The emergence of semiconductor nanocrystals as the building blocks of nanotechnology has opened up new ways to utilize them in next generation solar cells. This paper focuses on the recent developments in the utilization of semiconductor quantum dots for light energy conversion. Three major ways to utilize semiconductor dots in solar cell include (i) metal−semiconductor or Schottky junction photovoltaic cell (ii) polymer−semiconductor hybrid solar cell, and (iii) quantum dot sensitized solar cell. Modulation of band energies through size control offers new ways to control photoresponse and photoconversion efficiency of the solar cell. Various strategies to maximize photoinduced charge separation and electron transfer processes for improving the overall efficiency of light energy conversion are discussed. Capture and transport of charge carriers within the semiconductor nanocrystal network to achieve efficient charge separation at the electrode surface remains a major challenge. Directing the future resear...

http://wiki.phy.queensu.ca/shughes/images/d/d1/Quantum_Dot_Solar_Cells._Semiconductor_Nanocrystals_as_Light_Harvesters.pdf

Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters

Annual Energy Outlook

Microgrids are now emerging from lab benches and pilot demonstration sites into commercial markets, driven by technological improvements, falling costs, a proven track record, and growing recognition of their benefits. They are being used to improve reliability and resilience of electrical grids, to manage the addition of distributed clean energy resources like wind and solar photovoltaic (PV) generation to reduce fossil fuel emissions, and to provide electricity in areas not served by centralized electrical infrastructure. This review article (1) explains what a microgrid is, and (2) provides a multi-disciplinary portrait of today's microgrid drivers, real-world applications, challenges, and future prospects.

/pdf/microgrids-a-review-of-technologies-key-drivers-and-3wo8bifusj.pdf

Microgrids: A review of technologies, key drivers, and outstanding issues

Single-nanowire solar cells were created by forming rectifying junctions in electrically contacted vapor-liquid-solid-grown Si nanowires. The nanowires had diameters in the range of 200 nm to 1.5 microm. Dark and light current-voltage measurements were made under simulated Air Mass 1.5 global illumination. Photovoltaic spectral response measurements were also performed. Scanning photocurrent microscopy indicated that the Si nanowire devices had minority carrier diffusion lengths of approximately 2 microm. Assuming bulk-dominated recombination, this value corresponds to a minimum carrier lifetime of approximately 15 ns, or assuming surface-dominated recombination, to a maximum surface recombination velocity of approximately 1350 cm s(-1). The methods described herein comprise a valuable platform for measuring the properties of semiconductor nanowires, and are expected to be instrumental when designing an efficient macroscopic solar cell based on arrays of such nanostructures.

Photovoltaic Measurements in Single-Nanowire Silicon Solar Cells

As China’s rapid urbanization continues and urban dwellers become more affluent, energy use in buildings is expected to grow. To understand how this growth can be slowed, we explore four scenarios for Chinese buildings, ranging from a high-energy-demand scenario with no new energy policies to lowest energy demand under a techno-economic-potential scenario that assumes full deployment of cost-effective efficient and renewable technologies by 2050. We show that, in the high energy demand scenario, building energy demand has an average annual growth rate of about 2.8%, with slower growth rates in the other three scenarios. In all scenarios, CO2 emissions grow slower than energy, with building CO2 peaking around 2045 in the high energy demand scenario, and as early as 2030 in the techno-economic-potential scenario. We show that although various technological solutions, systems and practices can be very effective in minimizing building energy use, rigorous policies are needed to overcome multiple implementation barriers.

/pdf/scenarios-of-energy-efficiency-and-co-2-emissions-reduction-20voajbhue.pdf

Scenarios of energy efficiency and CO 2 emissions reduction potential in the buildings sector in China to year 2050

The mobility−lifetime products (μτ) for electrons and holes in CdS nanowires were quantitatively determined by scanning photocurrent microscopy of devices with ohmic contacts. Ohmic contacts were fabricated by ion bombardment of the contact regions. By analyzing the spatial profiles of the local photoconductivity maps, we determined that electron transport (μeτe ≈ 5 × 10-7 cm2/V) was more efficient than hole transport (μhτh ≈ 10-7 cm2/V). The results demonstrate that photocurrent mapping can provide quantitative insight into intrinsic carrier transport properties of semiconductor nanostructures.

Quantitative Measurement of the Electron and Hole Mobility−Lifetime Products in Semiconductor Nanowires

Three types of two-terminal CdS nanowire devices with distinct current versus voltage characteristics were fabricated by forming Schottky and/or Ohmic contacts in a controlled manner. Argon ion bombardment of CdS nanowires increased the carrier concentration allowing the formation of Ohmic Ti–CdS contacts. Scanning photocurrent microscopy (SPCM) was used to explore the influence of the contacts on the spatially resolved photoresponse in two-terminal devices and to analyze charge carrier transport processes. Modeling of the spatial profiles of the local photocurrent images enabled the quantitative extraction of electron and hole mobility-lifetime products in Ohmic devices and the hole mobility-lifetime product in Schottky devices. Analysis of the evolution of SPCM images with bias suggests that the electric field is localized to the optical generation region in the Ohmic devices and localized beneath the contacts in the Schottky devices.

Local photocurrent mapping as a probe of contact effects and charge carrier transport in semiconductor nanowire devices

Lessons from international experience for China's microgrid demonstration program

More than 130 countries have targets for increasing their share of renewable or nonfossil energy ( 1 ). These shares and targets are often reported without clear articulation of which energy accounting method was used to convert nonfossil electricity into units that allow comparison with other energy sources ( 2 – 4 ). Three commonly used conversion methods are well documented by organizations dealing in energy statistics, but often, the method is not clearly stated when countries translate national targets into international pledges or when organizations track and compare targets across nations. China—the world's largest energy producer, energy consumer, and emitter of energy-related carbon dioxide (CO2)—uses a distinct fourth method that is unique, not well documented in the literature, and not transparent in policy documents. A single, standardized, and transparent methodology for any targets that are pledged as part of an international agreement is essential.

https://science.sciencemag.org/content/sci/350/6264/1034.full.pdf

Understanding China's non–fossil energy targets

Addressing the effectiveness of industrial energy efficiency incentives in overcoming investment barriers in China John Romankiewicz, Bo Shen, Hongyou Lu, and Lynn Price China Energy Group Environmental Energy Technologies Division Lawrence Berkeley National Laboratory Post-print version of proceedings of the European Council for an Energy Efficient Economy’s 2012 Industrial Summer Study, held in Arnhem, the Netherlands, on September 11-14, 2012. October 2012 This work was supported by the China Sustainable Energy Program (CSEP) of the Energy Foundation, Azure International, and Dow Chemical Company (through a charitable contribution) through the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

/pdf/addressing-the-effectiveness-of-industrial-energy-efficiency-dl086of6gz.pdf

John Romankiewicz

Papers

Quantitative Measurement of the Electron and Hole Mobility−Lifetime Products in Semiconductor Nanowires

Local photocurrent mapping as a probe of contact effects and charge carrier transport in semiconductor nanowire devices

Lessons from international experience for China's microgrid demonstration program

Understanding China's non–fossil energy targets

Addressing the effectiveness of industrial energy efficiency incentives in overcoming investment barriers in China