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Large greenhouse gas reductions are possible with a fully decarbonised grid and electric land transport. Additional electric load could pose a significant challenge to a grid with high levels of variable and non-dispatchable renewable energy sources. This scenario is not well-examined, nor is the use of pumped hydro energy storage for low-cost energy balancing. In this paper, we investigate the electrification of land transport within a photovoltaics and wind dominated 100% renewable electricity system. Only technologies that are deployed at scale and widely available globally are considered, namely photovoltaics, wind, battery electric vehicles, high voltage transmission, and pumped hydro. As a case study we present an hourly energy balance analysis of the Australian National Electricity Market with 100% renewables and 100% uptake of electric vehicles for land transport. The cost of the system is determined by occasional periods (days-weeks) of low renewable generation, and therefore only weakly dependent on the charging regime. The 40% increase in electricity demand due to electric land transport can be incorporated with a 4%–8% increase in the levelized cost of electricity. An exception occurs if most passenger vehicle charging occurs during the evening peak period, in which case the average price increases by about 18%.

Summary The difficulty of finding suitable sites for dams on rivers, including the associated environmental challenges, has caused many analysts to assume that pumped hydro energy storage has limited further opportunities to support variable renewable generation. Closed-loop, off-river pumped hydro energy storage overcomes many of the barriers. Small (square km) upper reservoirs are typically located in hilly country away from rivers, and water is circulated indefinitely between an upper and lower reservoir. GIS analysis of high resolution global digital elevation models was used to determine economically feasible closed-loop scheme locations outside protected and urban areas. This search identified 616,000 potential storage sites with an enormous combined storage potential of 23,000 TWh. This is two orders of magnitude more than required to support large fractions of renewable electricity, allowing flexible site selection. Importantly, the resource is widely distributed to effectively support large-scale solar and wind deployment for electrical grid decarbonization.

Titania (TiOx) is re-emerging to be a passivating material for the surfaces of high-efficiency crystalline silicon solar cells. Numerous sources in the literature suggest that the surface passivation and thermal stability of TiOx deteriorates with increasing film thickness when the TiOx film is thicker than a sufficient thickness. To circumvent this limitation, this study presents a novel process of Al-doped TiOx (TiOx:Al) film, which demonstrates the potential for improved thermal stability and surface passivation. Based on grazing incident X-ray diffraction and UV-Raman measurements, the incorporation of Al impurity in TiOx effectively restrains the crystal phase transformation of the amorphous TiOx layer during deposition. Furthermore, the TiOx:Al films provide better thermal robustness up to 350 °C, which makes it highly compatible with Si solar cell fabrication processes.

Solar photovoltaics (PVs) and wind constitute more than 60% of global annual net new capacity additions. Balancing an electricity system with 30–100% variable PV and wind is straightforward using off-the-shelf techniques comprising stronger interconnection over large areas to smooth out local weather, storage, demand management, and occasional spillage of renewable electricity. The overwhelming dominance of PV, wind, and hydroelectricity in new renewable energy deployment means that renewable electricity is tracking toward near equivalence with renewable energy. A global survey of off-river (closed-loop) pumped hydro energy storage sites identified 616 000 promising sites around the world with a combined storage capacity of 23 million GWh, which is two orders of magnitude more than required to support 100% global renewable electricity. This is significant because pumped hydro storage is the lowest cost storage method and is available off-the-shelf in large scale. Australia is deploying PV and wind at a rate of 250 W per year per capita, which is four to five times faster than in the European Union, the USA, Japan, and China. This is significant because it demonstrates that rapid deployment of PV and wind is feasible, with consequent rapid reductions in greenhouse gas emissions.

Rapid cost reductions have led to the widespread deployment of renewable technologies such as solar photovoltaics (PV) and wind globally. Additional storage is needed when the share of solar PV and wind in electricity production rises to 50-100%. Pumped hydro energy storage constitutes 97% of the global capacity of stored power and over 99% of stored energy and is the leading method of energy storage. Off-river pumped hydro energy storage options, strong interconnections over large areas, and demand management can support a highly renewable electricity system at a modest cost. East Asia has abundant wind, solar, and off-river pumped hydro energy resources. The identified pumped hydro energy storage potential is 100 times more than required to support 100% renewable energy in East Asia. Keywords: Photovoltaics, Wind energy, Pumped hydro energy storage, 100% renewable energy

