Photovoltaics

Determination of the optimal tilt angle and orientation for solar photovoltaic arrays

by Eugenia Mehleri

BariumCopperChFluorine (Ch= Sulfur, Selenium, Tellurium) p-type transparent conductors

by Andriy Zakutayev

Thesis (Ph.D.)--Oregon State University, 2010.;ISBN: 9781124216355

BaCuChF (Ch = S, Se, Te) materials are chalcogen-based transparent conductors with wide optical band gaps (2.9 – 3.5... more BaCuChF (Ch = S, Se, Te) materials are chalcogen-based transparent conductors with wide optical band gaps (2.9 – 3.5 eV) and a high concentration of free holes (10¹⁸ – 10²⁰ cm⁻³) caused by the presence of copper vacancies. Chalcogen vacancies compensate copper vacancies in these materials, setting the Fermi level close to the valence band maximum. BaCuChF thin film solid solutions prepared by pulsed laser deposition (PLD) have tunable properties, such as lattice constants, conductivity and optical band gaps. BaCuSF and BaCuSeF materials also feature room-temperature stable 3D excitons with spin-orbit-split levels. BaCuTeF has forbidden lowest-energy optical transitions which extends its transparency range. BaCuChF surfaces oxidize when exposed to air, but can be protected using Ch capping layers. Polycrystalline BaCuSeF thin films have a 4.85 eV work function, a 0.11 eV hole injection barrier into ZnPc, and 0.00 eV valence band offset with ZnTe. BaCuSeF should have s similar band offset and similar interfacial properties with CdTe and Cu(InGa)Se₂, and BaCuSF should have no valence band offset with Cu₂ZnSnS₄, according to the transitivity rule. Therefore, BaCuSeF is suitable for applications as a p-layer in organic light-emitting diodes, p-i-n double-heterojunction and tandem chalcogenide solar cells.

Zn–Ni–Co–O wide-band-gap p-type conductive oxides with high work functions

by Andriy Zakutayev

MRS Communications 1, 23 (2011)

Band-structure, optical properties, and defect physics of the photovoltaic semiconductor SnS

by Andriy Zakutayev

Appl. Phys. Lett. 100, 032104 (2012

Absence of carrier recombination associated with the defect pool model in a-Si:H i-layers: Evidence from current-voltage characteristics on p-i-n and n-i-p solar cells

by Joshua Pearce

J. Deng, J. M. Pearce, R. J. Koval, V. Vlahos, R.W. Collins, and C. R. Wronski, "Absence of carrier recombination associated with the defect pool model in a-Si:H i-layers: Evidence from current-voltage characteristics on p-i-n and n-i-p solar cells", Applied Physics Letters, 82(18), pp. 3023-3025, 2003. http://link.aip.org/link/doi/10.1063/1.1571985

Forward bias current–voltage characteristics (JD–V) were studied for both p–i–n (superstrate) and n–i–p (substrate)... more Forward bias current–voltage characteristics (JD–V) were studied for both p–i–n (superstrate) and n–i–p (substrate) (a-SiC:H p)/(a-Si:H i) solar-cell structures having different p/i interface layers and different thickness i-layers. Contributions of the p/i interfaces to the JD–V characteristics were separated, and the dependence on the thickness of the i-layers was established. Equivalence was observed in a comparison of the characteristics of p–i–n and n–i–p cells. The various JD–V characteristics are found to be consistent with uniform densities of defects in the i-layers, and thus inconsistent with the spatially varying large densities of defects predicted for solar-cell structures by the defect pool model.

