Seminar on Quantum Efficiency Measurements in Solar Cells

Quantum efficiency is a key factor to determine the conversion from sun light to electrical energy. It is essential characteristic of solar cells design. The seminar on Quantum Efficiency Measurements in Solar Cells was organized by PV Test Laboratory of Hong Kong Science and Technology Parks (HKSTP) on 31 March 2011.

The speaker was Dr. Pawan Bhat (Founder and Chief Technology Officer, ProtoFlex Corporation) and he introduced the testing of quantum efficiency on solar cells included theory and some applications.

Quantum Efficiency (QE) is the ratio of the number of electrons which exit the solar cell per incident photon at each wavelength.

There were two types of QE. One is external quantum efficiency (EQE) and the other is internal quantum efficiency (IQE).

Then Dr. Bhat introduced the structure of solar cells. He explained the light trapping in thin-film silicon solar cells for superstrate and substrate configurations

The calculation of IQE derived a diffusion length was discussed.

The following diagram showed diffusion length from the slope of the inverse IQE-1 plotted against the optical absorption length.

It showed the different bias for carrier injection and real solar cell conditions.

The different samples' QE measurement spectrum were showed including Mono-Si, CIGS, GaAs and a-Si:H.

Hybrid material cell was demonstrated (e.g. A-Si:H/micro-Si:H TANDEM).

The QE equipment was described.

Q&A Session.

After the theory session, the practical session was performed in the Photovoltaic Test Laboratory (PVTL).

Reference:

Photovoltaic Laboratory (PV Test Lab) of Solar Energy Technology Support Centre (SETSC) - http://lab.hkstp.org/e/default_home.asp?url=/e/customize/analysis_solar.asp

ProtoFlex Corporation - http://www.protoflexcorp.com/

Measuring Solar Energy Properties of Photovoltaic (PV) Materials

The seminar entitled “Measuring Solar Energy Properties of Photovoltaic (PV) Materials” was held on 23 July 2010 in Hong Kong Science and Technology Parks (HKSTP).
The speaker was Ms. Michelle Lee (Specialist, PerkinElmer (Hong Kong) Limited). The content was summarized below.


In the beginning, Ms. Lee introduced different analytical technique employed in each stage of silicon-based PV cells process.

The following slides showed the properties of the incident light through a material.

The speaker introduced UV/VIS/NIR spectrometer which can help to measure these properties. The PerkinElmer Lambda series spectrophotometer with 150mm integrating sphere was used in PV Test Laboratory in HKSTP.

Ms. Lee explained why we needed to use integrating sphere because of sampling errors during material measurement.

There were four types of measurements: Transmission (T), Diffuse Reflectance, Total Reflectance (R), Absorptance (A) and Haze.

Absorptance is the percentage of energy incident on a specimen that is not directly transmitted or reflected

The expression is described as: T + R + A = 1 or
%Absorptance = 100% - Direct Transmission - %Reflected

The Haze Measurement was based on ASTM 1003-92 and shown as follow.

Then, Ms. Lee briefed the application of solar measurements on Architectural Glass, which can control the transmission of visible light, total solar energy and longer wave thermal radiation within wide limits to reduce energy consumption for the regulation of temperature in a building. Reflectance and transmission are important parameters of architectural glass.

Finally, PV Cell Properties Measurement was discussed.

Triple junction solar cell design was shown. Multiple layers of thin films can produce very complex interference patterns.

For more information:
ASTM E 903-96: Standard Test Method for Solar Absorptance, Relflectance, and Transmittance of Materials using Integrating Spheres.
ASTM E 424-71: Standard Test Method for Transmittance and Reflectance (Terrestrial) of Sheet Materials.
ASTM E 490-73: Standard Solar Constant and Air Mass Zero Solar Spectral Irradiance Tables
ASTM E 891-87: Standard Tables for Terrestrial Direct Normal Solar Spectral Irradiance for Air Mass 1.5
ISO 9050 / EN 410: Glass in building – Determination of light transmittance, solar direct transmittance, total solar energy, transmittance and ultraviolet transmittance, and related glazing factors.

PV Optics software: http://www.nrel.gov/pv/measurements/computational_modeling.html

PerkinElmer Application Note for UV/Vis/NIR Spectrometer:
Dharma J. & Pisal A. (2009) “Simple Method of Measuring the Band Gap Energy Value of TiO2 in the Powder Form using a UV/Vis/NIR Spectrometer”

Solar Simulator Standard Testing for Solar Panels

I attended the seminar entitled “Solar Simulator Standard Testing for Solar Panels” which organized by Solar Energy Technology Support Centre (SETSC) of Hong Kong Science and Technology Parks (HKSTP). The content was summarized for sharing below.