Immeasurably low surface recombination of crystalline-silicon wafers is demonstrated with an oxide-nitride-oxide (ONO) corona charged dielectric stack. We detail experimental variations to each layer of the dielectric stack to establish a procedure which provides outstanding passivation properties on textured and planar silicon wafers. We demonstrate surface recombination velocities of

Good solar photovoltaic generation facilities are now the lowest cost source of electricity generation. However, solar generation is highly self-correlated and not well correlated to peak demand, leading to lower prices for solar generation relative to average value in markets. Energy storage provides the opportunity to shift generation from the middle of the day to meet evening and early morning peaks. Pumped hydro energy storage is the largest and cheapest source of electricity. Sites searching indicates that there are vastly more sites in the United States than could be needed for 100% renewable electricity. Levelised cost of storage for good pumped hydro sites is low. Continued installation of solar is enhancing the ‘duck curve’ effect, increasing the viability of bulk energy storage.

Solar photovoltaic (PV) energy is identified to be a vast energy source whose technical, environmental and economic potential far exceeds Indonesia’s present and future energy requirements. We estimate that electricity consumption in Indonesia could reach 9000 Terawatt-hours per year by 2050, which is 30 times larger than at present. Indonesia has abundant space to deploy enough solar PV to meet this requirement, including on rooftops, on inland reservoirs, on the Indonesian inland sea, on mining wasteland and in combination with agriculture.

Australia is installing PV and wind at 10 times the global per capita average rate and 3-5 times faster per capita than the USA, Japan, Europe or China. Australia’s National Electricity Market (NEM) and the state of South Australia reached {PV + wind} penetrations of 24% and 70% respectively and are tracking towards 40% and 100% in 2024. This represents a natural experiment in the cost of generation and balancing. The real cost of generation and balancing will become clearer as each year passes and the PV and wind fraction of electricity in Australia continues to increase. In response to rising PV and wind penetration, balancing investment in Australia is predominantly in off-river pumped hydro, transmission and batteries. The current (2021) and market futures (2024) price for electricity is in the range of US$35/MWh which includes both generation and balancing.

The GaAs/silicon tandem micro-concentrator module developed at the Australian National University can utilize diffuse and direct sunlight. The direct sunlight is concentrated onto narrow and long GaAs solar cells by long linear-focus non-imaging lenses. The concentrated direct sunlight of long wavelength that cannot be absorbed by the GaAs solar cell passes through the GaAs to the standard size silicon cell. Most of the diffuse sunlight escapes through the sides of the lenses, without being concentrated, towards the conventional silicon cell. The GaAs/silicon tandem micro-concentrator module design has a low profile and weight for use with one-axis tracking standard PV systems. The reliability and stability of GaAs and silicon solar cells fulfils the industry standards for commercial PV modules.

Gallium arsenide (GaAs) solar cells have shown demonstrated efficiencies of over 29% and are highly regarded in terms of stability, durability and performance. In order to make use of this excellent solar material while reducing inherent material costs, concentration of sunlight can be utilized. A linear microconcentrator has been designed to provide ∼7x concentrated sunlight to a narrow, long, GaAs cell, with a large area silicon cell underneath to collect the sub-bandgap light passing through the GaAs as well as any diffuse light that is not focused by the concentrator. This tandem linear microconcentrator module has demonstrated potential for efficiencies > 30%. In order to further optimize the design of the GaAs cell, a technique is being developed based on the Sliver method previously used with silicon. In order to adapt the Sliver process for GaAs applications it is critical to develop a technique for etching high aspect ratio grooves in GaAs. This work details the use of ICP/RIE to etch extremely deep, high aspect ratio grooves in GaAs up to a depth of $120 \mu \mathrm{m}$ with an aspect ratio of 9. The pathway for developing the etched GaAs into solar cells via ALD deposition of passivating contacts is also discussed.

