CHE 310 Lecture 10: CHE310SolarEnergy

47 views5 pages

ochredeer895

26 Feb 2017

School

Stony Brook University

Department

Chemistry

Course

CHE 310

Professor

Katherine Aubrecht

For unlimited access to Class Notes, a Class+ subscription is required.

Document Summary

Band gap = the energy gap between the top of the valence band and the bottom of the conduction band; determines the minimum amount of energy needed to convert light into energy. Valence band = electrons are localized; level is filled. Conduction band = electrons can move freely; level is empty. Bands are created when an infinite number of atomic orbitals are combined. The size of the band gap affects the ability of electrons to jump between the conduction and valence bands. Smaller gap electrons can move more easily. Semiconductor = solids with electrical properties between metlas and insulators. Must have a small band gap so electrons can be promoted from a valence band to the conduction band using thermal energy or by absorbing a photon with more energy than the band gap. Creates a hole in the valence band and an extra mobile electron in the conduction band.

Related Questions

I have already attempted most of these questions; I just wantedsomeone else's opinion to see if my answers are right or wrong andtell me why if its wrong. Thanks:

Q1:

A doped semiconductor is dipped into a solution of electrolyte.The electrolyte solution contains a redox species with a mid-gapelectrode potential. After absorbing a photon in excess of itsbandgap energy, the photoexcited electron in the conduction band(CB) of a semiconductor moves spontaneously to the interfacebetween the semiconductor and the liquid electrolyte. The hole inthe valence band moves spontaneously away from the solid/liquidinterface and into the bulk of the semiconductor. What is thecorrect statement about the doping of this semiconductor?
a. n-doped, because there is an electric fieldgenerated at the interface that drives the electrons to thesolid/liquid interface.
b. n-doped, since it has an excess of electronsthe e- in the CB wants to escape.
c. p-doped, because it has an excess of negativecharges in the semiconductor at the solid/liquid interface thatattract the electrons.
d. p-doped, because there is an electric fieldthat drives the electrons to the solid/liquid interface
e. n-doped, because it has an excess of positivecharges in the semiconductor at the solid/liquid interface, whichattract the photoexcited electrons

Q2:

Calculate the maximum output voltage (a.k.a. cell potential) fora dye-sensitized solar cell constructed from n-type SnO₂(E_CB = E_Fermi = +0.3V) usingFe³⁺/Fe²⁺ as the redox mediator. Use AppendixD and assume that all concentrations are standard state.

Q3:

Which of the following is true about Graetzel-type solarcells?

a. Gratzel cells are not asefficient as multilayered dye-sensitized solar cells

b. Low surface area films of TiO2provide optimal binding for dyes

c. Cell voltages are susceptible torecombination from the CB to the redox mediator

d. Light absorption and cell output voltagesare worse than planar dye-sensitized solar cells

e. Band bending occurs in thesemiconductor phase

My answers are:

1. d

2. 0.47

3. e

Synthesis of Copper(I) Oxide Particles with Variable Color:Demonstrating Size-Dependent Optical Properties

Introduction
Cluster based materials exhibit considerable advantages over bulk materials including surface features, electrostatic fields and reactivity that can differ and/or be varied as a function of both composition and cluster size. Nanocrystals formed from semiconductor materials with diameters of 1 â 30 nm are often referred to as quantum dots. Quantum dots are already in commercial use in sensors, LEDS and lasers including those used as readers for HD-DVD and Blu-ray high-definition DVDs. The spectral properties of quantum dots arise from a quantum confinement effect. When an electron in these semiconducting materials is excited into the conduction band a hole is created in the valence band. The physical distance between the location of the excited electron and the hole it came from is called the Bohr exciton radius (rB). In a bulk semiconductor crystal rB is small compared to the overall size of the crystal and the electron can migrate freely through the lattice. However, in the nanoscale quantum dot, rB is close to the diameter of particle and the electron is trapped in molecular orbitals rather than bands of orbitals. The energy spacing of these molecular orbitals depends on the number of atoms and hence the size of the crystal. Consequently, the excitation or absorption energy changes with the size of the quantum dot. As the dot gets bigger the absorption energy moves to lower frequency and the colour of light reflected changes from blue to red.

In this experiment you will synthesise micro- and nanosized copper(I) oxide particles with size-dependent optical properties by reducing alkaline copper(II)âcitrate complex (Benedictâs reagent) with glucose. The Cu2O particles varies from hundreds of nanometers to micrometers depending on concentrations of initial reagents and their colour varies from yellow to dark red, accordingly. Shown below are the electron-half-equations (a, b) and summary redox reaction (c) between copper(II) 25 ions and Î±-hydroxy-ketone group of reducing sugars (e.g., fructose) in open-chain form. Redox reaction is activated by transformation of Î±-hydroxy-ketone group to enediol via keto-enol tautomerization in alkali solutions.
a) Oxidation: R1CH(OH)COR2 + 2 OH â R1COCOR2 + 2 H2O + 2 eâ
b) Reduction: 2Cu(in complex)2+ + 2 OHâ + 2 eâ â Cu2O + H2O
c) Summary: R1CH(OH)COR2 + 2Cu2+ + 4 OHâ â R1COCOR2 + Cu2O + 3H2O

Question1:

Provide a brief summary of three research articles covering Cu₂O semiconductors (cite refs)?

Question2:

In this experiment you use Benedictâs reagent to synthesis copper (I) oxide nanoparticles. Research the scientific literature and provide a brief description of two alternative applications of Benedictâs reagent. (cite refs)?

CHE 310 Lecture 10: CHE310SolarEnergy

Document Summary

Get access

Related Questions