Ms. Abby Chen (Development Engineer, All Real Technology Co. Ltd., Taiwan) was the trainer presented the principle and operation of the steady state solar simulator for I-V measurement.


Overview of Solar Energy related standards were briefed.

Measurement standard:
- IEC 60891 Photovoltaic devices – Procedures for temperature and irradiance corrections to measured I-V characteristics
- IEC 60904-1 to -10 Photovoltaic devices

Quality standard:
- IEC 61215:2005 Crystalline silicon terrestrial photovoltaic (PV) modules –Design qualification and type approval
- IEC 61646:2008 Thin-film terrestrial photovoltaic (PV) modules - Design qualification and type approval
- IEC 62108:2007 Concentrator photovoltaic (CPV) modules and assemblies – Design qualification and type approval

Safety standard:
- IEC 61730:2007 Photovoltaic (PV) module safety
- UL 1703:2002 Flat-Plate Photovoltaic Modules and Panels
- TUV Class II – Safety Class II testing of PV Modules

IEC 60904-9:2007 Photovoltaic devices –Part 9: Solar simulator performance requirements were mentioned.
The purpose of this standard is to define classifications of solar simulators for use in indoor measurements of terrestrial photovoltaic devices, solar simulators are classified as A, B or C for each of the three categories based on criteria of spectral distribution match, irradiance non-uniformity on the test plane and temporal instability.

Definition of solar simulator classifications was shown.

Spectral match of a solar simulator is defined by the deviation from AM 1,5 reference spectral irradiance as laid down in IEC 60904-3.

Non-uniformity (%) = { (max irradiance – min irradiance) / (max irradiance + min irradiance)} x 100%

Temporal Instability (%) = { (max irradiance – min irradiance) / (max irradiance + min irradiance)} x 100%
It is defined by two parameters below:
Short term instability (STI)
Long term instability (LTI)

The simulator classification example is shown as follows:
Spectral match is C: 1.74 in 900 – 1100 nm (worst case)
Non-uniformity is B: 2.8%
Temporal instability is B: STI – 0.5% (A) but LTI – 3.5% (B)
Then the simulator is classified as CBB.

Safety operation practices were briefed.
The lamp may explode in either the hot or cold state (Wear face mask when examining the lamp house or the lamp bulb)
Check the windlass lock position before and after loading PV module)

Solar Simulator Illumination Principle was mentioned.

Each single lamp set illuminates the same area (the whole effective test area) on the testing plane

She introduced Solar Simulator operation process and the standards IEC 61646:2008 & IEC 61215:2005.

10.4 Measurement of temperature coefficients

10.6 Performance at STC and NOCT
Performance at STC: 1000W/m2, close shutter until stable; keep module below 25C; open shutter and illuminate it up to 20C, using I-V Tracer measure the characteristic of the curve
Performance at NOCT: 800W/m2, close shutter until stable; keep module below NOCT; open shutter and illuminated up to NOCT, using I-V Tracer measure the characteristic of the curve

10.7 Performance at low irradiance
Using 200 W/m2, close shutter until stable; keep module below 25C+2C; illuminate it up to 25C+2C; using I-V Tracer measure the characteristic of the curve

10.9 Hot-spot endurance test
Condition: 800-1000W/m2, I-V Tracer P>0.99Pmax1; shade a cell and measure the following parameters.
α: Temperature coefficient of Isc
β: Temperature coefficient of Voc
δ: Temperature coefficient of Pmax

10.19 Light-soaking

Testing equipment included
- Class BBB solar simulator (IEC 60904-9)
- I-V Tracer (IEC 60904-1)
- Reference Device (IEC 60904-2)
- Thermometer and temperature control system
- Shutter, etc.


Laboratory Practice Section

Mr. Li-Yuan Liao (Assistant Manager, All Real Technology Co. Ltd., Taiwan) demonstrated how solar simulator work in PV test laboratory in HKSTP.

Setup Solar Panel

Turn on the Solar Lamps

Measure the I-V curve

Background information:

For PV testing (terrestrial use), the Standard Test Condition (STC) is defined as an insolation of 1000W/m2 (1 SUN) at 25 °C and with a solar spectral distribution equivalent to global AM1.5, per ASTM G173-03 and IEC 60904-3.
(Air Mass is the measure of how far light travels through the Earth's atmosphere. One air mass, or AM1, is the thickness of the Earth's atmosphere. Air mass zero (AM0) describes solar irradiance in space, where it is unaffected by the atmosphere. The power density of AM1.5 light is about 1,000W/m2; the power density of AM0 light is about 1,360W/m2, which is considered to be the solar constant.)