The difficulty of finding suitable sites for dams on rivers, including the associated environmental challenges, has caused many analysts to assume that pumped hydro energy storage has limited further opportunities to support variable renewable generation. Closed loop, off-river pumped hydro energy storage overcomes many of the barriers. Small (square km) upper reservoirs are located in hilly country away from rivers, and water is circulated indefinitely between an upper and lower reservoir. GIS analysis of high resolution global digital elevation models has been used to determine economically feasible closed loop scheme locations outside protected and urban areas. This search identified 616,000 potential storage sites with an enormous combined storage potential of 23,000 TWh. This is two orders of magnitude more than required to support 100% renewable electricity, allowing flexible site selection. Importantly, the resource is widely distributed to effectively support large-scale solar and wind deployment for electrical grid decarbonisation

As silicon photovoltaic technology advances, charge carrier losses at the contacted interfaces of the silicon absorber are coming to dominate power conversion efficiency. The so-called passivated contact, which provides selective charge-carrier extraction while simultaneously reducing interface recombination, is thus of significant interest for next-generation silicon solar cells. However, achieving both low recombination and low resistance to charge carrier extraction has proven challenging. Here, we present a passivated contact technology based on polysilicon deposited using low pressure chemical vapour deposition (LPCVD) over an ultra-thin silicon dioxide layer, which achieves an excellent surface passivation with implied open-circuit voltage of 735 mV, a recombination prefactor below 1 fA cm−2 and contact resistivity below 1 mΩ cm2. Key to this technology is the deposition of an ultra-thin silicon dioxide interlayer under high temperature and low pressure condition, performed in-situ within a single process with the polysilicon deposition. Additionally, the passivating contact structure maintains its electronic properties at temperatures of up to 900 °C and is compatible with existing industrial processes. The presented work therefore represents a significant advancement in industrially-applicable passivated contact technology.

Silicon solar cells incorporating double-sided pyramidal texture are capable of superior light trapping over cells with front-side only texture. However, increased surface area, roughness and exposed crystal planes of textured surfaces not only causes increased recombination, but also makes cells susceptible to shunting through pinholes in the dielectric at the sharp peaks and valleys of the textured pyramids. A polyimide film as an insulating interlayer film is investigated to circumvent the tradeoff between improved light trapping, increased recombination and increased shunt paths. When applied at the rear of the interdigitated back contact silicon solar cell structure, the polyimide film provides an excellent electrical insulation (> 1000 MΩ of insulation resistance) and increases photocurrent (~ 1.1 mA/cm2) owing to an increased rear internal reflectance. The polyimide is also compatible with metal annealing of passivating dielectrics such as silicon nitride. Optical simulation and experimental results are combined in a 3D semiconductor simulation (Quokka) to quantify the possible gain of implementing the double-sided texture in high efficiency silicon solar cells.

Pumped hydro energy storage is capable of large-scale energy time shifting and a range of ancillary services, which can facilitate high levels of photovoltaics and wind integration in electricity grids. This study aims to develop a series of advanced Geographic Information System algorithms to locate prospective sites for off-river pumped hydro across a large land area such as a state or a country. Two typical types of sites, dry-gully and turkey’s nest, are modelled and a sequence of Geographic Information System-based procedures are developed for an automated site search. A case study is conducted for South Australia, where 168 dry-gully sites and 22 turkey’s nest sites have been identified with a total water storage capacity of 441 gigalitres, equivalent to 276 gigawatt-hours of energy storage. This demonstrates the site searching algorithms can work efficiently in the identification of off-river pumped hydro sites, allowing high-resolution assessments of pumped hydro energy storage to be quickly conducted on a broad scale. The sensitivity analysis shows the significant influences of maximum dam wall heights on the number of sites and the total storage capacity. It is noted that the novel models developed in this study are also applicable to the deployments of other types of pumped hydro such as the locations of dry-gully and turkey’s nest sites adjacent to existing water bodies, old mining pits and oceans.

Rapid increases in electricity consumption in Southeast Asia caused by rising living standards and population raise concerns about energy security, affordability and environmental sustainability. In this study, the role of short-term off-river energy storage (STORES) in supporting 100% renewable electricity in Southeast Asia is investigated. Large-scale integration of off-river, closed-loop pumped hydro storage is a new approach to providing system flexibility facilitating high penetration of variable renewable energy in electricity systems. The features of STORES include large storage potential, high technology maturity and a long service life. Energy generation, storage and transmission are co-optimised based on long-term, high-resolution chronological energy data. A comparative analysis is undertaken between the scenarios with and without an intercontinental Asia-Pacific Super Grid. The results show that, with support provided by STORES, the Southeast Asian electricity industry can achieve very high penetration (78%–97%) of domestic solar and wind energy resources. The levelised costs of electricity range from 55 to 115 U.S. dollars per megawatt-hour based on 2020 technology costs. In the Super Grid scenarios, the costs change by −4% to +7% while the storage requirements reduce by 50%–89%. Renewable energy supported by STORES can be a cost-effective solution for Southeast Asia's energy transition, delivering long-term, substantial environmental benefits.

