Our research priorities

Martin Green started photovoltaic research at UNSW in 1974. Since this time UNSW has continued to be the world leader in photovoltaic research, holding the world record for the highest efficiency silicon solar cell for over three decades. Other world records include a 34.5% efficient one-Sun PV module, a 12.1% efficient large area perovskite solar cell, and a 10.9% efficient CZTS solar cell, all of which were achieved in 2016 or 2017. UNSW has world class research laboratories for early technology readiness level (TRL) research, complemented by a state of the art, on campus industrial R&D pilot line for silicon wafer solar cells focused on commercialising our technologies.

More detail about all our research activities can be found below.

Our school is working on various technologies to further improve the energy conversion efficiency of silicon solar cells. A large part of this work is done at our solar industrial research facility (SIRF) and often done in close collaboration with the photovoltaic industry.

 

Industrial silicon solar cells

PERC Solar Cells, including laser doped selective emitter PERC

Being the inventor of the PERC solar cell, UNSW has extensive experience in the industrial optimisation of this solar cell design and can also assist with the implementation of the Laser Doped Selective Emitter (LDSE) structure to avoid using expensive silver paste. The LDSE technology has many advantages over traditional screen printed technology including higher efficiency and lower cost. UNSW has achieved more than ten world records in conjunction with many industry partners for commercial p-type devices including the world’s first 20% efficient p-type PERC and the current world record for p-type PERC at 25%.

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Advanced hydrogenation of silicon solar cells

Advanced hydrogenation involves controlling the charge state of hydrogen atoms which has an enormous impact on their mobility and reactivity and their corresponding ability to passivate defects. This process has been shown to eliminate carrier (or light) induced degradation in p-type Cz solar cells and is ready for licensing. UNSW has also solved carrier induced recombination in multi-crystalline silicon, and this technology will be available for licencing from mid-2017.

The next step in the advanced hydrogenation project will be to use hydrogen to passivate impurity and structurally related defects up to orders of magnitudes better than can be done using conventional techniques, thus allowing the use of significantly cheaper silicon wafers for the fabrication of high-efficiency silicon solar cells. The technology can be applied to any silicon material or wafer type of either polarity, and the consensus is that this will be a prerequisite for all industrial high-efficiency solar cells (e.g. PERC and PERL). The initial “mother” patent was awarded in 2015 and many subsequent patents have since been filed, giving UNSW a unique IP position in this field. More than 10 of the world’s largest cell manufacturers have already signed licenses and agreements for the use of this technology. Scientia Professor Stuart Wenham was awarded the prestigious 2013/14 IET A F Harvey Engineering Prize for this research.

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Commercial tool design and development

UNSW has worked closely with numerous equipment manufacturers in designing and developing tools for the large-scale manufacturing of various novel UNSW technologies. These include specialised tools for light-induced plating, bifacial cell plating, rear etching, laser-doping, advanced hydrogenation, adhesion testing, and the solving of LID in both p-type multi and mono cells.

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Advanced surface and contact passivation

To further improve the efficiency of silicon solar cells it is necessary to reduce the electrical losses at the surfaces and specifically the contact between the semiconductor and the metallisation. Current technology has pushed this to the limit and new disruptive solutions are now required. As a result, there is a high interest in the silicon photovoltaic community to develop advanced surface passivation layers and so-called passivating contacts. For surface passivation films the objective is to reduce the minority carrier recombination rate as much as possible. For passivating contacts in addition the majority carrier resistance needs to be a as low as possible to ensure a maximum selectivity for the desired charge carrier. Typically this is done by using ultrathin stacks of various materials. At SPREE we mainly focus on plasma enhanced chemical vapour deposition and atomic layer deposition to synthesise these novel surface passivation and contact materials.



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Metal plating

As silver paste used to form the metal contacts in solar cells is a significant part of the overall cell cost, plating can potentially reduce the cost of manufacture. Also, plating allows very fine metal lines to be achieved thereby reducing the shading of the front surface and allowing maximal light to enter the solar cell. UNSW has had a long history of using metal plating to form the contacts of silicon solar cells. Back in the 1980s, UNSW developed the buried contact solar cell which was subsequently licensed by BP Solar to develop their Saturn cells, followed in the mid-1990s by a bifacial plated version licensed to Samsung. Since then, UNSW in collaboration with Suntech Power pioneered Light Induced Plating (LIP) for silicon solar cells, being subsequently awarded key patents for protecting the technology. This work included the development of commercial tools for large-scale manufacturing of LDSE cells with LIP contacts. This collaboration also pioneered the use of externally applied electric fields to plate p-type regions for bifacial implementations of the technology. Work is being carried out at UNSW using both light- and field-induced plating (LIP and FIP) which are both low-cost methods of metallising bifacial cells.

