DSSC and TF Poly-Si DSSC and TF Poly-Si Solar CellsSolar Cells

Dye-sensitized TiODye-sensitized TiO22 and thin film poly- and thin film poly-silicon solar cells: fabrication and silicon solar cells: fabrication and

measurements of photomeasurements of photon-to-electron n-to-electron conversion efficiencies using LabViewconversion efficiencies using LabView

National Nano Device Laboratory National Nano Device Laboratory Tainan Science ParkTainan Science Park

Taiwan Tech Trek (TTT) 2006 Interns:Taiwan Tech Trek (TTT) 2006 Interns:

Eric ChangEric ChangDepartment of Electrical Engineering and Computer SciencesDepartment of Electrical Engineering and Computer SciencesUniversity of California at BerkeleyUniversity of California at Berkeley

Kevin Chen Ying ChangKevin Chen Ying ChangDepartment of Electrical and Computer EngineeringDepartment of Electrical and Computer EngineeringUniversity of California at San DiegoUniversity of California at San Diego

Yu-Kai (Kevin) SuYu-Kai (Kevin) SuDepartment of Biomedical EngineeringDepartment of Biomedical EngineeringWashington University in St. LouisWashington University in St. Louis

The Clean RoomThe Clean Room Different levels - NDL Different levels - NDL

Tainan is level 10,000 per Tainan is level 10,000 per cubic feetcubic feet

Requires standard Requires standard uniformsuniforms For our clean room, we For our clean room, we

have to have specialized have to have specialized hats, gloves, jackets, hats, gloves, jackets, shoes, and mouth covers shoes, and mouth covers

Temperature, pressure, Temperature, pressure, and humidity are and humidity are constantly monitored so constantly monitored so room condition can be room condition can be kept at an optimal levelkept at an optimal level

Standard Lab Clothing

The Equipments and TechnologyThe Equipments and Technology

Wet benchWet bench Consists of four different Consists of four different

chemical solutions to eliminate chemical solutions to eliminate extra foreign particlesextra foreign particles

PECVD (Plasma Enhanced) PECVD (Plasma Enhanced) - produces organic thin film - produces organic thin film by growing silicon by growing silicon dioxide/poly-silicondioxide/poly-silicon

Furnace is LPCVD (Low Furnace is LPCVD (Low Pressure) – same function Pressure) – same function as PECVD requiring longer as PECVD requiring longer time for processing but better time for processing but better qualityquality Wet Bench

PhotolithographyPhotolithography Includes following Includes following

processes in order: priming, processes in order: priming, putting on photo resist (PR), putting on photo resist (PR), pre-baking, UV exposure pre-baking, UV exposure with mask, and then hard with mask, and then hard bakebake Exposure - uses a mask to Exposure - uses a mask to

allow entrance of UV light to allow entrance of UV light to hit target wafer, which causes hit target wafer, which causes chemical reaction with the PRchemical reaction with the PR

Area uses yellow light so PR Area uses yellow light so PR is not damagedis not damaged

The Equipments and Technology The Equipments and Technology (Continued)(Continued)

Photolithography

PR spin coated onto wafer PR spin coated onto wafer (manually or automatically)(manually or automatically)

Track (automatic) – Track (automatic) – Can perform all steps Can perform all steps

necessary for coating the necessary for coating the wafer using an automated wafer using an automated computer system computer system

Spin Coater (manual)Spin Coater (manual) Choose desired size of targetChoose desired size of target Manually test optimal Manually test optimal

parameters parameters (RPM/time/position)(RPM/time/position)

The Equipments and Technology The Equipments and Technology (Continued)(Continued)

Spin Coater

Spin CoatingSpin Coating

Main purpose: to achieve an even surfaceMain purpose: to achieve an even surface

Side View of an Uneven Side View of an Uneven SurfaceSurface

slide

Side View of an Even SurfaceSide View of an Even Surface

slide

Spin Coating DemonstrationSpin Coating Demonstration

Thermal Evaporator and Thermal Evaporator and Sputter - both coat thin film Sputter - both coat thin film of metal on the target wafer of metal on the target wafer

Thermal evaporator – Thermal evaporator – evaporated metal on evaporated metal on bottom hits wafer on top, bottom hits wafer on top, then molten metal then molten metal gradually spreads evenly gradually spreads evenly from center of wafer to coat from center of wafer to coat surfacesurface

Sputter – molten metal on Sputter – molten metal on top rains down droplets at top rains down droplets at numerous positions to coat numerous positions to coat the wafer on the bottomthe wafer on the bottom

The Equipments and Technology The Equipments and Technology (Continued)(Continued)

Sputter

The ICP and RIE are The ICP and RIE are both machines that both machines that are used for etchingare used for etching ICP is better since it ICP is better since it

can etch out the whole can etch out the whole target wafer while the target wafer while the RIE cannotRIE cannot

Etchant is very Etchant is very corrosive and corrosive and dangerous, so dangerous, so protective gear is protective gear is requiredrequired

The Equipments and Technology The Equipments and Technology (Continued)(Continued)

Protective Mask

AFM – scans out 3D image of target’s surface AFM – scans out 3D image of target’s surface Nano-scale probe vibrates with a certain frequency Nano-scale probe vibrates with a certain frequency

at a synchronized distance away from the target at a synchronized distance away from the target Vibration changes can be detected by a light that is Vibration changes can be detected by a light that is

reflected upon it, which gives data for imagereflected upon it, which gives data for image Probe stationProbe station

Uses microscope and nano-scale probe to make Uses microscope and nano-scale probe to make contact with different shapes of arrays on targetcontact with different shapes of arrays on target

