Material Engineering toward High Performance Perovskite Solar Cells
Hiroshi Segawa a b
a Graduate School of Arts and Sciences, The University of Tokyo, Komaba 3-8-1, Tokyo 153-8902, Japan.
b Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo 153-8904, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference on Perovskite and Organic Photovoltaics and Optoelectronics (IPEROP19)
Kyōto-shi, Japan, 2019 January 27th - 29th
Organizers: Hideo Ohkita, Atsushi Wakamiya and Mohammad Nazeeruddin
Invited Speaker, Hiroshi Segawa, presentation 018
Publication date: 23rd October 2018

Organometal halide perovskites have captured wide interest as a promising material for low-cost and high-efficiency solar cells [1, 2].

Through recent studies of organometal halide perovskite solar cells (PSCs), the composition of organometal halide perovskites is recognised as one of the key factors in the improvement of the PCE. In this study, we investigated cation-doping into the perovskite absorber. [3, 4, 5] The results revealed that incorporating a small amount of K+ into the double organic cation perovskite absorber (FA0.85MA0.15Pb(I0.85Br0.15)3) improved the photovoltaic performance of PSCs significantly, and K+ incorporation diminished I-V hysteresis. Consequently, the PSCs of more than 20% power conversion efficiency (PCE) without I-V hysteresis were constructed. The crystal lattice of the organometal halide perovskite was expanded with increasing of the potassium ratio, where both absorption and photoluminescence spectra shifted to the longer wavelength, suggesting that the optical band gap decreased. It is concluded that stagnation-less carrier transportation could minimise the I-V hysteresis of PSCs.

On the other hand, the microstructural aspects within the organometal halide perovskite are still unknown, even though it belongs to a crystal system. In this study, direct observation of the microstructure of the thin film organometal halide perovskite using transmission electron microscopy was investigated [6]. Unlike previous reports, it is identified that the tetragonal and cubic phases coexist at room temperature, and it is confirmed that superlattices composed of a mixture of tetragonal and cubic phases are selforganized without a compositional change. The organometal halide perovskite self-adjusts the configuration of phases and automatically organizes a buffer layer at boundaries by introducing a superlattice. These results shows the fundamental crystallographic information for the organometal halide perovskite and demonstrates new possibilities toward high performance perovskite solar cells.

The author thanks for financial supports from New Energy andIndustrial Technology Development Organization (NEDO, Japan)through their project “Development of high performance and reli-able PV modules to reduce levelized cost of energy/Research anddevelopment of innovative new structure solar cells/Developmentof innovative low production cost solar cells based on perovskite-type materials”.

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