Electron transport enhancement in perovskite solar cell via the polarized BaTiO 3 thin film
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The ferroelectric material of BaTiO3 was introduced in the electron transport layer (ETL) of perovskite solar cells to improve the photogenerated electron transport. The sintered BaTiO3 thin films were polarized at different applied electric fields, and then TiO2 thin films were further deposited to be used as the ETL. The electric field was positively applied across the BaTiO3 thin film, and the photocurrent density of solar cell can be increased obviously. The results of electrochemical impedance and photoluminescence spectra indicate that the ordered polarization dipole moment inside the BaTiO3 thin film can accelerate the transport of photogenerated electrons from the ETL to the conducting glass substrate. The short-circuit photocurrent of perovskite solar cell is increased and thus the light-to-electric conversion efficiency is effectively improved to 13%. It is increased by 14% compared with that without the application of the positive electric field across the BaTiO3 thin film.
INTRODUCTION Perovskite solar cells have attracted widespread attention in the field of photovoltaic devices since 2009 [1]. In the past ten years, perovskite solar cells have been developed rapidly due to its advantages of low manufacturing cost, high light absorption coefficient, high mobility, adjustable band gap and long carrier life. The perovskite itself has large dielectric constant and small exciton binding energy and dissociates into free-moving electron–hole carriers at room temperature. The transport of free carriers in the perovskite layer is fast enough [2,3]. Up to now, the recorded photoelectric conversion efficiency of perovskite/silicon tandem solar cell was updated to 25.2% [4]. Hence, perovskite solar cell has become one of the most promising solar cells. In the future research of perovskite solar cells, it is more focused on how to improve light-to-electric conversion efficiency and stability of the cells. Usually, perovskite solar cell is mainly composed of electron transport layer (ETL), perovskite light-absorbing layer and hole transport layer [5,6,7]. Organic–inorganic hybrid perovskites are widely used as light-absorbing materials, for example, CH3NH3PbX3 (X = I, Br, Cl). Due to the high
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mobility of free carriers in the perovskite layer, the transport of photogenerated electrons in the ETL is relatively slower. To further improve light-to-electric conversion efficiency of perovskite solar cells, it is an important way to improve the electron transport process in the ETL. Mesoporous TiO2 thin film is widely used as the ETL in perovskite solar cells [8]. As an electron transport material, TiO2 not only satisfies the energy level matching with other layers but also effectively extracts electrons generated by the perovskite light-absorbing layer and blocks holes [9,10]. In addition, mesoporous TiO2 thin film with a large specific surface area can allow deposition of more perovskite materials, which can effectively capture more electrons in the ETL [11]. Even though TiO2 is diff
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