Maximization of the open circuit voltage for a-Si:H n-i-p solar cells by incorporation of protocrystalline Si:H p-type layers

by Joshua Pearce

R. J. Koval, Chi Chen, G. M. Ferreira, A. S. Ferlauto, J. M. Pearce, P.I. Rovira, R. W. Collins, and C.R. Wronski, "Maximization of the open circuit voltage for a-Si:H n-i-p solar cells by incorporation of protocrystalline Si:H p-type layers", Applied Physics Letters, 81(7) 1258-1260, 2002. http://link.aip.org/link/doi/10.1063/1.1499735

In studies of hydrogenated amorphous silicon (a-Si:H) n–i–p solar cells fabricated by rf plasma-enhanced chemical... more In studies of hydrogenated amorphous silicon (a-Si:H) n–i–p solar cells fabricated by rf plasma-enhanced chemical vapor deposition (PECVD), we have found that the maximum open circuit voltage (Voc) is obtained by incorporating p-type doped Si:H layers that are protocrystalline in nature. Specifically, these optimum p layers are prepared by PECVD in the a-Si:H growth regime using the maximum hydrogen-to-silane flow ratio possible without crossing the thickness-dependent transition into the mixed-phase (amorphous+microcrystalline) growth regime for the ∼200 Å p-layer thickness. The strong dependence of the p-layer phase and solar cell Voc on the underlying i-layer phase also confirms the protocrystalline nature of the optimum Si:H p layer.

Dependence of open circuit voltage in protocrystalline Si:H solar cells on carrier recombination in p/i interface and bulk regions

by Joshua Pearce

Joshua M. Pearce, Randy J. Koval, Andre S. Ferlauto, Robert W. Collins, Christopher R. Wronski, Jeffrey Yang, and Subhendu Guha, "Dependence of open circuit voltage in protocrystalline Si:H solar cells on carrier recombination in p/i interface and bulk regions", Appl. Phys. Lett. 77, 3093-3095, 2000. http://link.aip.org/link/?APPLAB/77/3093/1

Contribution of carrier recombination from the p/i interface regions and the bulk to the dark current–voltage (JD–V)... more Contribution of carrier recombination from the p/i interface regions and the bulk to the dark current–voltage (JD–V) and short-circuit current–open-circuit voltage (Jsc–Voc) characteristics of hydrogenated amorphous-silicon (a-Si:H) p–i–n and n–i–p solar cells have been separated, identified, and quantified. Results are presented and discussed here which show that a maximum 1 sun Voc for a given bulk material can be validly extrapolated from bulk dominated Jsc–Voc characteristics at low illumination intensities.

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

by Joshua Pearce

A. S. Ferlauto, G. M. Ferreira, J. M. Pearce, C.R. Wronski, R. W. Collins, Xunming Deng, and Gautam Ganguly, "Analytical model for the optical functions of amorphous semiconductors from the near-infrared to ultraviolet: Applications in thin film photovoltaics", Journal of Applied Physics, 92(5), 2424-2436, 2002. http://link.aip.org/link/?JAPIAU/92/2424/1

We have developed a Kramers–Kronig consistent analytical expression to fit the measured optical functions of... more 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 (ϵ1,ϵ2) (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 (ϵ1,ϵ2) 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 (ϵ1,ϵ2) can be simulated assuming a single Lorentz oscillator. The expression developed here provides an improved description of ϵ2 (or α) in the below-band gap and near-band gap regions compared with previous approaches. Although the expression is more complicated analytically, it has numerous applications in the analysis and simulation of thin film a-Si:H based p-i-n and n-i-p multilayer photovoltaic devices. First, we describe an approach whereby, from a single accessible measure of the optical band gap, the optical functions can be generated over the full solar spectrum for a sample set consisting of the highest quality intrinsic a-Si:H based alloys prepared by plasma-enhanced chemical vapor deposition using the principle of maximal H2 dilution. Second, we describe quantitatively how such an approach can be modified for sample sets consisting of lower quality alloy materials. Finally, we demonstrate how the generated optical functions can be used in simulations of the absorption, reflection, and quantum efficiency spectra of a-Si:H based single-junction and multijunction solar cells. © 2002 American Institute of Physics.

Institutional-Scale Operational Symbiosis of Photovoltaic and Cogeneration Energy Systems

by Joshua Pearce

M. Mostofi, A. H. Nosrat, and J. M. Pearce, “Institutional-Scale Operational Symbiosis of Photovoltaic and Cogeneration Energy Systems” International Journal of Environmental Science and Technology  8(1), pp. 31-44, 2011.