In this paper, we conclude that Indonesia has vast potential for generating and balancing solar photovoltaic (PV) energy to meet future energy needs at a competitive cost. We systematically analyse renewable energy potential in Indonesia. Solar PV is identified to be an energy source whose technical, environmental and economic potential far exceeds Indonesia’s present and future energy requirements and is far larger than all other renewable energy resources combined. We estimate that electricity consumption in Indonesia could reach 9000 terawatt-hours per year by 2050, which is 30 times larger than at present. Indonesia has abundant space to deploy enough solar to meet this requirement, including on rooftops, inland reservoirs, mining wasteland, and in combination with agriculture. Importantly, Indonesia has a vast maritime area that almost never experiences strong winds or large waves that could host floating solar capable of generating &gt, 200,000 terawatt-hours per year. Indonesia also has far more off-river pumped hydro energy storage potential than required for balancing solar generation.

Accurate long-term wind speed data is important for understanding the role of offshore wind farms in future energy systems. Meteorological reanalyses, such as ERA5, are relied upon by the wind energy industry and researchers. Being unaffected by onshore topography and surface roughness, the historic generation of offshore wind farms can be accurately predicted using such weather reanalysis. In this work we present a new method for using ERA5 weather data to model long term (>40 year) hourly wind generation for individual offshore wind farms. The model is validated against 57 offshore wind farms in Europe, and reduces the root mean squared error in hourly and daily capacity factor predictions by 10% and 18% respectively when compared to the Renewables Ninja. Further, 40 years (from 1980 to 2019) of ERA5 hourly wind speeds within 200 km of the coast is made easily available for energy system research on our accompanying website (windtlas.xyz).

We investigate the light trapping in Si wafers that are textured with conventional random pyramids on their front surface and rounded random pyramids on their rear. It is well established that rounding the pyramids leads to better surface passivation, but whether or not it improves light trapping depends on the cell structure. In this paper, we apply ray tracing, spectrophotometry, and photoluminescence spectroscopy (PLS) to understand and quantify how rounding the rear pyramids might affect the light trapping in back-contact solar cells. We describe how rounding the pyramids leads to two competing optical effects: 1) reduced absorption in the rear films and 2) reduced scattering from the rear texture. The first effect improves light trapping whereas the latter degrades it. We show how the influence of each effect depends on wavelength and how they can be discerned (but not easily quantified) in reflectance curves. With PLS measurements, we conclude that for our sample structure and etch solution, the generation current is approximately constant for etch durations less than ∼60 s, and decreases significantly as the etch duration increases. Thus, by limiting the duration of the rounding etch, superior surface passivation can be attained without degrading the light trapping.

An hourly energy balance analysis is presented of the Australian National Electricity Market in a 100% renewable energy scenario, in which wind and photovoltaics (PV) provides about 90% of the annual electricity demand and existing hydroelectricity and biomass provides the balance. Heroic assumptions about future technology development are avoided by only including technology that is being deployed in large quantities (>10 Gigawatts per year), namely PV and wind. Additional energy storage and stronger interconnection between regions was found to be necessary for stability. Pumped hydro energy storage (PHES) constitutes 97% of worldwide electricity storage, and is adopted in this work. Many sites for closed loop PHES storage have been found in Australia. Distribution of PV and wind over 10–100 million hectares, utilising high voltage transmission, accesses different weather systems and reduces storage requirements (and overall cost). The additional cost of balancing renewable energy supply with demand on an hourly rather than annual basis is found to be modest: AU$25–30/MWh (US$19–23/MWh). Using 2016 prices prevailing in Australia, the levelised cost of renewable electricity (LCOE) with hourly balancing is estimated to be AU$93/MWh (US$70/MWh). LCOE is almost certain to decrease due to rapidly falling cost of wind and PV.

