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Spatial Architecture Impact in Mediation Open Circuit Voltage Control of Quantum Solar Cell Recovery Systems INTERNATIONAL JOURNAL OF ENERGY and ENVIRONMENT Volume 12, 2018 Spatial Architecture Impact in Mediation Open Circuit Voltage Control of Quantum Solar Cell Recovery Systems Moustafa Osman Mohammed can confine electrons (quantum confinement) in quantum solar Abstract—These photocurrent generations are influencing ultra- cell systems [1]. When the size of a QD approaches the size of high efficiency solar cells based on self-assembled quantum dot the material's exciton Bohr radius, quantum confinements, the (QD) nanostructures. Nanocrystal quantum dots (QD) provide a effect becomes prominent and electron energy levels can no great enhancement toward solar cell efficiencies through the use of longer be treated as continuous band, they must be treated as quantum confinement to tune absorbance across the solar spectrum enabled multi-exciton generation. Based on theoretical predictions, discrete energy levels [2]. Hence, QD can be considered as an QD solar cells have potential for efficiencies greater than 50%. In artificial molecule with energy gap and energy levels spacing solar cell devices, an intermediate band formed by the electron dependent on its size (radius). The energy band gap increases levels in quantum dot systems. Spatial architecture is exploring with a decrease in size of the quantum dot. As the size of a QD how can solar cell integrate to produce not only high open circuit increases its absorption peak is red shifted due to shrinkage of voltages (> 1.7 eV) but also large short-circuit currents due to the its band gap of QDs [3]. The adjustable band gaps of quantum efficient absorption of sub band gap photons. In the proposed QD system, the structure allows barrier material to absorb wavelengths dots allow the construction of nanostructured solar cell that is below 700 nm while multi-photon processes in the used quantum able to harvest more of the solar spectrum [4]. QDs have large dots to absorb wavelengths up to 2 µm. The structure and material intrinsic dipole moments, which may lead to rapid charge compositions are flexible to tune the energy bandgap of the barrier separation. Quantum dots have been found to emit up to three material and quantum dot to their respective optimum values. This electrons per photon due to multiple exciton generation structure is expected to outperform single or multi-junction solar (MEG), as opposed to only one for standard crystalline silicon cells in terms of energy virtual conversion efficiency and cost. A key milestone towards achieving the claimed high-efficiency solar solar cell. Theoretically, this could boost solar power cell device is flexibly tuning the energy bandgap between the efficiency from 20 % to as high as 65 % [5]. barrier material and QD according to the designed limits. Despite Initially, there are main important parameters can be this remarkable potential for high photocurrent generation, the characterized to quantify the performance of a photovoltaic achievable open-circuit voltage (V ) is fundamentally limited due oc cell. These are the open-circuit voltage (Voc), the short circuit to non-radiative recombination processes in QD solar cells. current (Isc), and the fill factor (F F). However, the fill factor is Comparing experimental Voc variation with the theoretical upper- limit obtained from one diode modeling of the cells with different also a function of Voc and Isc. Therefore, these focus on two bandgap (Eg), the proposed architecture is clearly demonstrated parameters that are the key factors for determining the cell’s that there is a tremendous opportunity for improvement of Voc to power conversion efficiency. In the regular conditions, each values greater than 1 V by using smaller QDs through QD solar photon incident on the cell with energy greater than the band cells confined states with other nano operation systems. gap will provide energy to produce an electron flowing in the external intermediate circuit. The false or fill factor is Keywords—Nanotechnology, Photovoltaic Solar Cell, Quantum determined from the maximum area of the I-V characteristics Systems, Renewable Energy, Environmental Modeling, under illumination voltage meter with other preliminary circuit current and open circuit voltage, or comply with fundamental I. INTRODUCTION given equation to[6]: IGNIFICANT documents are focus on diagnoses function of (1) S nanocrystal quantum Systems. Quantum Systems are a complete class of semiconductors quantum dots, which are nanocrystals, composed of periodic groups of II-VI, III-V, or where, Vmp and Imp are the majority operating point that will IV-VI of the periodic table, such as CdS, CdSe, CdTe, collect and charge the power output. While, the initial energy CdS@ZnS, CdSe@ZnS, CdSeTe@ZnS. These QDs provide conversion efficiency is given by [7]: excellent fluorescence properties that have been applied in biosensing and intracellular or in vivo imaging materials and (2) Moustafa Osman Mohammed is with the Egyptian Environmental Affairs where Pin is the input