Due to the negative environmental effects of fossil fuel combustion, there is a growing interest in both improved... more Due to the negative environmental effects of fossil fuel combustion, there is a growing interest in both improved efficiency in energy management and a large-scale transition to renewable energy systems. Using both of these strategies, a large institutional-scale hybrid energy system is proposed here, which incorporates both solar photovoltaic energy conversion to supply renewable energy and cogeneration to improve efficiency. In this case, the photovoltaic reduces the run time for the cogeneration to meet load, particularly in peaking air conditioning times. In turn, however, the cogeneration system is used to provide power back up for the photovoltaic during the night and adverse weather conditions. To illustrate the operational symbiosis between these two technical systems, this study provides a case study of a hybrid photovoltaic and cogeration system for the Taleghani hospital in Tehran. Three design scenarios using only existing technologies for such a hybrid system are considered here:1) single cogeneration + photovoltaic, 2) double cogeneration + photovoltaic, 3) single cogeneration + photovoltaic + storage. Numerical simulations for photovoltaic and cogeneration performance both before and after incorporating improved thermal energy management and high efficiency lighting were considered. The results show that the total amount of natural gas required to provide for the hospitals needs could be lowered from the current status by 55 % for scenario 1 and 62 % for both scenarios 2 and 3, respectively. This significant improvement in natural gas consumption illustrates the potential of hybridizing solar photovoltaic systems and cogeneration systems on a large scale.

Optimizing Design of Household Scale Hybrid Solar Photovoltaic + Combined Heat and Power Systems for Ontario

by Joshua Pearce

P.  Derewonko and J.M. Pearce, “Optimizing Design of Household Scale Hybrid Solar Photovoltaic + Combined Heat and Power Systems for Ontario”, Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE, pp.1274-1279, 7-12 June 2009. http://dx.doi.org/10.1109/PVSC.2009.5411247

This paper investigates the feasibility of implementing a hybrid solar photovoltaic (PV) + combined heat and power... more This paper investigates the feasibility of implementing a hybrid solar photovoltaic (PV) + combined heat and power (CHP) and battery bank system for a residential application to generate reliable base load power to the grid in Ontario. Deploying PV on a large-scale has a penetration level threshold due to the inherent power supply intermittency associated with the solar resource. By creating a hybrid PV+CHP system there is potential of increasing the PV penetration level. One year of one second resolution pyranometer data is analyzed for Kingston Ontario to determine the total amount of PV energy generation potential, the rate of change of PV power generation due to intermittent cloud cover, and the daily CHP run time required to supply reliable base load power to the grid using this hybrid system. This analysis found that the vast majority of solar energy fluctuations are small in magnitude and the worst case energy fluctuation can be accommodated by relatively inexpensive and simple storage with conventional lead-acid batteries. For systems where the PV power rating is identical to the CHP unit, the CHP unit must run for more than twenty hours a day for the system to meet the base load requirement during the winter months. This provides a fortunate supply of heat, which can be used for the needed home heating. This paper provides analysis for a preliminary base line system.

New insight into the regeneration kinetics of organic dye sensitised solar cells

by Stefano Martiniani

Stefano Martiniani ,  Assaf Y. Anderson ,  ChunHung Law ,  Brian C. O'Regan and Claudia Barolo
Chem. Commun., 2012, 48, 2406-2408
DOI: 10.1039/C2CC17100G

The order of regeneration for DSCs based on two organic dyes has been investigated by transient absorption... more The order of regeneration for DSCs based on two organic dyes has been investigated by transient absorption spectroscopy on devices under operating conditions and determined to be 2nd order in iodide. The results shed light on the mechanism and limits to the regeneration rate relative to oxidation potential.

Diverting Indirect Subsidies from the Nuclear Industry to the Photovoltaic Industry: Energy and Economic Returns

by Joshua Pearce

I. Zelenika-Zovko and J. M. Pearce,  “Diverting Indirect Subsidies from the Nuclear Industry to the Photovoltaic Industry: Energy and Economic Returns”, Energy Policy 39, pp. 2626–2632 (2011).