We analyze the potential benefits for behind-the-meter PV/battery systems of wholesale energy market participation in the Australian energy market. Using historic energy market price and demand data we show that PV / battery systems have the potential for significant financial benefit if operated so as to export during periods of peak wholesale pricing. The annual cost advantage over simple retail tariff optimization based operation, which is shared between electricity retailer and battery owner,varies considerably between regions and from year to year. No clear trends are evident over the last 10 years. We show that South Australia and Queensland are the most attractive markets for wholesale market participation. A 3 kW / 6 kWh behind-the-meter battery system, operated under reasonable and practical assumptions would have yielded around $80 per year on average over the most recent 5 years, or up to $150 per year if perfect look-ahead operationcould be achieved. The same battery system operating in Victoria or New South Wales, where price volatility is considerably less pronounced, would have yielded around $30 per year (up to only $40 per year with perfect look-ahead operation), while in Tasmania this would have been less than $10 per year. Weexplore a simple benefit sharing arrangement between battery owner and electricity retailer, using a pre-defined fixed price paid by retailers to battery owners for any exports occurring during periods of high markets prices. We find that a payment price (and accompanying export threshold) of $1.50 per kWh typically results in an even sharing of benefits. Finally, we speculate on the medium term outlook for battery system wholesale market participation, confirming the intuition that a high degree of participation is likely to result in the desired impact of ‘flattening’ the market and suppressing further market opportunity.

Rapidly increasing penetration of renewables, primarily wind and photovoltaics (PV), is causing a move away from fossil fuel in the Australian electric power industry. This study focuses on the South West Interconnected System in Western Australia. Several high (90% and 100%) renewables penetration scenarios have been modelled, comprising wind and PV supplemented with a small amount of biogas, and compared with a “like-for-like” fossil-fuel replacement scenario. Short-term off-river (closed cycle) pumped hydro energy storage (PHES) is utilised in some simulations as a large-scale conventional storage technology. The scenarios are examined by using a chronological dispatch model. An important feature of the modelling is that only technologies that have been already deployed on a large scale (>150 gigawatts) are utilised. This includes wind, PV and PHES. The modelling results demonstrate that 90–100% penetration by wind and PV electricity is compatible with a balanced grid. With the integration of off-river PHES, 90% renewables penetration is able to provide low-carbon electricity at competitive prices. Pumped hydro also facilitates a 100% renewables scenario which produces zero greenhouse gas emissions with attractive electricity prices. A sensitivity analysis shows the most important factors in the system cost are discount rate and wind turbine cost.

60% of global annual net new capacity comprise the addition of solar photovoltaics (PV) and wind. Indonesia has good solar resources by world standards, with low seasonal variation. There is also some wind energy potential. Solar PV is likely to be cheaper than new coal generation and can be rapidly deployed at every scale throughout Indonesia. Balancing an electricity system with large fractions of variable solar PV and wind can be managed with established techniques comprising stronger interconnection over large areas to average out local weather variations; storage; demand management; and occasional spillage of renewable electricity. Pumped hydro is by far the leading method of energy storage. Indonesia has 26,000 good pumped hydro sites with storage capacity of 821,000 Gigawatt-hours (GWh), which is about 1,000 times more than needed to support a 100% renewable Indonesian electricity system.

Australia has one of the highest per capita consumption of energy and emissions of greenhouse gases in the world. It is also the global leader in rapid per capita annual deployment of new solar and wind energy, which is causing the country's emissions to decline. Australia is located at low-moderate latitudes along with three quarters of the global population. These factors make the Australian experience globally significant. In this study, we model a fully decarbonised electricity system together with complete electrification of heating, transport and industry in Australia leading to an 80% reduction in greenhouse gas emissions. An energy supply-demand balance is simulated based on long-term (10 years), high-resolution (half-hourly) meteorological and energy demand data. A significant feature of this model is that short-term off-river energy storage and distributed energy storage are utilised to support the large-scale integration of variable solar and wind energy. The results show that high levels of energy reliability and affordability can be effectively achieved through a synergy of flexible energy sources; interconnection of electricity grids over large areas; response from demand-side participation; and mass energy storage. This strategy represents a rapid and generic pathway towards zero-carbon energy futures within the Sunbelt., Comment: Here is a summary of the study: https://www.dropbox.com/s/uvd90goh80y9eda/Zero-carbon%20Australia.pdf?dl=0

Surface texturing of a silicon solar cell is critical to provide surface antireflection and light trapping. The common texturing method based on KOH as an etchant with isopropyl alcohol (IPA) as a wetting agent suffers two disadvantages: introducing metal contamination and low repeatability. To circumvent the limitation of the KOH-IPA method, we develop a new texturing regime by substituting TMAH for KOH, and a commercial surfactant RENA monoTEX for IPA. This TMAH-monoTEX method shows advantages of non-metal contamination, high reproducibility, short process time and small random pyramids. IBC solar cells fabricated with the TMAH-monoTEX texture achieved an efficiency of 25% with Jsc of 42.9 mA/cm2, Voc of 719 mV and FF of 81.1%.

