Presented to: Presented by: S. K. Chaudhary Educational Trust’s Shankara Institute of Technology Kukas, Jaipur (Rajasthan) PRESENTATION ON INTERMEDIATE BAND QUANTUM DOT SOLAR CELL Presented to: Mr. Rajesh Kanwadia Ms. Shweta Agarwal (Sr. Lecturer, Seminar Incharge) Presented by: VINEET KUMAR Electronics & communication Engg. B.Tech IV Year(VIIIth Sem)

CONTENTS Photovoltaic Conventional solar cell Introduction Working Limitations Energy bands in solids Intermediate band solar cell Quantum dot Intermediate band quantum dot solar cell Construction Advantages Applications

Introduction to Photovoltaic Generations of voltage from photons Light energy ( photons) are converted into electrical energy ( voltage). This conversion is called “ photovoltaic effect”.

Photovoltaic Generations First generation: silicon wafer-based solar cells Second generation: thin-film deposits of semiconductors Third generation: photo-electrochemical cells

Solar Cell The solar cell (or photovoltaic cell) is a device that converts light energy into electrical energy. Fundamentally, the device needs to fulfill only two functions: 1. Photo-generation of charge carriers (electrons and holes) in a light-absorbing material. 2. Separation of the charge carriers to a conductive contact that will transmit the electricity.

Intermediate band solar cell The intermediate band (IB) is an electronic band located within the semiconductor band gap, separated from the conduction and the valence band by a null density of states. Intermediate band solar cells (IBSCs) are photovoltaic devices. Used to exploit the energy of below band gap energy photons.

ASSUMPTIONS Only radiation recombination One electron-hole pair per photon Constant quasi-Fermi levels No high energy photons in low energy processes Maximum concentration of solar radiation

Intermediate band Requirements Higher photocurrent Higher efficiency arising from absorption of 2 sub-band gap photons to create one electron-hole pair. High voltage V=(EFCB - EFVB)/q V~Eg for main semiconductor Essential for operation 3 quasi-Fermi levels IB “disconnected” from emitters Need IB half-filled with electrons Non-overlapping absorption coefficients

How can we introduce these intermediate energy levels in the band gap? Answer “Introduce Quantum Dots”

Quantum Dot A quantum dot is a portion of matter (e.g., semiconductor) whose excitons are confined in all three spatial dimensions. Quantum dots have properties combined between Those of bulk semiconductors Those of atoms

Physical structure The structure is as follow :

Quantum Dot : Types

Operational principles of IBSC Incoming photons to base layer can cause three different transitions between valance band (VB), conduction band (CB) and IB depending on their energy: VB→CB, if the photon energy is greater then ECV. VB→IB, if the photon energy is greater then EVI IB→CB, if the photon energy is greater then ECI.

Salient characteristics of QDs for IBSC Dot sized shape, composition Dot spacing Dot regularity Materials Doping

ADVANTAGES Higher Efficiency. Balance between the two factors (I) Cost (II) Efficiency

APPLICATIONS Photovoltaic devices: solar cells Light emitting diodes: LEDs Quantum computation Flat-panel displays Memory elements Photodetectors Lasers

What limits performance of these QD IBSC? Low open-circuit voltage Low currents Cost

Conclusions QD SL cells show photo responses extended to longer wavelengths than GaAs control cells, demonstrating current generation from the absorption of sub-band gap photons. IBSC theoretically offers a way to significantly increase cell efficiency compared to that of a single-junction solar cell.

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