23 September 2016 Broadband-sensitive upconverters co-doped with Er3+ and Ni2+ for crystalline silicon solar cells
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We have demonstrated broadband sensitization of Er3+-doped upconverters coupled with crystalline silicon (c-Si) solar cells by introducing Ni2+ co-dopants into ABO3-type perovskite host materials such as La(Ga,Sc,In)O3 and CaZrO3. The Ni2+ sensitizers absorb 1.1−1.45 μm photons, which are not absorbed by either c-Si or Er3+, and transfer the energies to the Er3+ emitters. Thus, 1.1−1.45 μm photons are also upconverted to 0.98 μm photons, in addition to 1.45−1.6 μm photons that are directly absorbed by the Er3+. To compensate the charge imbalance caused by introducing divalent Ni2+ ions into the trivalent (Ga3+, Sc3+, and In3+) and tetravalent (Zr4+) sites, Nb5+ co-dopants were incorporated. Similarly, codoping with monovalent ions (Li+, Na+, K+) notably enhanced the upconversion emission when the Ca2+ sites were substituted with the Er3+ ions. These broadband-sensitive upconverters overcome the shortcoming of conventional Er3+- doped upconverters that only a small portion of the solar spectrum at around 1.55 μm is utilized. If all the photons in the Er3+ absorption band ranging from 1.45 μm to 1.6 μm were perfectly upconverted, the improvement in the short-circuit current density (JSC) would be 1.9 mA/cm2 under the AM1.5G 1 sun solar illumination. The additional improvement for the broadband-sensitive upconverters developed here could be as high as 4.1 mA/cm2 by utilizing 1.1−1.45 μm photons, thus totally 6.1 mA/cm2. This corresponds to a significant gain in conversion efficiency (η) by 3.8% for c-Si solar cells with JSC = 40 mA/cm2 and η = 25%. The architecture of the broadband sensitization opens the door toward the concept of the third-generation solar cells with high conversion efficiency and low cost.
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Yasuhiko Takeda, Hom Nath Luitel, Shintaro Mizuno, Toshihiko Tani, "Broadband-sensitive upconverters co-doped with Er3+ and Ni2+ for crystalline silicon solar cells", Proc. SPIE 9937, Next Generation Technologies for Solar Energy Conversion VII, 99370E (23 September 2016); doi: 10.1117/12.2235502; https://doi.org/10.1117/12.2235502

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