Numerical Simulation of Solar Cells and Solar Cell Characterization Methods: the Open-Source on Demand Program AFORS-HET

Within this chapter, the principles of numerical solar cell simulation are described, usingAFORS HET automat for simulation of heterostructures . AFORS HET is a onedimensional numerical computer program for modelling multi layer homo orheterojunction solar cells as well as some common solar cell characterization methods.Solar cell simulation subdivides into two parts optical and electrical simulation. By opticalsimulation the local generation rate G x, t within the solar cell is calculated, that is thenumber of excess carriers electrons and holes that are created per second and per unitvolume at the time t at the position x within the solar cell due to light absorption.Depending on the optical model chosen for the simulation, effects like external or internalreflections, coherent superposition of the propagating light or light scattering at internalsurfaces can be considered. By electrical simulation the local electron and hole particledensities n x, t , p x, t and the local electric potential amp; 981; x, t within the solar cell arecalculated, while the solar cell is operated under a specified condition for example operatedunder open circuit conditions or at a specified external cell voltage . From that, all otherinternal cell quantities, such like band diagrams, local recombination rates, local cellcurrents and local phase shifts can be calculated. In order to perform an electricalsimulation, 1 the local generation rate G x, t has to be specified, that is, an opticalsimulation has to be done, 2 the local recombination rate R x, t has to be explicitly statedin terms of the unknown variables n, p, amp; 981; , R x, t f n, p, amp; 981; . This is a recombination modelhas to be chosen. Depending on the recombination model chosen for the simulation, effectslike direct band to band recombination radiative recombination , indirect band to bandrecombination Auger recombination or recombination via defects Shockley Read Hallrecombination, dangling bond recombination can be considere

Review and evaluation of past solar cell development efforts

Bibliography on photovoltaic effect and solar cell developmen

Silicon Based Thin Film Solar Cells

Silicon Based Thin Film Solar Cells explains concepts related to technologies for silicon (Si) based photovoltaic applications. Topics in this book focus on ‘new concept’ solar cells. These kinds of cells can make photovoltaic power production an economically viable option in comparison to the bulk crystalline semiconductor technology industry. A transition from bulk crystalline Si solar cells toward thin-film technologies reduces usage of active material and introduces new concepts based on nanotechnologies. Despite its importance, the scientific development and understanding of new solar cells is not very advanced, and educational resources for specialized engineers and scientists are required. This textbook presents the fundamental scientific aspects of Si thin films growth technology, together with a clear understanding of the properties of the material and how this is employed in new generation photovoltaic solar cells. The textbook is a valuable resource for graduate students working on their theses, young researchers and all people approaching problems and fundamental aspects of advanced photovoltaic conversion

An investigation of electrical and optical properties of reactively sputtered silicon nitride and amorphous hydrogenated silicon thin films

Thin films of silicon nitride and amorphous hydrogenated silicon were prepared by radio frequency reactive sputter deposition and their properties optimized for their use as low temperature passivation coatings for optoelectronic devices. The effect of various sputter deposition parameters on the conduction and optical properties were studied. Infrared spectrophotometry and ellipsometry were used to determined the optical properties of the films whereas the electrical properties were determined from current-voltage measurements of MIS capacitors. Typical parameters of a sputter deposition run for the best Si3N4 films were: base pressure, 1-2x10-6 torr; sputtering pressure, 5 mtorr; nitrogen partial pressure, 16.5%; cathode anode gap, 10 cm; target power density, 1.97watts/cm2; and cathode voltage, 1.0 kvolts. Films of thickness 50-120nm, refractive index 1.94-2.2, and low conductivity (resistivity of 1011 Ω-cm) were obtained. The deposition rate was in the ranged of 5-8 nm/min depending on the sputtering pressure, the appied target power, and the nitrogen partial pressure. It was concluded that the quality of the silicon nitride films is strongly dependent on the total deposition pressure, nitrogen partial pressure, applied target power voltage, and possibly cathode voltage. It was also concluded that the water vapor background was the major factor in increasing the conductivity of the best films to values about three orders of magnitude above those for the best bulk silicon nitride material. Typical sputtering parameters for depositing a-Si:H films were: base pressure, 1-2x10-6 torr; sputtering pressure, 7 mtorr; hydrogen partial pressure, 5-20%; cathode anode gap, 7.6 cm; r.f. target power density, 1.58-1.82 watts/cm2; cathode voltage, 1.8-1.9 kvolts. Films of thicknesses 78-150 nm, refractive index 3.25 - 4.0, and strong absorption at 2000 cm-1 of infrared spectra were obtained. It was concluded that stoichiometric a -Si:H films can be prepared by reactive sputtering of a silicon target in the environment of argon and hydrogen