The need for storage in electricity systems is increasing because large amounts of variable solar and wind generation capacity are being deployed. About two thirds of net global annual power capacity additions are solar and wind. Pumped hydro energy storage (PHES) comprises about 96% of global storage power capacity and 99% of global storage energy volume. Batteries occupy most of the balance of the electricity storage market including utility, home and electric vehicle batteries. Batteries are rapidly falling in price and can compete with pumped hydro for short-term storage (minutes to hours). However, pumped hydro continues to be much cheaper for large-scale energy storage (several hours to weeks). Most existing pumped hydro storage is river-based in conjunction with hydroelectric generation. Water can be pumped from a lower to an upper reservoir during times of low demand and the stored energy can be recovered at a later time. In the future, the vast storage opportunities available in closed loop off-river pumped hydro systems will be utilized. In such systems water is cycled repeatedly between two closely spaced small reservoirs located away from a river. This review covers the technology, cost, environmental impacts and opportunities for PHES. The key motivations for this review are firstly that large amounts of variable wind and solar generators are being deployed; and secondly that there are vast opportunities for low-cost pumped hydro storage that do not require interference with rivers (with the associated environmental cost).

A tandem configuration of perovskite and silicon solar cells is a promising way to achieve high-efficiency solar energy conversion at low cost. Four-terminal tandems, in which each cell is connected independently, avoid the need for current matching between the top and bottom cells, giving greater design flexibility. In a four-terminal tandem, the perovskite top cell requires two transparent contacts. Through detailed analysis of electrical and optical power losses, we identify optimum contact parameters and outline directions for the development of future transparent contacts for tandem cells. A semitransparent perovskite cell is fabricated with steady-state efficiency exceeding 12% and broadband near infrared transmittance of >80% using optimized sputtered indium tin oxide front and rear contacts. Our semitransparent cell exhibits much less hysteresis than opaque reference cells. A four-terminal perovskite on silicon tandem efficiency of more than 20% is achieved, and we identify clear pathways to exceed the current single silicon cell record of 25.6%.

KGaA, Weinheim Mixed-dimensional perovskite solar cells combining 3D and 2D perovskites have recently attracted wide interest owing to improved device efficiency and stability. Yet, it remains unclear which method of combining 3D and 2D perovskites works best to obtain a mixed-dimensional system with the advantages of both types. To address this, different strategies of combining 2D perovskites with a 3D perovskite are investigated, namely surface coating and bulk incorporation. It is found that through surface coating with different aliphatic alkylammonium bulky cations, a Ruddlesden–Popper “quasi-2D” perovskite phase is formed on the surface of the 3D perovskite that passivates the surface defects and significantly improves the device performance. In contrast, incorporating those bulky cations into the bulk induces the formation of the pure 2D perovskite phase throughout the bulk of the 3D perovskite, which negatively affects the crystallinity and electronic structure of the 3D perovskite framework and reduces the device performance. Using the surface-coating strategy with n-butylammonium bromide to fabricate semitransparent perovskite cells and combining with silicon cells in four-terminal tandem configuration, 27.7% tandem efficiency with interdigitated back contact silicon bottom cells (size-unmatched) and 26.2% with passivated emitter with rear locally diffused silicon bottom cells is achieved in a 1 cm2 size-matched tandem.

Deep etched structures in GaAs have many applications in optoelectronics and MEMS devices. These applications often require an anisotropic etch profile with smooth sidewalls as well as a high etch rate and high aspect ratio. Developing an etch process that demonstrates high selectivity for the etch mask is critical as etch times for deep grooves can be protracted due to the effect of RIE lag. In this work, the authors describe etching deep, vertical grooves in GaAs using Inductively Coupled Plasma/Reactive Ion Etching. The effects of RF power, pressure, and gas composition on mask selectivity, etch rate, and anisotropy are discussed. Using a SiO2 etch mask and Cl2 as the main etchant gas, grooves with a vertical sidewall and depths of >120 μm (aspect ratio of 9) have been achieved.

