Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Over the last 12 months, we have witnessed an unexpected breakthrough and rapid evolution in the field of emerging photovoltaics, with the realization of highly efficient solid-state hybrid solar cells based on organometal trihalide perovskite absorbers. In this Perspective, the steps that have led to this discovery are discussed, and the future of this rapidly advancing concept have been considered. It is likely that the next few years of solar research will advance this technology to the very highest efficiencies while retaining the very lowest cost and embodied energy. Provided that the stability of the perovskite-based technology can be proven, we will witness the emergence of a contender for ultimately low-cost solar power.

Perovskites: The Emergence of a New Era for Low-Cost, High-Efficiency Solar Cells

In this Progress Report we provide an update on recent developments in inkjet printing technology and its applications, which include organic thin-film transistors, light-emitting diodes, solar cells, conductive structures, memory devices, sensors, and biological/pharmaceutical tasks. Various classes of materials and device types are in turn examined and an opinion is offered about the nature of the progress that has been achieved.

Inkjet Printing—Process and Its Applications

We report a new record total-area efficiency of 19·9% for CuInGaSe2-based thin-film solar cells. Improved performance is due to higher fill factor. The device was made by three-stage co-evaporation with a modified surface termination. Growth conditions, device analysis, and basic film characterization are presented. Published in 2008 by John Wiley & Sons, Ltd.

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19·9%‐efficient ZnO/CdS/CuInGaSe2 solar cell with 81·2% fill factor

In this contribution, we present a new certified world record efficiency of 20.1 and 20.3% for Cu(In,Ga)Se2 thin-film solar cells. We analyse the characteristics of solar cells on such a performance level and demonstrate a high degree of reproducibility. Copyright © 2011 John Wiley & Sons, Ltd.

New world record efficiency for Cu(In,Ga)Se2 thin‐film solar cells beyond 20%

This short communication reports on achieving 18·8% total-area conversion efficiency for a ZnO/CdS/Cu(In,Ga)Se2/Mo polycrystalline thin-film solar cell. We also report a 15%-efficient, Cd-free device fabricated via physical vapor deposition methods. The Cd-free cell includes no buffer layer, and it is fabricated by direct deposition of ZnO on the Cu(In,Ga)Se2 thin-film absorber. Both results have been measured at the National Renewable Energy Laboratory under standard reporting conditions (1000 W/m2, 25°C, ASTM E 892 Global). The 18·8% conversion efficiency represents a new record for such devices (Notable Exceptions) and makes the 20% performance level by thin-film polycrystalline materials much closer to reality. We allude to the enhancement in performance of such cells as compared to previous record cells, and we discuss possible and realistic routes to enhance the performance toward the 20% efficiency level. Published in 1999 by John Wiley & Sons, Ltd. This article is a US government work and is in the public domain in the United States.

Progress toward 20% efficiency in Cu(In,Ga)Se2 polycrystalline thin‐film solar cells

We report a new state of the art in thin-film polycrystalline Cu(In,Ga)Se2-based solar cells with the attainment of energy conversion efficiencies of 19·5%. An analysis of the performance of Cu(In,Ga)Se2 solar cells in terms of some absorber properties and other derived diode parameters is presented. The analysis reveals that the highest-performance cells can be associated with absorber bandgap values of ∼1·14 eV, resulting in devices with the lowest values of diode saturation current density (∼3×10−8 mA/cm2) and diode quality factors in the range 1·30   1;20% in thin-film polycrystalline Cu(In,Ga)Se2 solar cells. Published in 2005 John Wiley & Sons, Ltd.

SHORT COMMUNICATION: ACCELERATED PUBLICATION: Diode characteristics in state‐of‐the‐art ZnO/CdS/Cu(In1−xGax)Se2 solar cells

We report on improvements to the energy conversion efficiency of wide bandgap (Eg > 1.2 eV) solar cells on the basis of CuIn1−xGaxSe2. Historically, attaining high efficiency (>16%) from these types of compound semiconductor thin films has been difficult. Nevertheless, by using (a) the alkaline-containing high-temperature EtaMax glass substrates from Schott AG, (b) elevated substrate temperatures of 600–650 °C, and (c) high vacuum evaporation from elemental sources following National Renewable Energy Laboratory's three-stage process, we have been able to improve the performance of wider bandgap solar cells with 1.2  18% for absorber bandgaps of ~1.30 eV and efficiencies of ~16% for bandgaps up to ~1.45 eV. In comparing J–V parameters in similar materials, we establish gains in the open-circuit voltage and, to a lesser degree, the fill factor value, as the reason for the improved performance. The higher voltages seen in these wide gap materials grown at high substrate temperatures are due to reduced recombination. We establish the existence of random and discrete grains within the CIGS absorbers that yield limited or no generation/collection of minority carriers. We also show that interfacial recombination is the main mechanism limiting additional enhancements to open-circuit voltage and therefore performance. Solar cell results, absorber materials characterization, and experimental details and discussion are presented. Copyright © 2012 John Wiley & Sons, Ltd.

Wide Bandgap Cu(In,Ga)Se2 Solar Cells with Improved Energy Conversion Efficiency

The growth and characterization of Cu(In,Ga)Se/sub 2/ polycrystalline thin film solar cells under the presence of thin-MF (M=Na, K, Cs) precursor layers is presented. Some electrical, structural and electronic absorber properties due to the presence of such Group Ia impurities are quantified along with their influence in device performance. The authors present a growth model for the role of Na in Cu(In,Ga)Se/sub 2/ that attributes the enhancements in electrical conductivity and photovoltaic device performance to the extinction of a finite number of donor states (i.e., In/sub Cu/) at the bulk and grain-boundary regions.

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Brian Egaas

Papers

19·9%‐efficient ZnO/CdS/CuInGaSe2 solar cell with 81·2% fill factor

Progress toward 20% efficiency in Cu(In,Ga)Se2 polycrystalline thin‐film solar cells

SHORT COMMUNICATION: ACCELERATED PUBLICATION: Diode characteristics in state‐of‐the‐art ZnO/CdS/Cu(In1−xGax)Se2 solar cells

Wide Bandgap Cu(In,Ga)Se2 Solar Cells with Improved Energy Conversion Efficiency

On the role of Na and modifications to Cu(In,Ga)Se/sub 2/ absorber materials using thin-MF (M=Na, K, Cs) precursor layers [solar cells]