Biomedical Engineering Reference
In-Depth Information
different.shortcomings..Man-made.solar.panels.are.designed.to.produce.energy.only,.but.
also.result.in.many.environmental.problems.with.toxic.by-products..Natural.systems.have.
evolved.primarily.for.survival,.so.they.convert.the.electronic.potential.derived.from.the.
sun.into.a.biomass.that.they.can.store,.and.unlike.man-made.solar.devices,.they.are.not.
robust,.static.systems,.but.constantly.regenerate.components.to.maintain.photosynthetic.
function—again,.focusing.on.survival.vs..total.energy.output.
However,.a.new.technological.paradigm.in.the.form.of.biohybrid.systems.is.emerging,.
and.it.holds.the.promise.of.merging.the.longevity.of.man-made.devises,.crafted.by.inten-
tional.design,.with.the.functionality.of.biological.components.perfected.through.millions.
of.years.of.natural.selection.that.are.still.too.intricate.for.us.to.duplicate..Biosolar.is.a.prime.
example.of.one.such.technology.emerging.from.this.recent.philosophy,.and.with.it.we.ask.
ourselves. a. fundamental. question:. Can. we. integrate. the. biological. components. respon-
sible.for.turning.sunlight.into.energy.into.a.man-made.device?.And.in.doing.so,.can.we.
harness.their.functionality.to.produce.an.energy-producing.device.that.does.not.have.the.
environmental.shortcomings.of.conventional.solar.energy?
In.this.chapter,.we.will.discuss.the.engineering.aspects.of.producing.such.a.hybrid.device..
We.will.start.by.briely.comparing.how.different.classes.of.solar-voltaic.devices.operate,.
comparing. the. similarities. and. differences. between. silicon. solid-state,. dye-sensitized.
solar,. and. biosensitized. solar. technologies.. Next,. we. will. describe. in. greater. detail. the.
components. and. physical. considerations. associated. with. the. biohybrid. solar. cell:. the.
structure.and.functions.of.photoactive.proteins,.the.conformation.of.solid-state.substrates,.
and.a.consideration.of.physical.interactions.that.occur.at.the.bio-nanostructure.interfaces..
Finally,.we.will.report.on.engineering.strategies.aimed.at.building.and.maintaining.pro-
tein.adsorption.and.stability.on.a.solid.electrode.
22.2 SolarCellReview:FromSilicontoDyetoProtein
22.2.1 Silicon Solar Cell
Regardless.of.whether.they.are.man-made.or.naturally.occurring,.deriving.and.then.the.
process.of.capitalizing.excited.electrons.via.photonic.means.can.be.broken.down.into.four.
fundamental.elements:
.
1.. Absorption.of.photons
.
2.. Excitation.of.electronic.states
.
3.. Charge.separation.and.transport.through.a.load
.
4.. Returning.of.electrons.to.the.original.donor.materials
Solid-state.silicon-based.photovoltaics.operate.on.manipulating.the.electroenergy.states.
of.semiconductors.by.doping.the.material.with.impurities,.making.it.more.prone.to.accept.
or.donate.electrons..Silicons.doped.with.electron.donors.(i.e.,.phosphorus).are.known.as.
n-type.materials,.while.those.infused.with.electron.acceptors.(boron).are.known.as.p-type.
materials.
By.itself,.an.n-type.doped.silicon.material.can.absorb.sunlight.to.promote.a.stationary.
electron.into.a.delocalized.state.(steps.1.and.2)..However,.the.pathway.of.this.electron.is.
random.and.will.quickly.reill.the.positively.charged.valence.that.was.coproduced.upon.