Normal Operating Cell Temperature (NOCT): The estimated temperature of a solar PV module when it is operating under 800 W/m2 irradiance, 20°C ambient temperature and a wind speed of 1 meter per second. NOCT is used to estimate the nominal operating temperature of a module in the field.


For more information:
HKSTP Laboratory: www.lab.hkstp.org
All solar related IEC standards mentioned in the seminar.

Conference on “Solar Photovoltaic Energy (PV) – From Technology to Business Opportunities”

The conference “Solar Photovoltaic Energy (PV) – From Technology to Business Opportunities” was held on 14 April 2009. The Hong Kong Electronics Industry Association (HKEIA), in collaboration with the HKSTP, sponsored by the Innovative Technology Commission, has organized the conference to be held concurrently with the Hong Kong Electronics Fair. I would like to summarize some key points of each topic as follows:

In the beginning, Prof. K.B. Chan (Chairman – Hong Kong Electronic Industries Association) gave a Welcome Remarks to introduce this hot topic “Renewal Energy”.


Mr. Eddy Chan (Commissioner for Innovation and Technology) presented an Opening Remarks about ITC funding support. And he ran through the early application of solar cell on calculator in 1970s.


Then Mr. Anthony Tan (CEO – HKSTP) presented another Opening Remarks to make aware of Green Energy focus in Science Park, especially the opening of Solar Energy Technology Support Centre (SETSC) on 20 March 2009. It would complete the value chain from R&D in HKSTP and manufacturing in Industrial Estate or Pearl River Delta . Now, HKSTP is focusing on the phase III development.

Before others presentation, it was time for Souvenir Presentation and Group Photo.

Appreciation to Ir. Allen Yeung

Appreciation to Prof. YC Chan

Group Photo

The first speaker was Prof. Ng Ka Ming (CEO – NAMI R&D Centre, HKUST) and his topic was “Materials Development in PV Applications”.

He introduced different types of Solar Cells including:
i) Wafer (Efficiency%): Monocrystalline Si (~25%), Polycrystalline Si (~20.4%), Crystalline GaAs (~26.1%) and Polycrystalline GaAs (~18.4%).
ii) Thin film (Efficiency%): a-Si (~9.5%), μc-Si (~10.1%), GaAs (~26.1%), CIGS (~19.4%)and CdTe (~16.7%).
iii) Multijunction (Efficiency%): a-Si /μc-Si (~11.7%) and GainP / GaAs / Ge (~32%).
iv) Organic solar cell (Efficiency%): Dye sensitized (~10.4%) and Polymer (~5.15%).

Then he pointed out the advantages of thin film silicon solar cells as follows:
· Consume less silicon (Thin Film used below 2μm (μc-Si), 200nm (a-Si); and wafer used about 180μm)
· Good energy payback time
· Suitable for flexible substrates
· See-through capacity for BIPV

However, the efficiency depended on materials and processing. Some methods have been investigated such as metal induced crystallization (MIC), laser crystallization and solid phase crystallization.
Finally, speaker showed the future development of solar cell which efficiency could over 40%!

The second speaker: Prof. Zao Ying (Vice-Chairman, Chinese Renewable Energy Society and Deputy Director of PV Committee) come from Nankai University.
Topic: “China Market on PV”.

Firstly, he mentioned the advantages and disadvantages of solar cells. The major disadvantages were identified as:
i) Energy was discontinuity
ii) Large scale energy storage technology was not mature
iii) Small scale energy storage was expensive and short life time
iv) Cost was too high

The most important China PV policy was announced on 26 March 2009.
"財政部頒布 <關于加快推進太陽能光電建築應用的實施意見＞，及＜太陽能光電建築應用財政補助資金管理辦法＞，以推進太陽能光電技術在城鄉領域的應用． "

The third speaker: Ms. Daniela Schreiber (Head of Strategic Operations, EuPD Research EuPD).Topic: “Global Market (EU &US) on PV”

She revealed that EuPD Research is an international market research and consulting firm and more than 270 PV research & consulting projects successfully accomplished since 2001. The she indicated the trends in markets segments in Europe and predicted the top 4 markets (France, Germany, Italy and Spain) in 2009 to 2012.

She concluded that USA, Japan or China would most probably gain momentum, but not before 2010. And the US market differed significantly from its European in “Complex promotion condition”; “Size & sales channel architecture” and Special product preferences”.


