Enhancing Photovoltaic Performance and Stability of All-inorganic and Lead-free Absorbers
Tsutomu Miyasaka a
a Toin University of Yokohama, 1614 Kurogane-cho, Aoba, Yokohama, 2258503, Japan
nanoGe Perovskite Conferences
Proceedings of nanoGe International Conference on Perovskite Solar Cells, Photonics and Optoelectronics (NIPHO19)
International Conference on Perovskite Thin Film Photovoltaics
Jerusalem, Israel, 2019 February 24th - 27th
Organizers: Lioz Etgar and Kai Zhu
Invited Speaker, Tsutomu Miyasaka, presentation 038
DOI: https://doi.org/10.29363/nanoge.nipho.2019.038
Publication date: 21st November 2018

Power conversion efficiency (PCE) of lead halide perovskite solar cell (over 23%) has surpassed those of CIGS and CdTe, approaching the top value of crystalline Si cell. However, high PCE of single-cell enabled by lead halide-based perovskite absorbers is now being saturated, taking the Shockley Queisser (SQ) limit of open-circuit voltage (VOC) (ca.1.32V) into account. A next challenge is to create a single cell which has high PCE comparable with that of GaAs (>28%) by reducing bandgap energy to <1.4 eV without accompaniment of increase in VOC loss. This possibility will be found in a family of metal halide perovskites or other hybrid materials without depending on use of lead because lead-based semiconductors will limit bandgap energy higher than 1.5 eV. Concerning efficiency enhancement, high performance of organo lead halide materials is not compatible with robust high stability required for practical use. Ensuring the intrinsic thermal stability (desirably >200oC) of the perovskites is a key issue before industrialization. In addition, toxicity of lead-based perovskites are going to become the most formidable challenges for real use (commercialization), in particular, for applications to IoT society, which is one of the most promising field of perovskite photovoltaic device in terms of high voltage output even under weak illumination. These thoughts urge us to concentrate our next research of perovskite photovoltaics (PV) more on development of non-lead high efficiency absorbers. Sn perovskite is still a strong candidate because Sn(II) has been found to be stabilized against ambient air by metal doping method (such as Ge). Regarding Bi-based perovskites, we found AgBi2I7 as a promising all-inorganic absorber having high thermal and moisture stability. Stability also highly depends on the property of charge transport materials (CTMs), especially, the kind of hole transporter. Spiro-OMeTAD does not work at high temperature while P3HT, for example, is thermally stable. In our collaboration with JAXA, P3HT-based perovskite devices showed robust stability by exposure to high (100oC) and low (-80oC) temperatures and also to high energy particle radiations (iScience, 2018, 2, 148). Selection of CTMs is another important key in combination with non-lead perovskite materials. In conclusion, next direction of perovskite PV should be to enhance PV performance of non-lead and all-inorganic semiconductor materials by extended compositional engineering, in parallel with developing thermally stable CTMs. Our on-going studies on all-inorganic perovskite absorbers and new CTMs for photovoltaic applications will be introduced in my talk.

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