Probe station is utilized for contact with Probe station is utilized for contact with conductive materials, while AFM targets regular conductive materials, while AFM targets regular surfaces surfaces

The Equipments and Technology The Equipments and Technology (Continued)(Continued)

The MaskThe Mask

The design and pattern The design and pattern of the mask - of the mask - developed through developed through AutoCad, then sent to AutoCad, then sent to specific company for specific company for productionproduction

Normal mask is created Normal mask is created with glass and with glass and Chromium (1-2 months Chromium (1-2 months for completion)for completion) Due to limited time, Due to limited time,

replaced the materials replaced the materials with plastic and chalk, with plastic and chalk, (only an overnight (only an overnight process)process) Masks

Mask AligningMask Aligning

Some Measuring EquipmentsSome Measuring Equipments

Some Measuring EquipmentsSome Measuring Equipments

0.2 mL HAc (hydrogen acetate) in 100 mL DI water

TiO2: 1.35±0.05 g with 40 drops of acetic acid

30303020Time (second)

110012001300500RPM

4321

Finding the Optimal RPM and TimeFinding the Optimal RPM and Time

Table 1: 70 Drops of Acetic Acid

3011007H

3011007G

Less drops, not as evenly distributed3011007F

Less TiO2 at the corners compared to D309007E

not drops, painted on (corners)309007D

3010007C

More drops at corners3011007B

3011007A

CommentTime (second)RPM

Table 2: 80 Drops of Acetic Acid

407008E

108008D

207008C

Not evenly spread309008B

3010008A

CommentTime (second)RPM

SurfactantSurfactant

Triton X 100

Table 3:2 g TIO2 {60, 70, 80} drops Triton X 100 (surfactant)

307008VC

308007XC

309007XB

3012006XB

Thicker than 7A, more bubbles3011006XA

Good, with little bubbles309007XA

CommentTime (second)RPM

SurfactantSurfactant

Fabrication of DSSCFabrication of DSSC

Upper Electrode (1)Upper Electrode (1) Spin-coatingSpin-coating

PR: AZ 5214PR: AZ 5214 Step 1: 500 RPM for 5 sStep 1: 500 RPM for 5 s Step 2: 3000 RPM for 30 sStep 2: 3000 RPM for 30 s

Soft bakeSoft bake 90°C, 30 s90°C, 30 s

ExposureExposure Plastic mask of our designPlastic mask of our design Duration: 4 sDuration: 4 s

Fabrication of DSSCFabrication of DSSC

Upper Electrode (2)Upper Electrode (2) Reverse BakeReverse Bake

110°C, 120 s110°C, 120 s

Reverse, flood Exposure (without mask)Reverse, flood Exposure (without mask) 15 s15 s

DevelopDevelop AZ 300 developer for about 30 sAZ 300 developer for about 30 s

Hard BakeHard Bake 100°C, 60 s100°C, 60 s

In order to make the photoresist negative:In order to make the photoresist negative:

REVERSE BAKEREVERSE BAKE

ANDAND

REVERSE FLOOD EXPOSUREREVERSE FLOOD EXPOSURE

Fabrication of DSSCFabrication of DSSC

SpacersSpacers Spin-coatingSpin-coating

PR: Su8PR: Su8 Step 1: 500 RPM for 5 sStep 1: 500 RPM for 5 s Step 2: 3000 RPM for 30 sStep 2: 3000 RPM for 30 s

Soft bakeSoft bake 90°C, 30 s90°C, 30 s

ExposureExposure Plastic mask of our designPlastic mask of our design Duration: 15 sDuration: 15 s

Fabrication of DSSCFabrication of DSSC

Spacers

No reverse bake or reverse flood exposure

DevelopDevelop AZ 300 developer for about 30 sAZ 300 developer for about 30 s

Hard BakeHard Bake 100°C, 60 s100°C, 60 s

Fabrication of DSSCFabrication of DSSCFinal steps to putting together our DSSC cell:

Put on electrolytes

Place the ITO glass carefully on top of the side with the electrolytes

Hold the ITO glass in place with something

DSSCDSSCHow It Works and How to Test ItHow It Works and How to Test It

injection

regeneration

recapture

hopping

Electron Transfer ProcessElectron Transfer Process

1. conducting F-doped SnO2-coated glass

2. compactTiO2 layer

3. dye-sensitized heterojunction4. gold electrode

Avoids direct contact between the HTM layer and the SnO2, which would cause short circuit

Studying Photovoltaic PerformanceStudying Photovoltaic Performance

Thin-Film Poly-SiliconThin-Film Poly-Silicon

Glass

Bottom electrode ITO 300nm

Induced metal layer Al 250nm

Amorphous Si a-Si 250nm

Induce crystal: 5000 1hr

Al

poly-Si 250nm

Remove Al layer

by wet etching

Amorphous Si

a-Si 4750nm

Anneal at 5000C for 1hr

poly-Si 5000nm

CloseupCloseupA Detailed Look at Our A Detailed Look at Our

ExperimentsExperiments

Photoresist RemainsPhotoresist Remains50x 100x

200x 600x

TiOTiO2250x 100x

200x

TIO2

electrode

]

good contact

LabVIEW PortionLabVIEW PortionMeasurements & ResultsMeasurements & Results

LabVIEW PortionLabVIEW Portion

LabVIEW PortionLabVIEW Portion

LabVIEW PortionLabVIEW Portion

VM

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Time

Voltage

LabVIEW PortionLabVIEW Portion

I1

-5.00E-04

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

3.00E-03

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Time

Current

The ENDThe END