Vernie Everett

A novel low-cost, high-efficiency micromachined silicon solar cell

This letter presents a new process for the fabrication of solar cells and modules from single crystal silicon wafers with substantially reduced silicon consumption and processing effort compared to conventional wafer-based cells. The technique of narrow trench etching in an alkaline solution is used to create a series of thin silicon strips extending vertically through the wafer. By turning the silicon strips on their side, a large increase in surface area is achieved. Individual cells fabricated using the new process have reached efficiencies up to 18.5% while a 575 cm/sup 2/ module incorporating a rear reflector and a cell surface coverage of 50% has displayed an efficiency of 12.3% under standard rating conditions. The technique has the potential to reduce silicon consumption by a factor of 10 compared to standard wafer-based silicon solar cells and, therefore, to dramatically reduce the dependence to the expensive silicon feedstock.

Sliver solar cells: high efficiency, low cost PV technology

Sliver cells are thin, single-crystal silicon solar cells fabricated using standard fabrication technology. Sliver modules, composed of several thousand individual Sliver cells, can be efficient, low-cost, bifacial, transparent, flexible, shadow tolerant, and lightweight. Compared with current PV technology, mature Sliver technology will need 10% of the pure silicon and fewer than 5% of the wafer starts per MW of factory output. This paper deals with two distinct challenges related to Sliver cell and Sliver module production: providing a mature and robust Sliver cell fabrication method which produces a high yield of highly efficient Sliver cells, and which is suitable for transfer to industry; and, handling, electrically interconnecting, and encapsulating billions of sliver cells at low cost. Sliver cells with efficiencies of 20% have been fabricated at ANU using a reliable, optimised processing sequence, while low-cost encapsulation methods have been demonstrated using a submodule technique.

Sliver Cells - A Complete Photovoltaic Solution

Sliver technology was invented and developed at the Australian National University, with support from the Australian company Origin Energy. The Sliver process uses standard materials and techniques in novel ways to create thin single crystalline solar cells with superior performance and reduced cost. Sliver cells are made from very thin single crystalline silicon, and are highly efficient. Sliver technology offers reductions in silicon consumption by a factor of 10-15 and reductions in wafer throughput per Megawatt by a factor of 20-50. This paper examines the economic potential of Sliver cells. We show that, with careful engineering, a reduction in the cost of PV modules of up to three quarters is possible in the medium term, without the need for any breakthroughs. Sliver technology, with its low cost and multiple attributes, could be a long-term solution for photovoltaics

A 20-sun hybrid PV-Thermal linear micro-concentrator system for urban rooftop applications

A unique, linear, low-concentration, hybrid ‘micro-concentrator’ (MCT) system concept has been developed specifically for urban rooftop environments. The light-weight, low-profile form factor satisfies aesthetic demands for general rooftop solar technologies, and is a marked departure from conventional linear concentrator systems. Valuable thermal energy, normally of nuisance value only, and usually wasted by conventional CPV, is extracted via a heat transfer fluid. The recovered thermal energy can be used for applications ranging from domestic hot water through to space heating, ventilation, and air conditioning (HVAC), and process heat. The system can be modularly configured for hybrid concentrating PV-Thermal (CPV-T) or thermal-only operation to meet specific customer demands. At a 20x concentration ratio, system output of 500 Wpe and 2 kWpt is expected, for a combined system efficiency of up to 75%. The MCT is constructed from mature, proven technologies and industry-standard processes. An installed system cost of less than US

Numerical analysis of direct liquid-immersed solar cell cooling of a linear concentrating photovoltaic receiver

2/Wpe is targeted, and commercial availability is expected to commence in 2011.

Miniature silicon solar cells for High Efficiency Tandem Cells

Direct liquid immersion cooling of concentrator solar cells is proposed as a solution for receiver thermal management of concentrating photovoltaic (CPV) and hybrid concentrating photovoltaic thermal (CPV-T) systems. A novel receiver incorporating direct liquid-immersed cell cooling has been developed for linear trough CPV and CPV-T systems at ANU. Several potential working fluids have undergone preliminary investigation as candidate immersion liquids in the novel receiver. De-ionised (DI) water has been used as the working fluid in this study. The flow distribution and concentrator solar cell temperature profiles from three-dimensional numerical simulations are presented. The optical concentration ratio, the fluid inlet velocity and fluid flow characteristics, and the inlet fluid temperature have a decisive influence on the concentrator solar cell operating temperature.