This work presents the investigation of low pressure in-situ thermal oxidation as the interfacial oxide for n+ polysilicon-oxide passivated contact structure, achieving excellent surface passivation below 1 fA·cm-2 and contact resistivity below 1 mΩ·cm2. The results from the process optimisation are presented in detail, showing the importance of accurate control of oxidation conditions, and presenting the correlation to the electrical properties. Additionally, a method of fabricating contact resistivity structures from symmetrical photoconductance decay lifetime samples, and the extraction of the specific contact resistivity using 3D numerical simulation is presented.

The contact resistivity of evaporated Al on doped silicon is examined for a range of process conditions common to the fabrication of laboratory silicon solar cells. The effects of silicon surface preparation prior to evaporation, sintering temperature, the use of a shutter, and evaporation power are investigated. The presented evaporation conditions yielded the lowest published contact resistivity between Al- and phosphorus-doped Si over a large range of doping concentration. It is also demonstrated that a contact resistivity below 10−6 Ω·cm 2 can be achieved without sintering. Three-dimensional simulations are utilized to compare the obtained results for evaporated Al contacts with those for passivated contacts.

The interdigitated back contact (IBC) solar cells developed at the Australian National University have resulted in an independently confirmed (Fraunhofer Institut fur Solare Energiesysteme (ISE) CalLab) designated-area efficiency of 24.4 ± 0.7%, featuring short-circuit current density of 41.95 mA/cm2, open-circuit voltage of 703 mV and 82.7% fill factor. The cell, 2 × 2 cm2 in area, was fabricated on a 230 µm thick 1.5 Ω cm n-type Czochralski wafer, utilising plasma-enhanced chemical vapour deposition (CVD) SiNx front-surface passivation without front-surface diffusion, rear-side thermal oxide/low-pressure CVD Si3N4 passivation stack and evaporated aluminium contacts with a finger-to-finger pitch of 500 µm. This paper describes the design and fabrication of lab-scale high-efficiency IBC cells. Characterisation of optical and electronic properties of the best produced cell is made, with subsequent incorporation into 3D device modelling used to accurately quantify all losses. Loss analysis demonstrates that bulk and emitter recombination, bulk resistive and optical losses are dominant and suggests a clear route to efficiency values in excess of 25%. Additionally, laser processing is explored as a means to simplify the manufacture of IBC cells, with a confirmed efficiency value of 23.5% recorded for cells fabricated using damage-free deep UV laser ablation for contact formation. Meanwhile all-laser-doped cells, where every doping and patterning step is performed by lasers, are demonstrated with a preliminary result of 19.1% conversion efficiency recorded. Copyright © 2014 John Wiley & Sons, Ltd.

Metal assisted etching is a technique which can be used to etch high aspect ratio structures in silicon (Si) and has application in areas including solar cells, MEMS devices and the etching of through-silicon vias. The ability to etch in any direction on the Si wafer provides flexibility in terms of both processing and applications. Using gold as a catalyst, grooves were etched with metal assisted etching through a 650 μm-thick Si wafer with an aspect ratio of 22, independently of crystal orientation. Grooves were etched in a spiral pattern, allowing silicon segments up to 10 cm in length to be removed and unwound.

Interdigitated back-contact (IBC) solar cells developed in the past two years have efficiencies in the range 24.4%-25.6% As high as these efficiencies are, there are opportunities to increase them further by improving on the light trapping. Silicon solar cells incorporating double-sided pyramidal texture are capable of superior light trapping than cells with texture on just the front. One of the principle losses of double-sided pyramidal texture is the light that escapes after a second pass through the cell when the facet angles are the same on the front and rear. This contribution investigates how this loss might be reduced by changing the facet angle of the rear pyramids. A textured pyramid rounding is introduced to improve the light trapping. The reduction in surface recombination that rounding the facets introduces is also evaluated. With confocal microscopy, spectrophotometry and ray tracing, the rounding etch time required to yield the best light trapping is investigated. With photoconductance lifetime measurements, the surface recombination is found to continue to decrease as the rounding time increases. The spectrophotometry and ray tracing suggests that the double sided textured samples featuring rounded rear pyramids have superior light trapping to the sample with a planar rear surface. The high-efficiency potential of rounded textured pyramids in silicon solar cells is demonstrated by the fabrication of 24% efficient back-contact silicon solar cells.

