Fully scalable HTM-free hybrid perovskite solar cells with carbon electrode

Sonya Kosar, Longbin Qiu, Yan Jiang, Luis K. Ono and Yabing Qi ** Energy Materials and Surface Sciences Unit, Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1 Tancha, Onna-son, Kunigami-gun,... [ view full abstract ]

Sonya Kosar, Longbin Qiu, Yan Jiang, Luis K. Ono and Yabing Qi ^*

^* Energy Materials and Surface Sciences Unit, Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1 Tancha, Onna-son, Kunigami-gun, Okinawa 904-0495, Japan

Email: Yabing.Qi@OIST.jp

   The organic-inorganic perovskite solar cells showed tremendous increase in efficiency during the recent decade, starting from 3.8%¹ and already saturating at 22%². The matter of further work is to make the device stable, scalable and inexpensive. Thus, much effort is being put into development of commercially more attractive perovskite solar cells without expensive hole transporting material with carbon top electrode instead of Au one. Additionally, despite common belief the applicability of solvent-assisted methods for the large-scale manufacturing of hybrid perovskite modules is still under debate. Thus, in this work, we demonstrate a combination of vacuum techniques for device preparation with inexpensive carbon counter electrode as a concept towards large scale fabrication of inexpensive perovskite solar cells.

   We offer to use hybrid chemical vapor deposition (HCVD) method³ to prepare high quality perovskite films and carbon paste as efficient hole-collecting electrode (the device structure is presented on Fig. 1a). The HCVD method allows successful diffusion of CH₃NH₃I vapor into thermally evaporated PbI₂ layer forming homogeneous CH₃NH₃PbI₃ film with large grains and smooth grain boundaries (Fig. 1b), which is beneficial for charge transfer.  

   Our best device shows efficiency of ~5% with V_oc of 0.93 V, J_sc of 12.4 mA/cm² and fill factor of 0.42 (Fig. 1c).  We believe that modification of carbon paste properties, e.g. increase of work function, is the key step towards further enhancing of power conversion efficiency. 

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