Yazar "Gratzel, Michael" seçeneğine göre listele

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    Hydrothermally processed CuCrO2 nanoparticles as an inorganic hole transporting material for low-cost perovskite solar cells with superior stability
    (Royal Soc Chemistry, 2018) Akın, Seçkin; Liu, Yuhang; Dar, M. İbrahim; Zakeeruddin, Shaik M.; Gratzel, Michael; Turan, Servet; Sönmezoğlu, Savaş
    Despite the impressive photovoltaic performances of perovskite solar cells (PSCs) with a power conversion efficiency (PCE) beyond 22%, intensive studies are still required to overcome ongoing issues such as cost, stability, and hysteresis. Here, for the first time, we report a cesium-containing triple-cation mixed-halide perovskite solar cell (n-i-p structure) by using hydrothermally synthesized inorganic CuCrO2 (CCO) delafossite nanoparticles as a hole transporting material (HTM). After optimization of the concentration, a fully homogeneous and completely covered CCO layer that facilitates fast carrier extraction and collection was obtained on the surface of the perovskite. Our CCO-based cells achieved the best PCE of 16.7% (average 16.04 +/- 0.40) with negligible hysteresis. More importantly, it was found that our cells showed a significant improvement in stability in ambient air compared with Spiro-OMeTAD HTM-based cells. After 60 days of storage in air without encapsulation, PCE remained at similar to 83% of the initial value with the CCO-based cells, whereas it decreased to similar to 24% of the initial value with devices based on the Spiro-OMeTAD HTM. Furthermore, cost estimation results indicated that the current prospect of CCO has an affordable cost/device ratio (similar to 180-fold cheaper than Spiro-OMeTAD). This work not only reveals the importance of air-stable inorganic HTMs, but also provides a low-cost HTM for highly efficient and stable PSCs.
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    Power output stabilizing feature in perovskite solar cells at operating condition: Selective contact-dependent charge recombination dynamics
    (Elsevier Science Bv, 2019) Kim, Hui-Seon; Seo, Ji-Youn; Akın, Seçkin; Simon, Elfriede; Fleischer, Maximilian; Zakeeruddin, Shaik M.; Gratzel, Michael
    Stabilized power output at maximum power point (mpp) has been considered as one of the most reliable parameters as it provides a key performance indicator for perovskite solar cells (PSCs) revealing the operational stability of the photovoltaic device. Here, we show the effect of selective contact on the power output change under mpp tracking, which closely correlates with the charge recombination dynamics with a time scale of minutes. The normal n-i-p cell architecture comprising cp-TiO2/mp-TiO2/perovskite/spiro-MeOTAD (doped by either Li-TFSI or Zn-TFSI2) and the inverted p-i-n structure, NiOx/perovskite/PCBM, are examined to investigate the specific effect of the nature of the interface on operational stability. The normal structure with Li-TFSI shows a gradual performance decrease at mpp owing to the enhanced recombination at the interface between the perovskite and the spiro-MeOTAD, becoming the dominant recombination process, although the bulk-related recombination is suppressed. On the other hand, the inverted structure demonstrates an improved photocurrent at mpp due to the effectively suppressed recombination both in bulk and at the interface. Remarkably, the deteriorating performance of the normal structure with Li-TFSI at mpp is successfully avoided by replacing Li-TFSI with Zn-TFSI2, leading even to an increased power output with stable performance at mpp.