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Neha Arora1 Michael Grätzel1

1, Ecole Polytechnique Federale de Lausanne, Lausanne, , Switzerland

Unceasing demands for the fabrication of low-cost highly efficient light harnessing devices compelled photovoltaic community to investigate newer materials that has eventually led to the evolution of hybrid perovskite solar cells. Primarily due to the enticing optical, excitonic, and electrical properties, organic-inorganic lead perovskites are considered as suitable light absorbing materials for the development of efficient solar cells. Thus far, much of the focus has been on iodide-based perovskite solar cells, which display record efficiencies mostly because of high current densities. In comparison, bromide-based perovskites bring forth higher open-circuit voltage, which could be beneficial for tandem solar cell applications and in driving electrochemical reactions, including water splitting reactions and CO2 reduction. However, extrinsic as well as intrinsic instability of perovskite solar cells has proven to be an invincible bottleneck towards their commercialization. In my presentation, I will discuss the fabrication of formamidinium lead bromide (CH(NH2)2PbBr3) perovskite solar cells yielding photovoltage above 1.5 V, a record for CH(NH2)2PbBr3 based devices. The outstanding photovoltage was obtained after improving the quality of the absorber layer and by optimizing the charge extraction layers. The causation of high photovolatge was investigated using a combination of techniques, such as field emission scanning electron microscopy, photothermal deflection absorption spectroscopy, impedance spectroscopy, time-integrated and time-resolved photoluminescence. In addition to insights gained through various structural, morphological and spectroscopic characterization techniques, the operational stability of the devices examined under aggressive conditions will also be discussed.

References:
1. Arora et al. submitted 2018.
2. Arora et al. Adv. Funct. Mater. 2016, 26, 2846-2854.
3. Arora et al. Nano Letters 2016, 16, 7155-7162.
4. Dar, M. I. et al. Chem Phy Lett. 2017, 683, 211-215.

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