THE PHYSICS OF SOLAR CELLS PDF
and others who require a background in the physical principles of solar cells. The focus is on the basic semiconductor physics relevant to photovoltaics, physical. The physics of solar cells. The photoelectric effect. The physical basis for solar cells is the photoelectric effect (it was the explanation for this for which Einstein. PDF | The book provides an explanation of the operation of photovoltaic devices from a broad perspective that embraces a variety of materials.
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Request PDF on ResearchGate | The Physics of Solar Cells | Photons In, Electrons Out: Basic Principles of PV Electrons and Holes in Semiconductors. Semiconductor solar cells are fundamentally quite simple devices. . Of more consequence to the physics of solar cells, however, is how the periodic crystalline. This book provides a comprehensive introduction to the physics of the photovoltaic cell. It is suitable for undergraduates, graduate students, and researchers.
Yet the solar panel produced the highest pow er w hen it w as stimulated by red light the longest w avelength in the visible spectrum. The research findings suggest that higher energy phot ons generate more heat t o the panel, rather than creating more electrical pow er.
Solar cells produce less pow er at high temperatures, so higher energy photons w ill have a negative effect on the conversion efficiency of cells. Therefore, filtering out those phot ons from w hite light w ill help to reduce the temperature and potentially improve the rate of aging and efficiency of solar cells.
Electricity blackout is a regular occurrence and regardless of the economic status of each household, most neighborhoods experience loss of pow er at least four days a w eek.
I guess this firsthand experience and the global trend to sw itch from polluting fossil fuel to clean and sustainable alternative energy sources inspired me to focus and w ork in the area of sustainable energy systems. The sun is currently one of the cleanest, most abundant and inexpensive sources of energy mainly in the form of thermal and electric energy.
Physics of solar cells
How ever, in order to use the solar electric energy effectively, the cost and efficiency of the present day solar panels has to be improved. This calls for strong research efforts to save the w orld from pollution and to help communities that suffer w ith basic energy shortages. Therefore, to start the first step of the long journey, I decided to carry out an investigation concerning solar panels responses for different input excitations.
I have chosen to explore t he effect of spectral component s of w hite light on silicon solar cells. I chose to carry out this exploration because I w anted to check how different w avelengths of light affect the performance of solar cells such as its photon absorption ability and electrical pow er output and to try to develop a method that w ould help increase solar cells efficiency.
White light is a composition of photons w ith w avelengths from nm to nm. By using dispersion techniques such as light dispersion prism or color slits, these phot ons reveal themselves to our naked eye in the form of distinct colors arranged in a specific order: red, orange, yellow , green, blue, indigo, violet as show n in Figure 1. These colors in turn represent photons of different w avelengths and energies. Light is an emission of photons in the visible spectra.
Photons do not have electric charge or rest mass; they are field particles that are thought t o be t he carriers of the electromagnetic field. Therefore, we can better study them through their w ave behavior. Thus, as frequency increases w ith a corresponding decrease in w avelength , the photon energy increases and vice versa. When a photon excites an atom see Figure 1. In a typical crystalline silicon solar cell, the majority of the substance is made up of silicon doped w ith a small amount of boron to give it positive or p-type character.
A thin layer on the top of the cell is doped with phosphorus to give it a negative or n-type character. The junction or the interface betw een these tw o layers contains an electric field.
When light hits this junction, some of the photons are absorbed in the region of the junction. If the photons have enough energy, the electrons w ill overcome the electric field at the junction, to freely move through silicon atoms in the cell and into an external circuit.
In the circuit , they w ill be directed to flow in one direction, therefore creating current. Refer to section 2.
Other specifications from Copex the manufacturer of the solar panel also include: M ax. Pow er 0. System Voltage V DC The major selection criterion w as the type of the solar cell; how ever, size w as also another criterion.
This w as because the cell had to be compatible congruent w ith the color filters and other experimental components.
Such as: opacity, thickness, material density, etc…. How ever, I have managed to acquire five chromatic filter plastic sheets w ith similar, if not identical, physical characteristics.
And if there is low er resistance, more current is allow ed to flow through the circuit. The measured data w ith this method may be highly inaccurate. How ever, as I am focusing on the comparison of different spectral responses, the deviation from the absolute accuracy may not affect the comparison appreciably. Every filter had an effect on the intensity of t he light that strikes the surface of the solar panel. In order to find this plane, I had to research and collect data from several resources.
Data for maximum irradiance plane of each month is presented in table 2. This w as done because the country Ethiopia at w hich t he experiment w as done is located in the northern hemisphere. This w ould have avoided any imbalance in light transmission through different medium s. Sticking the filters on the solar panel frame helped to protect the solar panel surface from the residue of the sticking material.
