, M.M. Silva, L. Dupont and
J.H. Correia, “Flexible Thin-Film
Rechargeable Lithium Batteries”, Transducers2013, Barcelona, Spain, June
16-20, 2013.
[C2] J.F. Ribeiro, R. Sousa, L.M. Goncalves,
M.M. Silva, L. Dupont and J.H. Correia, "Lithium cobalt oxide deposited on polyimide
substrate", 13th European Vacuum Congress (EVC13), Aveiro,
Portugal, September, 2014.
[C3] J.F. Ribeiro, R. Sousa, J.A. Sousa,
L.M. Goncalves, M.M. Silva, L. Dupont and
J.H. Correia, “Thin-Film Lithium
Batteries Materials”, Vacuum2013, Paris, France, September 09-13, 2013.
[C4] R. Sousa, J.F. Ribeiro, J.A. Sousa,
R.T. Montenegro, L.M. Goncalves and J.H. Correia, “Silicon nitride thin-films by RF sputtering: application on solid state
lithium batteries”, MME2013, Hanasaari, Finland,
September 1-4, 2013.
[C5] R. Sousa, J.F. Ribeiro, J.A. Sousa,
L.M. Goncalves, J.H. Correia, “All-solid-state
batteries: an overview for bio applications”, Bioengineering 2013, Braga, Portugal, February 20‑23,
2013.
[C6] Ribeiro, J. F., Sousa, R.,
Sousa, J. A., Pereira, B. M., Silva, M. F., Goncalves, L. M; Correia, J. H. “Rechargeable lithium film batteries–encapsulation and
protection”,. Eurosensors
2012, Krakow, Poland, September 9-12, 2012
[C7] J.F.
Ribeiro, Rui Sousa, J.A. Sousa, B.M. Pereira, M.F. Silva, L.M. Goncalves, M.M.
Silva and J.H. Correia, “Encapsulation
of Rechargeable Solid-State Lithium Batteries”, 222nd ECS Meeting(PRIME),
Honolulu, Hawaii, USA, 2012.
[C8] J. F.
Ribeiro, M. F. Silva, L. M. Goncalves, M. M. Silva, J. P. Carmo and J. H.
Correia, “Layered materials for solid-state rechargeable lithium batteries”,
221st ECS Meeting, Seattle, USA, May 6-10 2012.
[C9] J. C.
Ribeiro, M. F. Silva, J. F. Ribeiro, L. M. Goncalves, J. P. Carmo, J. H.
Correia, M. M. Silva, F. Cerqueira, P. Alpuim, J.-E. Bourée, “Thin-film solid-state rechargeable lithium
battery”, Proceedings of MME 2011, pp. 190-193, Toensberg,
Norway, 19-22 June 2011
[C10]
J. F. Ribeiro, M. F. Silva, L. M. Goncalves, J.P. Carmo, J. H. Correia,
“Thin-film improved materials for solid-state lithium batteries”, Proc. of
Materials 2011, pp.1, Guimaraes, Portugal, 18-20
April 2011.
Finished Mscs
[T1] MscThesis Sensores sem fios autónomos,
alimentados por painel solar e microbateria de lítio, com controlo de alimentação
através de circuitos MPPT de baixa potência, Avelino Araújo Ferreira, MIEEIC,
Início 1-11-2010 fim Dez2012
[T2] MscThesis Power-Film:
Um filme flexível autónomo para alimentar dispositivos elétricos, José Miguel
Sousa Gomes, Mestrado Integrado em engenharia electrónica
e de computadores da UM, 01-11-2010 a 2-05-2012
[T3] MscThesis “Conversor DC-DC em tecnologia CMOS
para energy harvesting”,
Mestrado Integrado em engenharia biomédica, Fernanda Guedes, Out 2011-Out 2013
[T4] MscThesis Implementação de um sistema MPPT, em
circuito integrado CMOS, Nilton César Lima Lopes, MIEEIC, Início 1-11-2011 -
2013
[T5] MscThesis Bateria de lítio em
filme fino - Fabrico e caracterização de novos materiais para utilização no
ânodo, José Augusto Fonseca de Sousa, MIEIC, Início 1-11-2011-2012
[T6] MscThesis Bateria de lítio em filme fino –
Fabrico e caracterização do cátodo em substrato flexível, Rui Pedro Pereira da
Costa, MIEEIC, Início 1-11-2011- 27/12/2013
[T7] MscThesis Proteção de uma
bateria de lítio em filme fino, Bruno Miguel Oliveira Pereira, MIEEIC, Início
1-11-2011-2012
New Equipment
Magnetrão TORUS 2HV, AXIAL MNT, 10"TUBE, STD Magnet assy, Swing shutter
Exterior
da câmara (esq) e magnetrão no interior da câmara de
deposição (dir)
Equipamento
para posicionamento e aquecimento de substrato em camara de deposição
(no
interior da câmara de deposição)
Sistema com sensor para medição do oxigénio,
IONIC SYSTEMS GMBH
Este trabalho é financiado por Fundos FEDER
através do Programa Operacional Factores de Competitividade – COMPETE e por
Fundos Nacionais através da FCT – Fundação para a Ciência e a Tecnologia no
âmbito do projeto PTDC/EEA-ELC/114713/2009.