Nuclear power and solar photovoltaic energy conversion often compete for policy support that governs economic... more Nuclear power and solar photovoltaic energy conversion often compete for policy support that governs economic viability. This paper compares current subsidization of the nuclear industry with providing equivalent support to manufacturing photovoltaic modules. Current U.S. indirect nuclear insurance subsidies are reviewed and the power, energy and financial outcomes of this indirect subsidy are compared to equivalent amounts for indirect subsidies (loan guarantees) for photovoltaic manufacturing using a model that holds economic values constant for clarity. The preliminary analysis indicates that if only this one relatively ignored indirect subsidy for nuclear power was diverted to photovoltaic manufacturing, it would result in more installed power and more energy produced by mid-century. By 2110 cumulative electricity output of solar would provide an additional 48,600 TWh over nuclear worth $5.3 trillion. The results clearly show that not only does the indirect insurance liability subsidy play a significant factor for nuclear industry, but also how the transfer of such an indirect subsidy from the nuclear to photovoltaic industry would result in more energy over the life cycle of the technologies.

Solar Photovoltaic Energy for Mitigation of Climate Change: A Catalytic Application of Catholic Social Thought

by Joshua Pearce

Joshua M. Pearce, Anna L. Santini, and Jennifer M. Desilva, “Solar Photovoltaic Energy for Mitigation of Climate Change: A Catalytic Application of Catholic Social Thought”, Worldviews, Volume 13(1), pp. 92-118, 2009.

This paper explores an application of Catholic theology to mitigate the current destruction of God's creation underway... more This paper explores an application of Catholic theology to mitigate the current destruction of God's creation underway due to global climate destabilization. Specifically it describes the possibility of the U.S. Catholic Church adopting a systematic plan to catalyze the world energy market to shift to solar photovoltaic energy, a non-polluting renewable energy source. The science behind the ecological crisis and climate change in the context of the Catholic basis for environmental stewardship is summarized to provide a moral foundation for the plan. Then, the viability and ramifications of integrating solar photovoltaic systems in all U.S. Catholic Churches is analyzed from technical, economic, and ethical perspectives.

Leveraging Photovoltaic Technology for Sustainable Development in Ontario's First Nations Communities

by Joshua Pearce

Dirk V. P. McLaughlin, Nicole C. McDonald, Ha T. Nguyen and J. M. Pearce, “Leveraging Photovoltaic Technology for Sustainable Development in Ontario's First Nations Communities”, Journal of Sustainable Development 3(3), pp. 3-13, 2010.

The Ontario feed-in tariff (FIT) for solar photovoltaic (PV) technology has provided Ontario's Aboriginal communities... more The Ontario feed-in tariff (FIT) for solar photovoltaic (PV) technology has provided Ontario's Aboriginal communities with an opportunity to i) weaken the cycle of poverty; ii) directly counteract climate change by producing renewable energy; and iii) become more self-sufficient. This paper critically analyzes the technical, cultural, and economic viability of leveraging the FIT for PV to provide green electricity and revenue to assist First Nations communities in sustainable development. A generalized free GIS-energy-based protocol was developed to determine the PV potential for Aboriginal communities. This model was applied to a case study of the Constance Lake First Nations community and an economic analysis showed financially-viable rates of return over 20 years. By generalizing these findings to Ontario, the potential PV deployment on First Nation rooftops alone is over 200MW, which clearly provides an opportunity for developing pride associated with owning a community-led, environmentally beneficial, local energy project.

Cleaner production via industrial symbiosis in glass and largescale solar photovoltaic manufacturing

by Joshua Pearce

Amir H. Nosrat, Jack Jeswiet, and Joshua M. Pearce, “Cleaner Production via Industrial Symbiosis in Glass and Large-Scale Solar Photovoltaic Manufacturing” Proceedings 2009 IEEE Toronto International Conference – Science and Technology for Humanity (TIC-STH), pp. 967-970.