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Photovoltaic modules

At UNSW photovoltaic module research is focused on inventing and evaluating PV module structures that are highly efficient, low cost, easily manufacturable, and have the potential to be commercialised within 3-5 years.   This research encompasses;  advanced module materials, novel interconnection techniques (such as smart wire and multi busbar), bifaciality, PID mitigation, integration of advanced hydrogenation passivation processes, novel mounting techniques, and systems applications.

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Advanced Metrology

Professor Thorsten Trupke is the co-inventor of the photoluminescence (PL) imaging method for bricks, wafers, cells, and modules and is also one of the co-founders of BT Imaging. UNSW has a broad range of research capabilities in the area of PL, ranging from line scanning lifetime techniques for silicon bricks, lifetime imaging for as-cut wafers and contactless series resistance imaging of cells. Various spectral PL and EL measurement systems and unique measurement capabilities, such as a new PL inspection system for PV modules are also available. 

The PL group at UNSW also has extensive expertise in the application and analysis of correlation studies between PL metrics and cell efficiency data. In medium scale trials on state of the art industrial production lines, the PL imaging method has been utilised to monitor different parts of the PV value chain, such as ingot and wafer manufacturing, cell processing and finally module assembly. Even if under the umbrella of a vertically integrated company, the various processes are often isolated from each other, and the flow of information between the different production teams can be limited. As a result, the primary drivers of the final efficiency and yield of cells and modules and its correlation with the main material and process parameters are not well understood. Correlation of PL imaging metrics with final cell and module efficiency and yield can provide significant information for monitoring and control of the production line.

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Thin film photovoltaic technologies

Our school is also working on various thin film technologies which have a high potential to achieve efficiencies above 20%. In addition, these technologies are very suitable for integration in silicon-based tandem solar cells aiming at efficiencies well above 30%.

Perovskites

UNSW announced recent world record efficiencies for the largest certified perovskite cell at 12.1% on 16cm2 and 18% on 1.2 cm2, the largest certified cell at this efficiency. We have developed and will continue to develop deposition processes for large area perovskite devices to overcome the challenges associated with scaling. We have the capabilities for advanced cell design including interconnection design, optical analysis and optical management for best cell performance. UNSW also carries out fundamental studies of perovskite crystalline grains and grain boundaries to understand how grain characteristics affect electrical performance.  We continue to demonstrate cells with higher thermal stability, and we have identified the key degradation mechanisms. We are extending this work to cells incorporating perovskites with lower sensitivity to moisture and are also developing low-cost encapsulations for these devices. UNSW is also active in perovskite tandem solar cell research.

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CZTS

CZTS (Cu2ZnSnS4) thin film technologies provide a promising greener alternative with earth-abundance, non-toxicity and high stability than other thin film technologies. They also offer much wider flexibility in aesthetic designing for BIPV, choice of substrates and module sizes, as well as unlocking new applications through the use of flexible and light-weight substrates and Roll-To-Roll processing. With some key strategies developed and implemented, the UNSW CZTS team set a new world record for the energy conversion efficiency of 9.5% in 2016, which beats the previous record of 9.1% set by Japanese PV maker Toyota. Lately, the UNSW CZTS team set another new record and was able to achieve stable efficiencies of 11% (certified by NREL) through the engineering of the interfaces. While developing strategies to bring the efficiency towards and beyond 20%, we are interested in not only CZTS thin film solar cells but also tandem cells by stacking this CZTS thin film on Si cell for improving the overall performance.

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Advanced Photovoltaic Concepts

The Advanced PV Concepts group at UNSW is working on novel approaches with an aim to overcome the Shockley-Queisser (SQ) single bandgap efficiency limit. Currently, the group is working on the following technologies:

Hot carrier solar cells

With the efficiency limit over 65% at one sun (and over 85% at maximal concentration) and relatively simple structure, it is one of the most promising

Advanced PV concepts. As one of the most active research groups in the world, UNSW is working both on theoretical and experimental aspects. Having demonstrated the proof of concept of this technology recently, the current research is focused on investigating novel materials, structures and processes to improve the device performance.

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Quantum dot solar cells

Colloidal quantum dots (CQDs) are nano-sized semiconductor particles synthesized from solution-based chemical processes. They can be well dispersed in solvents to form “CQD inks”, which allow the fabrication of low-cost, flexible thin film solar cells through painting or spray-coating. In addition, due to the quantum size effect, the absorption ability of CQDs can be tuned across the entire solar spectrum through simple particle size control. This allows a CQD based solar cell to utilise all photons available from the sun, including the infrared range, which is not accessible to most other solar cell materials.



Our CQD research group focuses on the synthesis of CQDs and the fabrication of low-cost solar cells based on these materials. We are interested in CQDs made from a range of materials, including lead chalcogenides, perovskites and other non-toxic, earth abundant materials. In particular, our group reported the most efficient lead selenide based CQD solar cell and now still holds the record in the literature at 8.2%. We aim to advance the efficiency of low-cost solar cells based on CQDs, through particle surface engineering, optimisation of the device structure and simplification of the fabrication processes. We are also exploring hot carrier and multiple exciton generation effects in CQDs, which potentially allow CQD based devices to have efficiencies above the Schockley-Queisser limit for conventional single junction solar cells.