Results from the first ANU-chromasun CPV-T microconcentrator prototype in Canberra

In this paper, a discussion is made of the design of silicon cells to be used in a six-junction tandem solar cell structure as part of the Very High Efficiency Solar Cell (VHESC) program. Minority carrier recombination at surfaces and in the volume, internal quantum efficiency, resistance losses, free carrier parasitic absorption, optical reflection, light trapping, and light absorption must be traded off against each other. Modelling was used to analyse the various parameters and produce estimates of short circuit current, fill factor and open-circuit voltage of the cell. In addition, quasi-steady-state photoconductance measurements to analyse carrier recombination and emitter saturation current (Joe) as well as to predict the open-circuit voltage of solar cell is presented. For metallisation of such small solar cells, alternate methods of making contact such as light-induced plating and electrolyte plating in addition to evaporating metal on the contacts were explored and employed. Numerical resistive loss modelling was made to calculate the optimum metal thickness achieved by light-induced and electroplating to minimise resistive losses. Experiments were conducted to determine the proper plating rate by light-induced and electrolyte plating. Cells were fabricated by standard silicon processing techniques followed by testing of IV curves using current-voltage flash-tester to achieve the target efficiency.

Design, characterization and fabrication of silicon solar cells for ≫50% efficient 6-junction tandem solar cells

A first prototype of the hybrid CPV-T ANU-Chromasun micro-concentrator (MCT) has been installed at The Australian National University (ANU), Canberra, Australia. The results of electrical and thermal performance of the MCT system, including instantaneous and full-day monitoring, show that the combined efficiency of the system can exceed 70%. Over the span of a day, the average electrical efficiency was 8% and the average thermal efficiency was 60%.

Towards a Simplified 20% Efficient Sliver Cell

A major objective for photovoltaic conversion is to develop high efficiency solar cells. Many approaches are under investigation - Multiple Junction Solar Cell, Multiple Spectrum Solar Cell, Multiple Absorption Path Solar Cell, Multiple Energy Solar Cell, and Multiple Temperature Solar Cells [1]. The Multiple Junction Solar Cell approach based on a six-junction tandem solar cell has been adopted to achieve conversion efficiency of greater than 50% in the VHESC program sponsored by DARPA [2]. In six-junction tandem solar cells, individual solar cells are stacked on one another and each solar cell absorbs the best-matched slice of the solar spectrum. Silicon is one of the cells in the tandem stacks, and absorbs photon energy of 1.42 – 1.1 eV. The role of the silicon cell is to convert 7% of the light incident on the tandem stack into electricity. Other cells in the stack contribute the balance of the electricity. Key design parameters for the silicon cells are that it should have dimensions of 2.5 × 8 mm2 and it needs to transfer light with energy of less than 1.1ev to the underlying solar cells. In this paper, discussion is made of the design of the silicon cell. Minority carrier recombination at surfaces and in the volume, internal quantum efficiency, resistance losses, free carrier parasitic absorption, optical reflection, light trapping, and light absorption must be traded off against each other. PC1D modeling is used to analyze the various parameters and produce estimates of short circuit current, fill factor and open-circuit voltage of the cell [3]. In addition, characterization of solar cell by photoconductance measurement to analyze carrier recombination and emitter saturation current as well as to predict the open-circuit voltage of solar cell [4, 5] is presented. Discussion of cell fabrication process followed by I–V testing is presented. Completed solar cells were tested in ANU using an in-house fabricated current-voltage flash tester [6] under AM1.5D.

Investigation of the Temperature Dependence of the Optical Properties of Thermal Transfer Fluids for Hybrid CPV-T Systems

Sliver technology, first developed at the ANU, offers large reductions in silicon consumption and wafer throughput per MW. However, sliver technology requires more processing steps than conventional silicon solar cell fabrication, and thus fabrication represents a larger cost per wafer. This additional cost is easily justified because sliver cells are highly efficient and also the module area producible per wafer is far greater than for conventional technologies. Current research at the ANU is aimed at delivering a simplified processing sequence capable of producing sliver cells with a reduced manufacturing cost and with better performance than the originally developed fabrication process. With the simplified process it should be possible to reliably manufacture > 20% efficient cells with a high yield