(Invited) Recent Progresses in Solution-Processed Hybrid Perovskite Devices in Photovoltaics and Optoelectronics
Authors: Miyasaka Tsutomu 
Published: February 2020

Organo-lead trihalide perovskite compounds, represented by CH3NH3PbI3, exhibit many rare functions as narrow bandgap semiconductors (Fig. 1). In 2006, we have first employed CH3NH3PbBr3 and CH3NH3PbI3 as the sensitizer of electrochemical solar cell. 1a In 2008 this method was applied to make a first solid-state perovskite solar cell with carbon-polymer composite as a hole transport materialin.1c Recent rapid progress of perovskite-based photovoltaics (PV) has enabled power conversion efficiency (PCE) to reach 2２% (Fig. 2) . Our group has studied simple solution process for perovskite absorber preparation in ambient air conditions and achieved efficiency beyond 17%.2 Here, photocurrent-voltage (J-V) behavior of the perovskite PV cell was investigated to clarify the origin(s) of its hysteretic performance by focusing on the influence of interfacial structures.3

Perovskite cells can be fabricated by low temperature processes. Lightweight flexible photovoltaic cells will see enormous applications in power devices. We developed plastic film perovskite cells (PCE >13%), fabricated on ITO-PEN film by using brookite TiO2 as mesoporous layer, to demonstrate its high mechanical durability against repeated bending. As metal oxide electron collectors, ZnO/SnO2 composite films prepared at temperatures <120oC enabled PCE of perovskite cell exceeding 15%.4 Use of SnO2 collector is a new trend in perovskite PV in terms of high voltage and improvement of cell lifetime. The heat stability of perovskite device is an important issue for industrial applications. It is improved by using formamidinium (HC(NH2)2) that replaces CH3NH3. We made HC(NH2)2PbI3-based solar cells on low-temperature mesoporous ZnO. They exhibit relatively high stability for long time preservation with PCE as high as 16% (Fig. 3 left). HC(NH2)2PbI3 solar cell prepared on thin TiO2 layer exhibits high open circuit voltage (Voc)>1.1V with PEC >17% (Fig. 3 right).
Enormous potential of perovskite-based device is not only expected for power devices but also for high performance optical sensing devices. Organic lead trihalide perovskite can work as a high function semiconductor photodiode. We found that the gain of CH3NH3PbI3-induced diode photocurrent can reach a high level of the order of 103, showing excellent light-switching and current amplifying performance (Fig. 4)5. Such rare functions of the perovskite devices provide a lot of rooms to explore their versatile applications in photovoltaics and optoelectronics.
REFERENCES
1. a) A. Kojima, et al. Abstract #397, 210th ECS Meeting, 2006. b) ibid, Abstract #352, 212th ECS Meeting, 2007. c). ibid, PRiME 2008, Abstract #27, Honolulu,2008.
2. T. Miyasaka, Chem. Lett., 44, 720 (2015).
3. A. K. Jena, A. Kulkarni, M. Ikegami, T. Miyasaka, J
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4. J. Song, E. Zheng, X.-F. Wang, W. Tian, T. Miyasaka, Solar Ener
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5. H.-W. Chen, N. Sakai, A. K. Jena, Y. Sanehira, M. Ikegami, K.-C. Ho, T. Miyasaka, J. Phys. Chem. Lett., 6, 1773(2015)

Figure 1