power. Agency (EEAA); (e-mail: moustafa_o@ yahoo.com). ISSN: 2308-1007 58 INTERNATIONAL JOURNAL OF ENERGY and ENVIRONMENT Volume 12, 2018 The main objective is to give an introductory coverage of a B. QD Nanotechnology in Solar Cell sophisticated quantum system. Construction model depends on The rays from the sun consist of different energy levels. the physics, designs, structures, and some growth/synthesis Solar spectrum has the photons with the energy level from techniques of quantum solar cell systems. The comprehensive 0.5ev to 3.5ev. So, by the use of the silicon in the solar cell description of spatial architectures of QD solar cells systems most of the photons with the energy level of above 1.14ev will (e.g., Schottky cell, layer of p-i-n configuration, depleted be wasted as the heat. The practice solution is used to heterojunction, and quantum dots sensitized solar cell) provide overcome this problem with Quantum dot as a nano material an innovation nanotechnology to sustainable production of used in the solar cell to increase the efficiency of the solar cell clean energy and reduce greenhouse gases (GHG) [8], [9]. [16]. Quantum dot is a zero dimensional system where electron motion is confined in three dimensions. Therefore, a II. QUANTUM SOLAR CELL SYSTEMS quantum dot possess atomic like density of states that is Current solar cells systems cannot convert all the incoming described mathematically by a delta function δ (EEc/v) . light into usable energy because of the light back out escape of Unlike conventional materials, one photon generates just the cell into the air reflection. Additionally, sunlight has one electron; quantum dots have the potential to convert high- spectrum within a variety of colors and the cell might be more energy pho-tons into multiple electrons. Quantum dots behave efficient at converting bluish light while being less efficient at as the same way, but produce three electrons for every photon converting reddish light. While the light lower energy passes of sunlight that hits the dots. Electron is displaced from the through the cell unused, a higher energy light does excite valance band into the conduction band. These dots have more electrons to the conduction band, and a partial of energy sunlight wave spectrums for improving conversion efficiency beyond the band gap energy is converted as heat. The solar as high as 65% percent. Another area in which quantum dots cell systems are organized to capture these excited electrons could be used to improve efficiency is, so – called a hot carrier aren’t captured and redirected its charge to the electrode, they cells. Typically the extra energy is transferred by a photon as will spontaneously recombine to create differential voltage heat, but with a hot carrier cells the extra energy from the current that produce energy from heat or light [10]. photons result in higher-energy electrons in turn captured to Solar cell is also known as the photovoltaic cell which lead to higher voltage efficiency [17], [18]. converts the solar energy from the sun into electrical energy C. Improving Solar Cell Efficiency with QD based on the principle of photovoltaic effect. Solar cell is the building blocks of photovoltaic effect. The operation of One of the starting points for the increase of the con-version photovoltaic cell requires two functions-one is photo efficiency of solar cells is the use of semiconductor quantum generation of charge carrier in a light absorbing material and dots (QD). By means of quantum dots, the band gaps can be the second is the separation of charge carrier to a conductive adjusted specifically to convert also longer- wave light and contact that will transmit the electricity [11].This is called as thus increase the efficiency of the solar cells. These so called the photovoltaic effect. The photovoltaic cell system was first quantum dot solar cells are, at present still subject, to basic experimentally said by Edmond Becquerel in 1839. The first research. As material systems, QD solar cells, III/V practical photovoltaic cell system was demonstrated in the semiconductors and other material compositions such as Si/Ge year 1954. Later the model of the quantum solar cell systems or Si/Be Te/Se are considered as potential advantages of these was developed and it is used mostly in the solar cell silicon as Si/Ge QD solar cells for: the light absorbing material to convert solar energy into clean 1) Higher light energy absorption in particular to the electrical energy [12]. infra-red spectral region, 2) Compatibility with standard conventional silicon solar cell production (in contrast to III/V semiconductors), A. Conventional Work of a Solar Cell 3) Increasing of photo current at higher temperatures, Solar cell converts the solar energy into electrical energy. 4) Improving radiation hardness in comparing to The sun rays contain certain energy level and some of the conventional silicon solar cells. photons in the sun rays are absorbed by the light absorbing The transport of electrons across the particle net-work is the material which is present in the solar cell.
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