The forth speaker: Mr. George So (General Manager and Global Director of Sales, DuPont Apollo Limited). He presented the topic entitled “Reaching For A Green Future”.

He demonstrated the relationship between energy and the rise of the Great Nations (A correlation between energy policy vs. human civilization, national security and economic development)

Then he introduced DuPont Apollo which was founded in April 2008. Its Headquarter and R&D Center are in Hong Kong Science Park (with area 14,600 sq. ft.) and Manufacturing Site is in Guangming District, Shenzhen (with area 50,000m2) for Thin Film PV Module.

He explained that the conversion efficiency was measured at STC (AM1.5, 1000W/m2, 25oC) that higher efficiency in c-Si than a-Si TF. But a-Si TH has better temperature coefficient and irradiation coefficient. Therefore, a-Si TF is found to be higher conversion efficiency for the whole day consideration.


The fifth speaker: Dr. Yuan Lee (Chairman – Terra Solar Global).
Topic: “PV 2.0: Trends and The Framwork to Advance”.

He said that “The Photovoltaic Technology of Choice for the Future, thin films are on a steep adoption curve”. He gave an example that the forecasted PV market size in 2005 was 300MW but the actual PV market growth in 2005 was close to 1GW! So long-term growth far exceeds all expectations. He also introduced the PV framework which included module manufacturing, PV system integration and PV applications.

Finally, he presented the following sentences as conclusion:
A lesson taken from evolutionary theory: the survivors are not the most adapted, but the most adaptable. “We need to embrace the complexity of the solar business.”


The sixth speaker: Ir. Allen Yeung (Vice-President, Business Development and Technology Support) from HKSTP.
Topic: “PV Pilot Line & Test Lab”.

He introduced different technology support services provided by HKSTP in five clusters including Electronics, ITC, Precision Engineering, Biotech and Green-Tech. Then Hong Kong solar energy applications on PV were also presented.

The major steps of Pilot Line production were shown as “Glass Gleaning & PECVD Procedure”, “Soldering & Wire Bonding Procedure” and “Lamination Procedure”.

After that he mentioned the PV Test Laboratory, especially in Safety and Performance Testing (e.g. IEC 61646) which is separated into 4 major parts. They are:
· Inspection and Wet Operating Condition
· UV Pre-condition Test
· Temperature and Humidity Test
· Mechanical Test

Finally, he quoted Mr. Donald Tsang’s (CE, HKSAR) speech for the opening of SETSC on 20 Mar 2009 as conclusion. That is “There is much work to be done in harnessing the power of the sun in an efficient and cost effective way. I assure you the Hong Kong government will continue to promote the development and use of clean energy sources at every opportunity. This is a very exciting beginning.”

The last speaker was Prof. YC Chan (Director – EPA Centre, CityU) and his topic was “Advanced EPA Techniques for Photovoltaic Applications”.

He identified 3 major problems in PV solar modules. They were:
· How to chose the best technology
· How to overcome the reliability problem
· How to fit the solar cell system into grid

He also discussed the improvement of cost-efficiency of PV module:
i) To develop advanced materials and devices for low cost and high conversion efficiency PV cells
ii) To produce highly reliable PV devices

For overcoming the reliability problem, 5 types of tests are needed:
i) Indoor Environmental Tests
ii) Indoor Accelerated Tests
iii) Outdoor Tests
iv) Failure Analysis
v) Module Characterization

Lastly, Prof. Chan concluded two points with:
i) Need for dedicated support in PV such as provide dedicate total solutions on site for PV applications and customize the PV products for local environment and uses.
ii) Advantages of having a dedicated PV support such as fast turn around time and round the clock support.

One stop shop full services in FA and Reliability for PV applications in HKSTP has been provided for PV industry.

At the end, speakers answered the participants’questions in discussion panel section.

Solar Cell Simulation

Synopsys TCAD Seminar was held on 18 Dec 2008 in HKSTP. One of sessions was Solar Cell Simulation and the speaker was Mr. John Wang (Product Marketing Manager, Synopsys Taiwan Limited). I had summaries some points below.

TCAD is Technology CAD used computer simulation to model semiconductor process and device technologies. The current solar cell technologies are:
· Silicon-based Cells
- Crystalline silicon (c-Si)
- Multi-crystalline silicon (mc-Si)
- Amorphous silicon (a-Si)
· Compound Semiconductor
- Single and multi-junction: GaAs, InGaP
- CdTe
- CIGS: Cu(In, Ga)Se2
· Emerging Technologies
- Organic semiconductors
- Quantum well, dots, etc.