In order to alleviate production costs and increase the environmental performance of solar photovoltaic manufacturing,... more In order to alleviate production costs and increase the environmental performance of solar photovoltaic manufacturing, an eco-industrial park for GW-scale production of PV is proposed. This article quantifies the inputs and outputs for the glass manufacturing component of such a system using standard manufacturing techniques. Utilizing industrial symbiosis in this way, potential reductions for such a plant were found to be about 30,000 tons/year in raw materials and over 220,000 GJ/year in embodied energy.

Correlation of Light-Induced Changes in a-Si:H Films with Characteristics of Corresponding Solar Cells

by Joshua Pearce

J. M. Pearce, R. J. Koval, R.W. Collins, C. R. Wronski, M.M. Al-Jassim, and K.M. Jones "Correlation of Light-Induced Changes in a-Si:H Films with Characteristics of Corresponding Solar Cells" 29th IEEE Photovoltaic Specialists Conf. Proc., (IEEE, 2002) pp. 1098-1101, 2002.

For the first time direct correlations are obtained between the light induced changes under 1 sun illumination in the... more For the first time direct correlations are obtained between the light induced changes under 1 sun illumination in the properties of a-Si:H and those in the characteristics of p-i-n cells incorporating identically-prepared i-layers. These correlations were obtained after account was taken of the effects that the location of the electron and hole quasi-Fermi levels have on the carrier recombination that occurs through the different gap states. The changes in midgap state density, as measured on the films and reflected in the subgap absorption at 1.2 eV, are directly correlated with changes in the dark I-V characteristics under low forward bias. In this case small quasi-Fermi level splitting is present so the recombination of the injected carriers is determined by the midgap states in the bulk of the i-layer. In addition, the changes in the electron mobility-lifetime products as measured on the films are correlated with changes in the fill factor measured on cells under the same conditions as long as large quasi-Fermi level splitting is present and recombination occurs through states spanning a wide region of the gap, such as occurs under 1 sun illumination. The results explain (i) the failure of numerous attempts to correlate the degradation of solar cells reliably with the creation of dangling bond defects and (ii) the inadequacy of the large number of modeling results that assume such a correlation.

Microstructurally Engineered p-layers for Obtaining High Open-Circuit Voltages in a-Si:H n-i-p Solar Cells

by Joshua Pearce

R. J. Koval, J. M. Pearce, Chi Chen, G. M. Ferreira, A. S. Ferlauto, R. W. Collins, and C.R. Wronski, "Microstructurally Engineered p-layers for Obtaining High Open-Circuit Voltages in a-Si:H n-i-p Solar Cells", 29th IEEE Photovoltaic Specialists Conf. Proc., (IEEE, 2002) pp. 1090-1093, 2002.

A study was carded out with the goal of obtaining high open circuit voltages (Voc) in a-Si:H n-i-p solar cells, taking... more A study was carded out with the goal of obtaining high open circuit voltages (Voc) in a-Si:H n-i-p solar cells, taking into account the evolutionary nature of the microstructure of the p-layers during growth. It is found that cells with players in the protocrystalline Si:H growth regime give the highest values of Voc not those with microcrystalline Si:H p-layers. Evidence for this conclusion is presented whereby Voc is related directly to the microstructure of the p-layers, as characterized using spectroscopic ellipsometry, atomic force microscopy, and electrical measurements. The results clarify the origins of (i) inconsistencies associated with attributing high Voc in n-i-p cells to the microcrystallinity of the p-layers, as well as (ii) the inability to obtain similarly high values in p-i-n superstrate cells. Because the microstructure of p-type protocrystalline Si:H depends on that of the underlying i-layer, it is not possible to optimize the cell parameters based on an understanding of the process unless detailed characterization of the p-layer in the actual cell configuration is performed.

Quantitative Correlation of High Quality a-Si:H p-i-n Solar Cell Characteristics with Properties of the Bulk and p/i Interface Region

by Joshua Pearce

J. M. Pearce, R. J. Koval, R.W. Collins, and C.R. Wronski, "Quantitative Correlation of High Quality a-Si:H p-i-n Solar Cell Characteristics with Properties of the Bulk and p/i Interface Region", 28th IEEE Photovoltaic Specialists Conf. Proc., (IEEE, 2000) pp. 944-947, 2000.

