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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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    Inorganic cufeo2 delafossite nanoparticles as effective hole transport materials for highly efficient and long-term stable perovskite solar cells
    (American Chemical Society, 2019) Akın, Seçkin; Sadegh, Faranak; Turan, Servet; Sönmezoğlu, Savaş
    The regular architecture (n-i-p) of perovskite solar cells (PSCs) has attracted increasing interest in the renewable energy field, owing to high certified efficiencies in the recent years. However, there are still serious obstacles of PSCs associated with spiro-OMeTAD hole transport material (HTM), such as (i) prohibitively expensive material cost (∼150−500 $/g) and (ii) operational instability at elevated temperatures and high humidity levels. Herein, we have reported the highly photo, thermal, and moisture-stable and cost-effective PSCs employing inorganic CuFeO2 delafossite nanoparticles as a HTM layer, for the first time. By exhibiting superior hole mobility and additive-free nature, the best-performing cell achieved a power conversion efficiency (PCE) of 15.6% with a negligible hysteresis. Despite exhibiting a lower PCE as compared to the spiroOMeTAD-based control cell (19.1%), nonencapsulated CuFeO2-based cells maintained above 85% of their initial efficiency, while the PCE of control cells dropped to ∼10% under continuous illumination at maximum power point tracking after 1000 h. More importantly, the performance of control cells was quickly degraded at above 70 °C, whereas CuFeO2-based cells, retaining ∼80% of their initial efficiency after 200 h, were highly stable even at 85 °C in ambient air under dark conditions. Besides showing significant improvement in stability against light soaking and thermal stress, CuFeO2-based cells exhibited superior shelf stability even at 80 ± 5% relative humidity and retained over 90% of their initial PCE. Overall, we strongly believe that this study highlights the potential of inorganic HTMs for the commercial deployment of long-term stable and low-cost PSCs.