Using TCAD in Solar Cell Design can allow designers to optimize efficiency and enable virtual exploration of new cell designs. That process simulation can be applied to silicon-based solar cells. Some applications are shown as follows:
- Fe Concentration
- Advanced Geometric Modeling
- Solar Spectrum
- Anti-Reflection Coating (ARC) Optimization
- External / Internal Quantum Efficiency, etc.

Several research publication:
- Wyatt K. Metzger (2008) “The potential and device physics of interdigitated thin-film solar cells” Journal of Applied Physics, Vol 103
- J. Dicker, et al. (2002) “Analysis of one-sun monocrystalline rear-contacted silicon solar cells with efficiencies of 22.1%” Journal of Applied Physics, Vol 91
- P.S. Plekhanov, et al. (1999) “Modeling of gettering of precipitated impurities from Si for carrier lifetime improvement in solar cell applications” Journal of Applied Physics, Vol 86

Comments from Dr. Kitch Wilson in LinkedIn:

An industry accepted software suite used to simulate the semiconductor physics of a solar cell is available free. It is called PC1D and can be downloaded from: www.pv.unsw.edu.au/links/products/pc1d.asp

Also, a very good tutorial that covers some of the simulation equations can be found at http://pvcdrom.pveducation.org/index.html

Innoasia 2008 Conference: Renewable Energy

I joined the Renewable Energy Theme of "InnoAsia 2008 Conference: Enabling Sustainability" on 10 Dec 2008. It was summarized in follows.


The first speaker was Dr. Douglas Muzyka (Corporate Vice President & President for DuPont Greater China). His topic was “DuPont & Renewable Energy: Photovoltaics & Biofuels”.



First of all, Dr. Muzyka presented DuPont’s vision “To be the world’s most dynamic science company, creating sustainable solutions essential to a better, safer, healthier life for people everywhere.” Then he introduced “Three Growth Strategies”:
i) Put our Science to work
ii) Go where the Growth is
iii) Use the power of One DuPont

He explained the key drivers of BioFuels, i.e. Energy security / energy diversity, CO2 reduction, Sustainability, Low cost carbon and Best option for transportation market. He summarized Biofuels in 3 points:
i) Strong belief in the future of biofuels
ii) Committed to decoupling food and fuel supply chains
iii) Technology is still in its early stages but advancing rapidly

Dr. Muzyka introduced Photovoltaics Market and Industry. Then he stated the technology of Solar cell including:
i) Encapsulation
ii) Metallization
iii) Backsheets
Lastly, he said that we’re turning solar possibilities into everyday realities.

The second speaker was Prof. Junhao Chu (Member of the Chinese Academy of Sciences; Director of Shanghai Center for Photovoltaics, China) and his presentation entitled “Photovoltaic – a New Active Opportunity in China”.

Prof. Cui gave introduction of the photovoltaic industry and market development in China. The following photos show the distribution of Solar Energy in the World and in China, respectively.

Then he presented different technologies of solar cell. And he pointed out several problems as follows:
i) Backward Technology:
· Energy consumption for the world’s advanced level of 1.5 to 2 times
ii) Pollution:
· Tail gas recovery and circulating utility
iii) Small Industry Scale:
· The capacity is 400t and the actual output is 300t in 2006
iv) Cheap Substitute Technology

He mentioned “The a-Si Thin Film Solar Cell Industry is developing quickly because of low cost”. And “The module price may be 1~1.5 $ / Wp in the future with the development of technology and supply of crystal silicon materials.”

Finally, he summed up the key factors for technology development tendency:
i) Continuously improve the efficiency;
ii) Continued reduce thickness of wafer;
iii) Enlarge the economics of scale to reduce costs;
iv) Continuously improve industrialization technology.

The third speaker was Dr. Thomas Hinderling (CEO, Swiss Centre for Electronics & Microtechnology, Inc. (CSEM), Switzerland). His topic was “Solar Island”.

Dr. Hinderling described the energy coming the sun was enormous but area density of this energy (~ 1 Kilowatt per square meter) was limited. Therefore, he raised two problems had to be solved:
i) Very large “free” surfaces with high solar irradiation required to be found
ii) Solar energy required to be cost-competitive to today’s energy sources – without government subsidies

Needed surface for PV power generation to supply Hong Kong was almost its total area!

He proposed to use a huge Solar Islands on High Sea and/or on Land to collect sunlight. A prototype had being constructed in Ras al Khaimah, U.A.E.