Using this type of chromatic filter has some draw backs. Do not touch terminals. Be sure to safely connect and disconnect all components before and after the experiment, respectively.
Opto-electronic characterization of third-generation solar cells
Do this for all color filters. The follow ing charts generated by using M icrosoft Excel are visual representations of data from table 2. This is because it incorporates all the visible spectrum photons w ith different w avelengths and energy. M oreover, w hen w e see the readings produced from spectral components, it is evident that each component produces different readings of current and voltage. This happens because photons of different w avelengths possess different absorption characteristics.
These free flowing electrons escape through the low er part of the silicon layer and are directed by the potential energy to create current on external circuit. From Chart 1. Particularly the values collected by using the yellow and red filters do not follow the approximately linear trend.
The Physics of Solar Cells - Nelson
This variation maybe in part due to t he difference of intensity of light allow ed through by each filter please see intensity values recorded in table 2. An increase in the intensity of the incident beam keeping the frequency fixed 6 increases the magnitude of the photoelectric current. Therefore, to analyze the data effectively, the intensity of light for each color should be equal. To do that, I have devised a w ay that w ill enable me to simulate uniform intensity for all colors.
Then all recorded currents and Voltages readings w ere recalculated proportionally as per this selected intensity excitation for all colors. Below is the sample calculation for simulated voltage and current : For the green filter, the intensity of light that passed t hrough w as lx.
They work by placing an IB level in the bandgap that introduces a parallel excitation channel, allowing the sequential-two-photon-absorption STPA of sub-bandgap energy photons.
A number of practical implementations based on well-established semiconductor nanostructure fabrication technologies, including quantum dots 4 , and superlattices 5 have been reported. However, the short IB lifetime 6 means they also induce high levels of Shockley-Read-Hall interband recombination 7 that lower the cell voltage.
This QR approach Fig. The upper one intermediate band, IB is optically coupled only to the valence band VB and the lower one Ratchet band, RB is optically coupled only to the conduction band CB.
A rapid irreversible scattering process links the two, so their carrier populations are characterised by the same quasi-Fermi level.
Both are significantly better than the corresponding SQ limits. It achieves this by having two reversible optically allowed transitions denoted by the green arrow VB to intermediate band IB and the red arrow ratchet band RB to CB that are separated by an irreversible IB to RB ratchet transition grey arrow to the right.
A QW superlattice provides the ratchet, as photoelectrons cascade to the right down a series of confined electron states. The device is designed so that the lowest energy interband transition pumps carriers into states at the left hand end of the ratchet, and an intersubband transition, red arrow is required to lift them out or the trapped state at the right hand end of the ratchet to contribute to the photocurrent Full size image Our implementation Fig.
A test device was designed in order to isolate the photocurrent contribution of the STPA channel experimentally. The QCL beam generated no detectable single photon photocurrent, whereas the supercontinuum beam generated a photo current I—V curve with a pronounced low-current plateau in the 0.
In common with IB cell devices based on semiconductor heterostructures the electronic transport in our device is temperature sensitive and so the STPA measurements must be done in a way that avoids artefacts due to sample heating. The fact that this has been achieved can be checked by verifying that the STPA signal is independent of the modulation frequencies. One of the unique aspects of the present work is that we used a frequency mixing circuit to drive a third lock-in amplifier at a frequency corresponding to the difference between the modulation frequencies of the two laser beams.
This is done in order to isolate the fast contribution to the photocurrent that originates from the STPA excitation process. In the lower-noise, mechanically chopped experimental configuration, the frequency mixing was achieved with a custom made digital electronic circuit.
However, we also checked that the signal was unchanged when we took the experiment to the highest frequency available.
This gave a STPA signal that was the same to within experimental error as the much slower mechanically chopped experiment.The forward injection current is unchanged in our example.
While in the following we focus on organic solar cells, the characterization techniques discussed here are not restricted to them but can also be applied to other devices as quantum dots or perovskite solar cells.
The charge transport, however, is less efficient leading to a low fill-factor. Developing a physical understanding of mechanisms governing the operation of third-generation solar cells is much more demanding than for silicon solar cells. Parameter correlation is minimized due to the combination of various techniques. Refer to Temperature change of the solar panel section in the Evaluation unit 2 Another reasonable explanation could be that t he band gap of the poly-crystalline solar cell is narrow.
All other devices are derived from this base device. Photo-oxidation of single molecules during degradation can also lead to doping [ 19 ]. Devices with large active area and distributed series resistance may be calculated with a 2D plus 1D approach [ 25 ].
The holes are extracted from the In0.