Steve Albrecht - Academia.edu (original) (raw)
Papers by Steve Albrecht
Applied Physics Letters, 2016
Nature Communications, 2015
The Journal of Physical Chemistry C, 2014
Journal of the American Chemical Society, 2012
A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher... more A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC(70)BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced. Additionally, a 3-fold reduction in non-geminate recombination is measured compared to optimized PCPDTBT blends. As a consequence of reduced non-geminate recombination, the performance of optimized blends of fluorinated PCPDTBT with PC(70)BM is largely determined by the field dependence of free-carrier generation, and this field dependence is considerably weaker compared to that of blends comprising the non-fluorinated polymer. For these optimized blends, a short-circuit current of 14 mA/cm(2), an open-circuit voltage of 0.74 V, and a fill factor of 58% are achieved, giving a highest energy conversion efficiency of 6.16%. The superior device performance and the low band-gap render this new polymer highly promising for the construction of efficient polymer-based tandem solar cells.
physica status solidi (a), 2016
Journal of Accountancy, Apr 1, 2002
Energy Environ. Sci., 2015
It has long been understood that company-specific factors such as having several years of growth ... more It has long been understood that company-specific factors such as having several years of growth and consistent financial performance, being of sufficient size and having good prospects for future success are important determinants of whether or not companies can be successfully listed on the world's major stock exchanges and have access to equity markets. What is less clear is whether or not there are country-specific variables that are also important in determining whether companies have access to those same equity markets. In this paper, we examine the association between market capital of foreign listed companies on the New York Stock Exchange (NYSE) and London Stock Exchanges (LSE) and various country-specific criteria. Particularly, we associate perceived corruption, economic risk, financial risk, political risk and social development with the total market capital of all firms listed from various countries on the NYSE and LSE. Our results indicate that, when examining our total data set of 130 countries together, perceived corruption and social development are the two factors most closely associated with amount of capital raised on the NYSE and LSE. When the countries are segregated into first-, second- and third-world countries, political risk is most important for first-world countries, financial and economic risk are most important for second-world countries and political risk and social development are most important for third-world countries.
Healthcare financial management: journal of the Healthcare Financial Management Association
Unlike crimes that leave easily detectable physical evidence, employee fraud may be difficult to ... more Unlike crimes that leave easily detectable physical evidence, employee fraud may be difficult to detect because often only symptoms of such crimes are readily apparent, and the symptoms may or may not signal actual fraud. This article discusses six categories of symptoms that indicate fraud may have been committed by an employee, and presents a case study example to illustrate symptoms auditors and financial managers should investigate.
The Journal of Physical Chemistry Letters, 2015
Perovskite solar cells with transparent contacts may be used to compensate for thermalization los... more Perovskite solar cells with transparent contacts may be used to compensate for thermalization losses of silicon solar cells in tandem devices. This offers a way to outreach stagnating efficiencies. However, perovskite top cells in tandem structures require contact layers with high electrical conductivity and optimal transparency. We address this challenge by implementing large-area graphene grown by chemical vapor deposition as a highly transparent electrode in perovskite solar cells, leading to identical charge collection efficiencies. Electrical performance of solar cells with a graphene-based contact reached those of solar cells with standard gold contacts. The optical transmission by far exceeds that of reference devices and amounts to 64.3% below the perovskite band gap. Finally, we demonstrate a four-terminal tandem device combining a high band gap graphene-contacted perovskite top solar cell (Eg = 1.6 eV) with an amorphous/crystalline silicon bottom solar cell (Eg = 1.12 eV).
In this paper we provide a general overview of asset misappropriation. We discuss the current sta... more In this paper we provide a general overview of asset misappropriation. We discuss the current state of academic and practical knowledge as it relates to asset misappropriation, including what we currently know about asset misappropriation, what research has been done in this area, what is currently missing from the research, and what additional resources are needed in order to continue
The E-Business Handbook, 2001
Journal of the American Chemical Society
Developing novel materials and device architectures to further enhance the efficiency of polymer ... more Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structure-property relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by...
Advanced Materials
A so called "energy river" originates in the active layer of a bulk-heterojunction sola... more A so called "energy river" originates in the active layer of a bulk-heterojunction solar cell as described in work by D. Neher, K. Vandewal, and co-workers on page 2533. This river contains polymer chains and cools down from its hot origin to a cold front. The riverbank is created by "fullerene walls" with different heights. Flashes create hot electrons in the energy river. These electrons need to decrease in temperature during their refrigerating evolution in the river. The cold electrons on the right side cannot escape the river, hidden by the big fullerene wall, and get lost. The cold electrons on the left side are the "good guys". They are able to splash out of the river and generate electrical power.
Journal of the American Chemical Society, Jan 5, 2014
Developing novel materials and device architectures to further enhance the efficiency of polymer ... more Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structure-property relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by...
