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20 The PCB Design Magazine • December 2017 DR. JOHANNES ADAM SOUNDS THE ALARM FOR THERMAL DESIGN doing the simulation, experimenting with trace thickness, prepreg thickness, board thickness, trace structure, and component placement. There is rarely a linear relation between input values and result. Shaughnessy: What's the name of your com- pany? Adam: The company is called ADAM Research. You can reach me directly on the support line. I also am affiliated with another company, Easy- Logix, or Schindler & Schill in Germany, where we cooperate to bring thermal issues and other physics topics into their DFM tool called PCB- Investigator. Shaughnessy: I'm sure EEs will want to learn more about your thermal software. Adam: On my website, they can find a list of features, case studies and more information. Just drop a note and either myself or a distributor will get in personal contact. Shaughnessy: Well, best of luck with your up- coming book, and your quest to educate our in- dustry about thermal issues. Adam: Thank you for the opportunity, Andy. PCBDESIGN When sunlight strikes a typical solar panel, it cre- ates pairs of electrons and positively charged holes. Normally, an electric field is used to separate these charges and produce electrical power, but this ap- proach requires charges that have high mobilities and lifetimes, which makes it hard to develop new photovoltaic materials. An alternative approach for extracting current from solar cells involves exploiting the symmetr y of the repeating structural units that make up crystals. For such semiconductors, light-induced transi - tions of charges to excited states become unbal- anced, which creates a 'shift current' along a spe- cific crystal direction. This shift current propagates rapidly and with less energy loss than a current generated by applying an electric field. But shift currents usually generate insufficient photovoltaic power for practical uses. Now, Masao Nakamura from the RIKEN Center for Emergent Matter Science and colleagues have over - come this shortcoming by using ferroelectric organic molecules that spontane- ously separate their posi- tive and negative charges. Because ferroelectric ma- terials naturally disrupt inversion symmetry, they have potentially large shift currents—particularly when charge separation occurs due to quantum- mechanical differences in the covalent bonds hold - ing a crystal together. The team investigated an organic ferroelectric with strong quantum polarization to explore its shift-current capabilities. Composed of alternately stacked tetrathiafulvalene (TTF) and p-chloranil (CA) aromatic rings, this complex undergoes in - stantaneous charge separation when cooled to around -200 degrees Celsius and is particularly sensitive to sunlight. "Most ferroelectric materials need light with en- ergy in the ultraviolet region to excite carriers over a large band gap," says Nakamura. "With TTF–CA, the band gap is narrow and responds to visible and infra- red light, which is really im- portant for applications like solar cells." When the researchers measured the photovoltaic properties of the organic complex, they were taken aback by the amount of shift current generated—nearly ten times higher than com- parable oxide ferroelectrics. Solar Cells With a Quantum Shift

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