Solar cell radiation handbook

The handbook to predict the degradation of solar cell electrical performance in any given space radiation environment is presented. Solar cell theory, cell manufacturing and how they are modeled mathematically are described. The interaction of energetic charged particles radiation with solar cells is discussed and the concept of 1 MeV equivalent electron fluence is introduced. The space radiation environment is described and methods of calculating equivalent fluences for the space environment are developed. A computer program was written to perform the equivalent fluence calculations and a FORTRAN listing of the program is included. Data detailing the degradation of solar cell electrical parameters as a function of 1 MeV electron fluence are presented

Nanophotonic Devices Based on Indium Phosphide Nanopillars Grown Directly on Silicon

III-V optoelectronic device integration in a CMOS post-process compatible manner is important for the intimate integration of silicon-based electronic and photonic integrated circuits. The low temperature, self-catalyzed growth of high crystalline quality Wurtzite-phase InP nanopillars directly on silicon presents a viable approach to integrate high performance nano-optoelectronic devices.For the optical transmitter side of the photonic link, InGaAs quantum wells have been grown in a core-shell manner within InP nanopillars. Position-controlled growth with varying pitch is used to systematically control emission wavelength across the same growth substrate. These nanopillars have been fabricated into electrically-injected quantum well in nanopillar LEDs operating within the silicon transparent 1400-1550 nm spectral window and efficiently emitting micro-watts of power. A high quality factor (Q ~ 1000) undercut cavity quantum well nanolaser is demonstrated, operating in the silicon-transparent wavelength range up to room temperature under optical excitation.We also demonstrate an InP nanopillar phototransistor as a sensitive, low-capacitance photoreceiver for the energy-efficient operation of a complete optical link. Efficient absorption in a compact single nanopillar InP photo-BJT leads to a simultaneously high responsivity of 9.5 A/W and high 3dB-bandwidth of 7 GHz.For photovoltaic energy harvesting, a sparsely packed InP nanopillar array can absorb ~90% of the incident light because of the large absorption cross section of these near-wavelength nanopillars. Experimental data based on wavelength and angle resolved integrating sphere measurements will be presented to discuss the nearly omnidirectional absorption properties of these nanopillar arrays

Integration of Antennas and Solar cells for Low Power Wireless Systems

This thesis reports on design methods for enhanced integration of low-profile antennas for short-range wireless communications with solar voltaic systems. The need to transform to more sustainable energy sources arises from the excessive production of harmful carbon emissions from fossil fuels. The Internet of Things and the proliferation of battery powered devices makes energy harvesting from the environment more desirable in order to reduce dependency on the power grid and running costs. While photovoltaic powering is opportune due to immense levels of available solar power, the separate area requirements for the antenna and the photovoltaic surfaces presents an opportunity to significantly minimize the unit volume and to enable portable deployment. The focus is on issues of integrating antennas and transmission lines above crystalline silicon solar cells, in particular, the relative orientations are complicated by a-symmetric lattice of the solar cell. A solution to minimise orientation sensitivity was provided and utilised to successfully isolate a microstrip transmission line from the solar lattice, thereby allowing four antenna configurations to be demonstrated. Further work on crystalline solar cells demonstrated their use alongside circularly polarised antennas for aerial vehicles. Wireless energy harvesting over a wide frequency range was demonstrated with an a-Si solar Vivaldi antenna. A dye-sensitised solar dipole antenna was developed for low power indoor applications. The approaches established the engineering capacity to reduce the device size and weight through integration of the radio and the solar cell technologies. In addition, the use of different solar cell technologies demonstrated the importance of selecting the cell type most suited to the intended application

