Joshua M. Pearce

Analytical model for the optical functions of amorphous semiconductors from the near-infrared to ultraviolet: Applications in thin film photovoltaics

We have developed a Kramers–Kronig consistent analytical expression to fit the measured optical functions of hydrogenated amorphous silicon (a-Si:H) based alloys, i.e., the real and imaginary parts of the dielectric function (e1,e2) (or the index of refraction n and absorption coefficient α) versus photon energy E for the alloys. The alloys of interest include amorphous silicon–germanium (a-Si1−xGex:H) and silicon–carbon (a-Si1−xCx:H), with band gaps ranging continuously from ∼1.30 to 1.95 eV. The analytical expression incorporates the minimum number of physically meaningful, E independent parameters required to fit (e1,e2) versus E. The fit is performed simultaneously throughout the following three regions: (i) the below-band gap (or Urbach tail) region where α increases exponentially with E, (ii) the near-band gap region where transitions are assumed to occur between parabolic bands with constant dipole matrix element, and (iii) the above-band gap region where (e1,e2) can be simulated assuming a single ...

Evolution of microstructure and phase in amorphous, protocrystalline, and microcrystalline silicon studied by real time spectroscopic ellipsometry

Real time spectroscopic ellipsometry has been applied to develop deposition phase diagrams that can guide the fabrication of hydrogenated silicon (Si:H) thin films at low temperatures (<300°C) for highest performance electronic devices such as solar cells. The simplest phase diagrams incorporate a single transition from the amorphous growth regime to the mixed-phase (amorphous+microcrystalline) growth regime versus accumulated film thickness [the a→(a+μc) transition]. These phase diagrams have shown that optimization of amorphous silicon (a-Si:H) intrinsic layers by RF plasma-enhanced chemical vapor deposition (PECVD) at low rates is achieved using the maximum possible flow ratio of H2 to SiH4 that can be sustained while avoiding the a→(a+μc) transition. More recent studies have suggested that a similar strategy is appropriate for optimization of p-type Si:H thin films. The simple phase diagrams can be extended to include in addition the thickness at which a roughening transition is detected in the amorphous film growth regime. It is proposed that optimization of a-Si:H in higher rate RF PECVD processes further requires the maximum possible thickness onset for this roughening transition.

Building Research Equipment with Free, Open-Source Hardware

A rapidly increasing selection of laboratory equipment can be fabricated with open-source three-dimensional printers at low cost. Most experimental research projects are executed with a combination of purchased hardware equipment, which may be modified in the laboratory and custom single-built equipment fabricated inhouse. However, the computer software that helps design and execute experiments and analyze data has an additional source: It can also be free and open-source software (FOSS) (1). FOSS has the advantage that the code is openly available for modification and is also often free of charge. In the past, customizing software has been much easier than custom-building equipment, which often can be quite costly because fabrication requires the skills of machinists, glassblowers, technicians, or outside suppliers. However, the open-source paradigm is now enabling creation of open-source scientific hardware by combining three-dimensional (3D) printing with open-source microcontrollers running on FOSS. These developments are illustrated below by several examples of equipment fabrication that can better meet particular specifications at substantially lower overall costs.

Quantifying Rooftop Solar Photovoltaic Potential for Regional Renewable Energy Policy

Solar photovoltaic (PV) technology has matured to become a technically viable large-scale source of sustainable energy. Understanding the rooftop PV potential is critical for utility planning, accommodating grid capacity, deploying financing schemes and formulating future adaptive energy policies. This paper merges the capabilities of geographic information systems and object-based image recognition to determine the available rooftop area for PV deployment in an example large-scale region in south eastern Ontario. An innovative five-step procedure has been developed for estimating total rooftop PV potential which involves geographical division of the region; sampling using the Feature Analyst extraction software; extrapolation using roof area-population relationships; reduction for shading, other uses and orientation; and conversion to power and energy outputs. A relationship across the region was found between roof area and population of 70.0 m2/capita ± 6.2%. For this region with appropriate roof tops covered with commercial solar cells the potential PV peak power output is 5.74 GW (157% of the region’s peak power demands) and the potential annual energy production is 6909 Gwh (5% of Ontario’s total annual demand). This suggests that 30% of Ontario’s demand can be met with province-wide rooftop PV deployment. This new understanding of roof area distribution and potential PV outputs has an immense significance to energy policy formulation in Ontario and the methodology developed here is transferable in other regions to assist in solar PV deployment.

Photovoltaics - A Path to Sustainable Futures

As both population and energy use per capita increase, modern society is approaching physical limits to its continued fossil fuel consumption. The immediate limits are set by the planet’s ability to adapt to a changing atmospheric chemical composition, not the availability of resources. In order for a future society to be sustainable while operating at or above our current standard of living a shift away from carbon based energy sources must occur. An overview of the current state of active solar (photovoltaic) energy technology is provided here to outline a partial solution for the environmental problems caused by accelerating global energy expenditure. The technical, social, and economic benefits and limitations of photovoltaic technologies to provide electricity in both off-grid and on-grid applications is critically analyzed in the context of this shift in energy sources. It is shown that photovoltaic electrical production is a technologically feasible, economically viable, environmentally benign, sustainable, and socially equitable solution to society’s future energy requirements.

