Slide 1Motivation: Existing technologiesExperimental data, Part 1: Bilayer cellsPart 2: Single material & blended cellsPart 3: Anneal & sinterColloidal Semiconductor Nanocrystals, in summary…Questions??REVIEW:“AIR-STABLE ALL-INORGANIC NANOCRYSTAL SOLAR CELLS PROCESSED FROM SOLUTION”I. GUR, N. FROMER, M. GEIER, A.P. ALIVISATOS. SCIENCE, OCT. 2005EE 235 Presentation #1 S. Swisher 3/2/09Motivation: Existing technologiesBroadband absorptionSuperior transport propertiesHigh cost of materials, processing, & installationPotential cost reductionScalable, controlled synthesisProcessed in solutionLow carrier mobilityLimited spectral absorptionEnvironmental stability problemsInorganic bulk solar cells Organic solar cellsExperimental data, Part 1: Bilayer cellsSpin-cast rod shaped CdSe & CdTe NCsStrong photoconductive effect suggests limited free carriers in darkDepletion region with built-in field unlikely mechanism for charge separationRigid band model more accurate than band bendingCarrier extraction by directed diffusion: electrons and holes both go to lower energy states!Part 2: Single material & blended cellsBilayer vs. CdSe or CdTe only, and mixed blendsNo rectification in single material no Schottky contactBlends performed better than single material; implies D-A junction rather than conventional P-NBilayer cell = highest efficiencyVery little confinement along length of rod. Free carriers move throughout NC film.Part 3: Anneal & sinterBest Device:ISC = 13.2mA/cm2VOC = 0.45VFF = 0.49Eff = 2.9%Minimize surface traps by annealing at 400C for 15 minutesIncrease photoconductivity 2 orders of magnitudeNo photo-oxidationColloidal Semiconductor Nanocrystals, in summary…Ultra-thin, solution processed, stable in ambient environmentDiffusion-assisted D-A heterojunctionsSintering enhances performanceKey development toward stable and low-cost solar energy
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