Solar Cell High Efficiency and Radiation Damage

Silicon solar cell analysis and fundamental measurements, silicon cell technology, gallium arsenide research and technology, and radiation effects on silicon and gallium arsenide cells, are reported

Influence of processing conditions on morphology and performance of vacuum deposited organic solar cells

This thesis discusses vacuum deposited organic solar cells. It focuses on the investigation of new donor molecules blended with the standard electron acceptor C60. These donor-acceptor heterojunctions form the photoactive system of organic solar cells. In addition, the influence of the processing conditions on the morphology of the blend layers is investigated, as the morphology is crucial for an efficient generation of free charge carriers upon photon absorption. Bulk heterojunction solar cells with the donor DTDCTB are deposited at different substrate temperatures. We identify three substrate temperature regimes, discriminated by the behavior of the fill factor (FF ) as a function of the blend layer thickness. Devices deposited at RT have a maximum FF between 50 and 70 nm blend thickness, while devices deposited at 110 °C have a monotonically decreasing FF. At Tsub=85 °C, the devices have an S-kinked current-voltage curve. Grazing incidence wide angle X-ray scattering measurements show that this peculiar behavior of the FF is not correlated with a change in the crystallinity of the DTDCTB, which stays amorphous. Absorption measurements show that the average alignment of the molecules inside the blend also remains unchanged. Charge extraction measurements (OTRACE) reveal a mobility for the 110 °C device that is an order of magnitude higher than for the RT device. The difference in mobility can be explained by a higher trap density for the RT samples as measured by impedance spectroscopy. Despite slightly higher carrier lifetimes for the RT device obtained by transient photovoltage measurements, its mobility-lifetime product is still lower than for the 110 °C devices. Based on DTDCTB, three new donor materials are designed to have a higher thermal stability in order to achieve higher yields upon material purification using gradient sublimation. For PRTF, the thermal stability is increased demonstrated by a higher yield upon sublimation. However, all new materials have a reduced absorption as compared to DTDCTB, which limits the short current density, and the FF is more sensitive to an increase of the blend layer thickness. The highest power conversion efficiency is achieved for a PRTF:C60 solar cell with 3.8%. Interestingly, PRTF:C60 solar cells show exceptionally low nonradiative voltage losses of only 0.26 V. Another absorber molecule is the push-pull chromophore QM1. Scanning electron microscope (SEM) measurements show a growth of the molecule in nanowires on several substrates. The nanowires have lengths up to several micrometers and are several tens of nanometers wide. The formation of the nanowires is accompanied by a strong blue shift (650 meV) of the thin film absorption spectrum in comparison to the absorption in solution, which is attributed to H-aggregation of the molecules. Furthermore, the thin film absorption onset reaches up to 1100 nm, making the material a suitable candidate for a near infrared absorber in organic solar cells. For a solar cell in combination with C60, a power conversion efficiency of 1.9% was achieved with an external quantum efficiency of over 19% for the spectral range between 600 and 1000 nm. The method of “co-evaporant induced crystallization” as a means to increase the crystallinity of blend layers without increasing the substrate temperature during the deposition is investigated. Mass spectrometry (LDI-ToF-MS) measurements show that polydimethylsiloxane (PDMS), which is used as a co-evaporant, decomposes during the evaporation and only lighter oligomers evaporate. Quartz crystal microbalance (QCM) measurements prove that the detection of PDMS saturates at higher amounts of evaporated material. LDI-ToF-MS measurements show further that the determination of the volatilization temperature by QCM measurements is highly error prone. The method was applied to zinc phthalocyanine (ZnPc) :C60 solar cells, accepting the insertion of PDMS into the blend layer. Diffraction (GIXRD) measurements show a large increase in crystallinity. ZnPc:C60 solar cells produced by applying the method reveal a similar behavior as solar cells processed at a higher substrate temperature