Applied Physics Letters, 2016
Nature Communications, 2015
The Journal of Physical Chemistry C, 2014
Journal of the American Chemical Society, 2012
A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher... more A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC(70)BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced. Additionally, a 3-fold reduction in non-geminate recombination is measured compared to optimized PCPDTBT blends. As a consequence of reduced non-geminate recombination, the performance of optimized blends of fluorinated PCPDTBT with PC(70)BM is largely determined by the field dependence of free-carrier generation, and this field dependence is considerably weaker compared to that of blends comprising the non-fluorinated polymer. For these optimized blends, a short-circuit current of 14 mA/cm(2), an open-circuit voltage of 0.74 V, and a fill factor of 58% are achieved, giving a highest energy conversion efficiency of 6.16%. The superior device performance and the low band-gap render this new polymer highly promising for the construction of efficient polymer-based tandem solar cells.
physica status solidi (a), 2016
Journal of Accountancy, Apr 1, 2002
Energy Environ. Sci., 2015
It has long been understood that company-specific factors such as having several years of growth ... more It has long been understood that company-specific factors such as having several years of growth and consistent financial performance, being of sufficient size and having good prospects for future success are important determinants of whether or not companies can be successfully listed on the world's major stock exchanges and have access to equity markets. What is less clear is whether or not there are country-specific variables that are also important in determining whether companies have access to those same equity markets. In this paper, we examine the association between market capital of foreign listed companies on the New York Stock Exchange (NYSE) and London Stock Exchanges (LSE) and various country-specific criteria. Particularly, we associate perceived corruption, economic risk, financial risk, political risk and social development with the total market capital of all firms listed from various countries on the NYSE and LSE. Our results indicate that, when examining our total data set of 130 countries together, perceived corruption and social development are the two factors most closely associated with amount of capital raised on the NYSE and LSE. When the countries are segregated into first-, second- and third-world countries, political risk is most important for first-world countries, financial and economic risk are most important for second-world countries and political risk and social development are most important for third-world countries.
Healthcare financial management: journal of the Healthcare Financial Management Association
Unlike crimes that leave easily detectable physical evidence, employee fraud may be difficult to ... more Unlike crimes that leave easily detectable physical evidence, employee fraud may be difficult to detect because often only symptoms of such crimes are readily apparent, and the symptoms may or may not signal actual fraud. This article discusses six categories of symptoms that indicate fraud may have been committed by an employee, and presents a case study example to illustrate symptoms auditors and financial managers should investigate.
The Journal of Physical Chemistry Letters, 2015
Perovskite solar cells with transparent contacts may be used to compensate for thermalization los... more Perovskite solar cells with transparent contacts may be used to compensate for thermalization losses of silicon solar cells in tandem devices. This offers a way to outreach stagnating efficiencies. However, perovskite top cells in tandem structures require contact layers with high electrical conductivity and optimal transparency. We address this challenge by implementing large-area graphene grown by chemical vapor deposition as a highly transparent electrode in perovskite solar cells, leading to identical charge collection efficiencies. Electrical performance of solar cells with a graphene-based contact reached those of solar cells with standard gold contacts. The optical transmission by far exceeds that of reference devices and amounts to 64.3% below the perovskite band gap. Finally, we demonstrate a four-terminal tandem device combining a high band gap graphene-contacted perovskite top solar cell (Eg = 1.6 eV) with an amorphous/crystalline silicon bottom solar cell (Eg = 1.12 eV).
In this paper we provide a general overview of asset misappropriation. We discuss the current sta... more In this paper we provide a general overview of asset misappropriation. We discuss the current state of academic and practical knowledge as it relates to asset misappropriation, including what we currently know about asset misappropriation, what research has been done in this area, what is currently missing from the research, and what additional resources are needed in order to continue
The E-Business Handbook, 2001
Journal of the American Chemical Society
Developing novel materials and device architectures to further enhance the efficiency of polymer ... more Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structure-property relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by...
Advanced Materials
A so called "energy river" originates in the active layer of a bulk-heterojunction sola... more A so called "energy river" originates in the active layer of a bulk-heterojunction solar cell as described in work by D. Neher, K. Vandewal, and co-workers on page 2533. This river contains polymer chains and cools down from its hot origin to a cold front. The riverbank is created by "fullerene walls" with different heights. Flashes create hot electrons in the energy river. These electrons need to decrease in temperature during their refrigerating evolution in the river. The cold electrons on the right side cannot escape the river, hidden by the big fullerene wall, and get lost. The cold electrons on the left side are the "good guys". They are able to splash out of the river and generate electrical power.
Journal of the American Chemical Society, Jan 5, 2014
Developing novel materials and device architectures to further enhance the efficiency of polymer ... more Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structure-property relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by...