Open-Source 3D-Printable Optics Equipment

Just as the power of the open-source design paradigm has driven down the cost of software to the point that it is accessible to most people, the rise of open-source hardware is poised to drive down the cost of doing experimental science to expand access to everyone. To assist in this aim, this paper introduces a library of open-source 3-D-printable optics components. This library operates as a flexible, low-cost public-domain tool set for developing both research and teaching optics hardware. First, the use of parametric open-source designs using an open-source computer aided design package is described to customize the optics hardware for any application. Second, details are provided on the use of open-source 3-D printers (additive layer manufacturing) to fabricate the primary mechanical components, which are then combined to construct complex optics-related devices. Third, the use of the open-source electronics prototyping platform are illustrated as control for optical experimental apparatuses. This study demonstrates an open-source optical library, which significantly reduces the costs associated with much optical equipment, while also enabling relatively easily adapted customizable designs. The cost reductions in general are over 97%, with some components representing only 1% of the current commercial investment for optical products of similar function. The results of this study make its clear that this method of scientific hardware development enables a much broader audience to participate in optical experimentation both as research and teaching platforms than previous proprietary methods.

Distributed recycling of waste polymer into RepRap feedstock

– A low‐cost, open source, self‐replicating rapid prototyper (RepRap) has been developed, which greatly expands the potential user base of rapid prototypers. The operating cost of the RepRap can be further reduced using waste polymers as feedstock. Centralized recycling of polymers is often uneconomic and energy intensive due to transportation embodied energy. The purpose of this paper is to provide a proof of concept for high‐value recycling of waste polymers at distributed creation sites., – Previous designs of waste plastic extruders (also known as RecycleBots) were evaluated using a weighted evaluation matrix. An updated design was completed and the description and analysis of the design is presented including component summary, testing procedures, a basic life cycle analysis and extrusion results. The filament was tested for consistency of density and diameter while quantifying electricity consumption., – Filament was successfully extruded at an average rate of 90 mm/min and used to print parts. The filament averaged 2.805 mm diameter with 87 per cent of samples between 2.540 mm and 3.081 mm. The average mass was 0.564 g/100 mm length. Energy use was 0.06 kWh/m., – The success of the RecycleBot further reduces RepRap operating costs, which enables distributed in‐home, value added, plastic recycling. This has implications for municipal waste management programs, as in‐home recycling could reduce cost and greenhouse gas emissions associated with waste collection and transportation, as well as the environmental impact of manufacturing custom plastic parts., – This paper reports on the first technical evaluation of a feedstock filament for the RepRap from waste plastic material made in a distributed recycling device.

Producer Responsibility and Recycling Solar Photovoltaic Modules

Rapid expansion of the solar photovoltaic (PV) industry is quickly causing solar to play a growing importance in the energy mix of the world. Over the full life cycle, although to a smaller degree than traditional energy sources, PV also creates solid waste. This paper examines the potential need for PV recycling policies by analyzing existing recycling protocols for the five major types of commercialized PV materials. The amount of recoverable semiconductor material and glass in a 1 m2 area solar module for the five types of cells is quantified both physically and the profit potential of recycling is determined. The cost of landfill disposal of the whole solar module, including the glass and semiconductor was also determined for each type of solar module. It was found that the economic motivation to recycle most PV modules is unfavorable without appropriate policies. Results are discussed on the need to regulate for appropriate energy and environmental policy in the PV manufacturing industry particularly for PV containing hazardous materials. The results demonstrate the need to encourage producer responsibility not only in the PV manufacturing sector, but also the entire energy industry.

The Case for Open Source Appropriate Technology

Much of the widespread poverty, environmental desecration, and waste of human life seen around the globe could be prevented by known (to humanity as a whole) technologies, many of which are simply not available to those that need it. This lack of access to critical information for sustainable development is directly responsible for a morally and ethically unacceptable level of human suffering and death. A solution to this general problem is the concept of open source appropriate technology or OSAT, which refers to technologies that provide for sustainable development while being designed in the same fashion as free and open source software. OSAT is made up of technologies that are easily and economically utilized from readily available resources by local communities to meet their needs and must meet the boundary conditions set by environmental, cultural, economic, and educational resource constraints of the local community. This paper explores both the open source and appropriate technology aspects of OSAT to create a paradigm, in which anyone can both learn how to make and use needed technologies free of intellectual property concerns. At the same time, anyone can also add to the collective open source knowledge ecosystem or knowledge commons by contributing ideas, designs, observations, experimental data, deployment logs, etc. It is argued that if OSAT continues to grow and takes hold globally creating a vibrant virtual community to share technology plans and experiences, a new technological revolution built on a dispersed network of innovators working together to create a just sustainable world is possible.

Exchanging Ohmic Losses in Metamaterial Absorbers with Useful Optical Absorption for Photovoltaics

Using metamaterial absorbers, we have shown that metallic layers in the absorbers do not necessarily constitute undesired resistive heating problem for photovoltaics. Tailoring the geometric skin depth of metals and employing the natural bulk absorbance characteristics of the semiconductors in those absorbers can enable the exchange of undesired resistive losses with the useful optical absorbance in the active semiconductors. Thus, Ohmic loss dominated metamaterial absorbers can be converted into photovoltaic near-perfect absorbers with the advantage of harvesting the full potential of light management offered by the metamaterial absorbers. Based on experimental permittivity data for indium gallium nitride, we have shown that between 75%–95% absorbance can be achieved in the semiconductor layers of the converted metamaterial absorbers. Besides other metamaterial and plasmonic devices, our results may also apply to photodectors and other metal or semiconductor based optical devices where resistive losses and power consumption are important pertaining to the device performance.