Questions and Answers
Ternary Compound Nanocrystals for Photovoltaic Devices, IB-2740:
Q1: What is the technology readiness level (TRL)? Have photovoltaic devices already been fabricated and tested with the ternary compound nanocrystals?
A: Berkeley Lab researchers have fabricated a lot of fully functional solar cells of the material in the past. In fact, this has been our way to optimize the material. However, our lab is not specialized in solar cell fabrication and hence, our solar cell fabrication tools do not meet industrial standards. For instance, all cells were tested using a Schottky architecture and not the favorable "depleted heterojunction" lay-out. The researchers would expect the material to perform even better in the latter architecture but this has not been tried, yet. Also, no attempts were made in applying anti-reflective coatings or patterned metal back contacts which, the researchers believe, is routinely applied in industry as well.
Q2: What was the method used to synthesize the nanocrystals?
A: The nanocrystals were synthesized by a colloidal chemistry approach in solution using organic molecules as stabilizers.
Q3: Was a capping agent, such as TOPO or similar, used to prevent aggregation?
A: The capping agent was Oleic acid.
Q4: Have the nanocrystals been used in a photovoltaic cell or full sized panel?
A: Yes. Particles of different sizes and composition were tested as photoactive layers in fully functional solar cells with Schottky-geometry. These cells were fabricated for test purposes, where the unoptimized fabrication procedure did not meet industrial standards. Large solar panels have not been fabricated with this material, yet.
Q5: If the technology has been used in photovoltaic devices, what is the performance (such as open circuit voltage, short circuit current, fill factor and power conversion efficiency) of an individual PV cell?
A: For the unoptimized devices studied, the best performing composition repeatedly showed:
- Open circuit voltage = 0.45 V
- Short circuit current density = 15 mA/cm2
- Fill Factor = 50 %
- Efficiency = 3.3 %.
Q6: What method was used to prepare thin films for the PV cells? Were nanocrystals incorporated into a matrix to make the thin films?
A: The thin films were prepared by subsequent spin-coating of one nanocrystal layer, followed by cross-linking with benzene-1,3-dithiol, followed by the next layer and so forth until the desired thickness had been reached. No matrix was applied.
Q7. Is it possible to make large-area thin films with the nanocrystals?
A: Yes. If spin-coating is not an option for very large substrates, the particles may also be dip-coated or even applied by spraying.
Q8: If known, what is the TRL (Technology Readiness Level)?
A: The researcher did not assign a TRL value, however see the answer to Q1 above.
Q9: The technology description implies that PbSxSe1-x has superior charge transport without reducing responsivity to photon excitation. Is that the case? If so, could we reasonably apply for this TTO grant for use with a photonic detector rather than a solar cell?
A: The material presented has been optimized with respect to the photovoltaic performance. To the researcher's knowledge, attempts to use it in photodetectors have not been undertaken so far. However, due to the similar mode of operation, the researcher would expect it to perform well when applied as the light absorbing material in a photodetector, too. The advantage of the higher generated photocurrent in PbSxSe1-x over comparable PbS nanoparticles holds true and should be equally beneficial for photodetectors. One specific aspect of the responsivity is trapping of minority carriers which is detrimental for solar cells but quite welcome in photodetectors. This difference would have to be tested to be able to say more about the potential of this material for photodetectors.
Q10: Once a company is selected, will Berkeley Lab have some quantity of nanocrystals to provide the selected company? Or will Berkeley Lab have to fabricate the material and transfer it under a Materials Transfer Agreement (MTA)?
A: Some material is available, however, the researcher strongly recommends using a freshly-prepared sample. An MTA will be required for the materials transfer.
Q11: Would Berkeley Lab researchers be able to assist the selected company by providing expertise and answering questions about optimizing device performance?
Q12: Would Berkeley Lab facilities be available for testing nanocrystal solar cell devices or conducting experiments such as analyzing performance as a function of particle ratiometric mixtures?
Irreversible, Low Load Genetic Switches, EJIB-2593:
Q: Is there a published patent application for this technology?
A: Yes. At this link, input the published patent application number 13088288.