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Silicon quantum dot approaches

The group has significant expertise in the growth of deposition of thin film in-situ self-assembled solid state silicon quantum dots in various dielectric matrices. Band gap engineering is the primary motivation for this work with the potential to fabricate tandem cell devices made entirely from silicon and dielectrics, with recent proof of concept of this approach. Current work is directed at the investigation of the doping of these Si QDs at the atomic scale with atom probe tomography and TEM and application of Si QDs as passivating and carrier selective contact layers in silicon heterojunction solar cells.  

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Equivalent circuits for advanced concepts

This work uses solar cells of different band gaps as analogues of some of the advanced concept approaches. Low band gap GaSb cells, placed behind a bi-facial silicon cell, absorb long wavelength light and connected in series to multiply the voltage power a GaAs LED which illuminates the silicon cell as an analogue of up-conversion. Similar equivalent circuits are fabricated as analogues of down-conversion, intermediate band and in the future MEG and hot carrier cells. These equivalent circuits build on theory in the area and give some useful insights and also direct comparisons of these various approaches. Already the highest yet recorded efficiency for up-conversion at one sun has been reported.

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Photoelectrochemical cells

Photo-electrolysis of water has problems with both achieving sufficient carrier energy to overcome the redox potential of water and stability of photoelectrodes. The group uses a combined photo-cathode and photo-anode approach to overcome the energy problem in analgy to a tandem cell. A hematite photo-anode and silicon rich silicon carbide photo-cathode have demonstrated direct water splitting, but at low efficiency and limited stability. Improvements using combined zinc sulphide / silicon rich carbide photo-cathodes and up-conversion to boost current flow offer potential for much higher activities and solar to hydrogen efficiencies.

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Renewable Energy Integration, Policy and Markets

SPREE works with the Centre for Energy and Environmental Markets on interdisciplinary research on sustainable energy transitions, including modelling the technical and economic value and impacts of variable renewable energy, storage, demand response and distributed energy technologies in electricity markets and networks. We have work underway on cost reflective tariff design, electricity industry planning frameworks, fast frequency response markets and regulatory reform for new retail business models in the context of the renewable energy transition. We also have a range of work focussing on energy access in developing countries.

Building Integrated PV

Integrating PV systems into building façades and systems has several challenges from shading to aesthetics, to maintenance and reliability, to thermal management. The SPREE Systems Group investigates the use of Building integrated PV (BIPV) products as a low carbon retrofit solution for addressing thermally stressed high rise Commercial Office building facades and aims to develop cutting edge BIPV facade solutions for the major urban climates of Australia (temperate and sub-tropical). We aim to provide insights on the value that BIPV facades can provide for generating power during peak loads, reducing air conditioning needs without compromising natural daylighting and improving indoor environmental quality (IEQ). Our research objective is to develop innovative BIPV module designs that will maximise aesthetic appeal without significantly degrading electrical performance, minimise thermal and long term degradation and develop an innovative shading mitigation technology with broad applicability to PV systems.

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PV performance, prediction & modelling

Our research group has expertise in irradiance and PV modelling and performance analysis, including distributed energy data quality control and nowcasting, assessment of uncertainty in models, PV performance prediction based on spatial models and data, degradation analysis, and assessment of loss mechanisms in distributed PV systems. The group also has projects in energy meteorology and forecasting, including the integration of renewable energy supply, storage, and demand at the system level.

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Energy Efficiency

If Australia and the world are to reduce emissions of greenhouse gases, both renewable energy and more efficient use of that energy are required. Energy efficiency is often the cheapest, fastest, safest and simplest way to reduce emissions. Our research focusses on residential and commercial building design, energy management programs, building management systems, heating, ventilation and air conditioning (HVAC) systems, with particular emphasis on air handling and water pumping systems. We also focus on optimizing and predicting the thermal, solar, and lighting performance of commercial and residential buildings, using state of the art simulation software and techniques.  Life-cycle assessment is also used to ensure that long term energy, carbon and financial savings are achievable.  We also study the barriers to improving energy efficiency such as upfront cost, lack of information, regulation, and the cost of energy.

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Bio Energy

Building on a range of expertise in biomass in the school, there are now a number of small projects on bioenergy. The principal one of these is a third generation biofuel approach using algae grown in seawater with high concentrations of CO2 and illuminated by sunlight. Methanogenic bacteria and archaea break down the lipids in the algae to produce methane as a biofuel. In addition the growing coccolith shells of certain algal species absorb CO2 as calcium carbonate. Proof of concept of this approach as a means of combined biofuel production and CO2 sequestration has recently been achieved.

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