@article{KoehnenWagnerLangetal., author = {K{\"o}hnen, Eike and Wagner, Philipp and Lang, Felix and Cruz, Alexandros and Li, Bor and Roß, Marcel and Jošt, Marko and Morales-Vilches, Anna B. and Topič, Marko and Stolterfoht, Martin and Neher, Dieter and Korte, Lars and Rech, Bernd and Schlatmann, Rutger and Stannowski, Bernd and Albrecht, Steve}, title = {27.9\% Efficient Monolithic Perovskite/Silicon Tandem Solar Cells on Industry Compatible Bottom Cells}, series = {Solar RRL}, volume = {5}, journal = {Solar RRL}, number = {7}, publisher = {Wiley}, doi = {10.1002/solr.202100244}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:523-15145}, pages = {8}, abstract = {Monolithic perovskite/silicon tandem solar cells recently surpass the efficiency of silicon single-junction solar cells. Most tandem cells utilize >250 μm thick, planarized float-zone (FZ) silicon, which is not compatible with commercial production using <200 μm thick Czochralski (CZ) silicon. The perovskite/silicon tandem cells based on industrially relevant 100 μm thick CZ-silicon without mechanical planarization are demonstrated. The best power conversion efficiency (PCE) of 27.9\% is only marginally below the 28.2\% reference value obtained on the commonly used front-side polished FZ-Si, which are about three times thicker. With both wafer types showing the same median PCE of 27.8\%, the thin CZ-Si-based devices are preferred for economic reasons. To investigate perspectives for improved current matching and, therefore, further efficiency improvement, optical simulations with planar and textured silicon have been conducted: the perovskite's bandgap needs to be increased by ≈0.02 eV when reducing the silicon thickness from 280 to 100 μm. The need for bandgap enlargement has a strong impact on future tandem developments ensuring photostable compositions with lossless interfaces at bandgaps around or above 1.7 eV.}, language = {en} } @article{KemppainenBagackiScharyetal., author = {Kemppainen, Erno and Bagacki, Rory and Schary, Christian and Bao, Fuxi and Dorbandt, Iris and Janke, Stefan and Emery, Quiterie and Stannowski, Bernd and Schlatmann, Rutger and Calnan, Sonya}, title = {Dynamic Operation of a Heat Exchanger in a Thermally Integrated Photovoltaic Electrolyzer}, series = {Energy Technology}, volume = {11}, journal = {Energy Technology}, number = {2}, doi = {10.1002/ente.202201081}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:523-16903}, abstract = {The outdoor operation of an up-scaled thermally photovoltaic electrolyzer (PV EC), constructed using a heat exchanger (HE) made of low-cost materials, compared to its nonintegrated counterpart to quantify heat transfer and its effects, is studied. Thermal coupling of the PV and EC can reduce the difference between their temperatures, benefitting device performance. Such devices can produce hydrogen at rooftop installations of small-to-medium-sized nonindustrial buildings. The devices are tested outdoors using automated real-time monitoring. Under ≈880 W m-2 peak irradiance, they produced hydrogen at ≈120 and ≈110 mL min-1 rate with and without HE, respectively, corresponding to about 8.5\% and 7.8\% solar-to-hydrogen efficiencies. During about 700 h of testing, the HE is beneficial at over ≈500 W m-2 due to cyclic device operation. Under lower irradiance levels, pumping previously heated electrolyte through the HE increases the PV and reduces the electrolyte temperature, reducing the device performance. The HE increases the cumulative hydrogen production (≈800 L from both devices), so even relatively modest heat transfer rates can improve the PV EC operation. Improving the HE should further increase the benefits, but additional measures may be needed to maximize the hydrogen production.}, subject = {W{\"a}rmeaustauscher}, language = {en} }