Studies have been carried out on high quality hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells with... more Studies have been carried out on high quality hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells with protocrystalline i-layers to establish the nature of p/i interfaces and to quantify their contributions to various solar cell characteristics. The p-a-SiC:H,B/i-a-Si:H/n-μcSi:H,P cell structures used had the a-Si:H i-layers deposited from hydrogen diluted silane with R≡[H2 ]/[SiH4]=10. The high quality p/i interface regions obtained with R=10, indicated by the high and stable open circuit voltage (Voc) values, were further improved by increasing R in the 200 Å of a-Si:H adjacent to the a-SiC:H layer. From the systematic improvement and ability to obtain p/i interface regions with outstanding quality, it was possible to track their contributions to cell characteristics relative to those from the bulk. Results of dark current voltage (JD-V) and short circuit current-open circuit voltage (Jsc-Voc) characteristics are presented which clearly demonstrate that even high quality interface regions in p-i-n cells can mask some contributions of protocrystalline bulk layers. Results are also presented and discussed on how the relative contributions of bulk and p/i interfaces can be isolated and quantified so they can be used as inputs for reliable analysis of solar cell characteristics

The Role of Phase Transitions in Protocrystalline Si:H on the Performance their of Solar Cells

by Joshua Pearce

R. J. Koval, J. M. Pearce, A.S. Ferlauto, P.I. Rovira, R.W. Collins, and C.R. Wronski, "The Role of Phase Transitions in Protocrystalline Si:H on the Performance their of Solar Cells", 28th IEEE Photovoltaic Specialists Conf. Proc., (IEEE, 2000) pp. 750-753, 2000.

A systematic study has been carried out to quantify the effect of microcrystallite nucleation in the intrinsic layer... more A systematic study has been carried out to quantify the effect of microcrystallite nucleation in the intrinsic layer of protocrystalline Si:H p-i-n solar cells prepared by rf plasma enhanced chemical vapor deposition (PECVD). Real-time spectroscopic ellipsometry (RTSE) results that have previously identified the transitions from amorphous to microcrystalline phase were confirmed with atomic force microscopy (AFM) images. The effects of the phase transitions in the bulk intrinsic layer, as well as near the p/i interface of p-i-n cells, have been evaluated as a function of film thickness and H2-dilution ratio (R=[H2]/[SiH4]). Illuminated and dark J-V characteristics are correlated with the microstructural evolution of the Si:H films yielding insight into the “sharpness” of the transition. Evidence of abrupt changes in the mobility gap is obtained from the selfconsistent numerical modeling of cell characteristics.

The Application of LiDAR to Assessment of Rooftop Solar Photovoltaic Deployment Potential on a Municipal District Unit

by Joshua Pearce

Nguyen H.T., Pearce J.M., Harrap R., Barber G. The Application of LiDAR to Assessment of Rooftop Solar Photovoltaic Deployment Potential in a Municipal District Unit. Sensors. 2012; 12(4):4534-4558.

A methodology is provided for the application of Light Detection and Ranging (LiDAR) to automated solar photovoltaic... more A methodology is provided for the application of Light Detection and Ranging (LiDAR) to automated solar photovoltaic (PV) deployment analysis on the regional scale. Challenges in urban information extraction and management for solar PV deployment assessment are determined and quantitative solutions are offered. This paper provides the following contributions: (i) a methodology that is consistent with recommendations from existing literature advocating the integration of cross-disciplinary competences in remote sensing (RS), GIS, computer vision and urban environmental studies; (ii) a robust methodology that can work with low-resolution, incomprehensive data and reconstruct vegetation and building separately, but concurrently; (iii) recommendations for future generation of software. A case study is presented as an example of the methodology. Experience from the case study such as the trade-off between time consumption and data quality are discussed to highlight a need for connectivity between demographic information, electrical engineering schemes and GIS and a typical factor of solar useful roofs extracted per method. Finally, conclusions are developed to provide a final methodology to extract the most useful information from the lowest resolution and least comprehensive data to provide solar electric assessments over large areas, which can be adapted anywhere in the world.