A new dielectric totally internally reflecting concentrator (DTIRC) design has been developed for use with bifacial photovoltaic cells. The structure incorporates the bifacial cell standing vertically at the base of the structure, immersed in dielectric. DTIRC structures with single-sided photovoltaic receivers, like CPC structures, are designed using the paths of the edge rays to calculate the sidewalls. If these rays successfully hit the receiver then all rays at lower angles will also hit the receiver. In a vertical DTIRC structure, it is not just the edge rays that need to be taken into account in designing the structure. Around the bifacial receiver, rays at normal and close to normal incidence are the hardest to totally internally reflect onto the receiver. Once outside the area closest to the receiver, a modification of the maximum concentration method is used to design the remainder of the sidewalls. Ray tracing has been performed to confirm that the vertical DTIRC structure concentrates light as expected. The structure gives a lower concentration than a CPC with vertical bifacial receiver, however it is also a shorter structure with more uniform flux distribution over the receiver (leading to lower losses in the photovoltaic receiver).

We study a spectral-splitting perovskite-silicon tandem concept where the perovskite cell provides selective reflection of long wavelength light. Minimizing parasitic optical losses can lead to 2% efficiency gains, and tandem efficiencies of >26%.

A new technique for producing thin single-crystal silicon solar cells has been developed. The new technology allows for large decreases in silicon usage by a factor of 12 (including kerf losses) compared to conventional crystalline silicon wafer technologies. The new Sliver ® cell process uses a micromachining technique to form 60 μm-thick solar cells, fully processed while they are still supported by the silicon substrate at the edge of the wafer. The Sliver ® solar cells are capable of excellent performance due to their thickness and unique cell design with demonstrated efficiencies over 19.3% and open-circuit voltages of 683 mV. In addition, the cells are bifacial (accepts light from either sides) and very flexible. Several prototype modules have been fabricated using a new design approach that introduces a diffuse reflector to the rear of a bi-glass module. To save expensive silicon material, a significant gap is kept between cells. The light striking between cells is scattered from the rear reflector and is directed onto the rear surface of the bifacial Sliver ® cells. Module efficiency of 13% (AM1.5, 25C) has been demonstrated with a module presenting a 50% solar-cell coverage fraction, and 18.3% with a 100% Sliver ® cell coverage fraction.

Rubidium (Rb) is explored as an alternative cation to use in a novel multication method with the formamidinium/methylammonium/cesium (Cs) system to obtain 1.73 eV bangap perovskite cells with negligible hysteresis and steady state efficiency as high as 17.4%. The study shows the beneficial effect of Rb in improving the crystallinity and suppressing defect migration in the perovskite material. The light stability of the cells examined under continuous illumination of 12 h is improved upon the addition of Cs and Rb. After several cycles of 12 h light–dark, the cell retains 90% of its initial efficiency. In parallel, sputtered transparent conducting oxide thin films are developed to be used as both rear and front transparent contacts on quartz substrate with less than 5% parasitic absorption of near infrared wavelengths. Using these developments, semi-transparent perovskite cells are fabricated with steady state efficiency of up to 16.0% and excellent average transparency of ≈84% between 720 and 1100 nm. In a tandem configuration using a 23.9% silicon cell, 26.4% efficiency (10.4% from the silicon cell) in a mechanically stacked tandem configuration is demonstrated which is very close to the current record for a single junction silicon cell of 26.6%.

A procedure to quantify the optical loss mechanisms in back-contact solar cells is presented. It incorporates recent developments in optical simulation that yield rapid and precise results. The procedure includes spectrophotometry, ellipsometry, quantum efficiency measurements, ray tracing, and the thin-film matrix method. The paper shows how experiments and simulation can be combined to quantify reflection from the front surface, absorption in the antireflection coatings, non-ideal light trapping, and free-carrier absorption—all in terms of a ‘lost generation current’. The procedure is demonstrated on a back-contact solar cell with single-layer and double-layer antireflection coatings. It is extendable to other cell structures.

A significant reduction in contact resistance of palladium/silicon contacts was realised by the use of a thin intermediate gallium layer. The contact resistance of the palladium/gallium/silicon contact was found to be similar to aluminium/silicon contacts on 0.5 Ω cm silicon. Solar cells processed on 1 Ω cm substrates with this structure demonstrated better contact properties than conventional aluminium/silicon contacts. The improved characteristics are believed to be a result of gallium/silicon alloying at low temperature (400°C). The palladium layer is critical as aluminium/gallium/silicon layers show dramatically increased contact resistance. The palladium silicide may interact with the aluminium layer to form a stable ternary compound, preventing aluminium from penetrating deeper into the silicon. Copyright © 2001 John Wiley & Sons, Ltd.