Perovskite solar cells with wide band gap and narrow band gap
Shuzi Hayase a
a i-Powered Energy System Reserach Center, The University of Electro-Communications
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP20)
Tsukuba-shi, Japan, 2020 January 20th - 22nd
Organizers: Michio Kondo and Takurou Murakami
Keynote, Shuzi Hayase, presentation 009
DOI: https://doi.org/10.29363/nanoge.iperop.2020.009
Publication date: 14th October 2019

 

The efficiency of Pb-perovskite solar cells with more than 1 cm2 is 20.9 % which became close to those of inorganic multi-crystalline solar cells such as MC-Si, CIGS, and CdTe. In small cells with less than 1cm2, the efficiency of 25.2% has just been reported for the perovskite solar cells.

 

Conventional perovskite solar cells consisting of Pb have band gap of 1.5-1.6 eV and can harvest the light in the visible region up to 850nm.  According to Shockley-Queisser limit, light harvesting layer with 1.2-1.4 eV band gap gives the highest efficiency. Mixed metal PbSn perovskite materials have a narrow band gap of around 1.2 eV.  Therefore, mixed metal SnPb perovskite solar cell is expected to give higher efficiency than Pb-perovskite solar cells.  In addition, the narrow band gap solar cell is useful for bottom cells for all perovskite tandem solar cells. When SnPb mixed metal perovskite solar cells was firstly reported by us, the efficiency was around 4%. However, the efficiency has been enhanced gradually and recently efficiency higher than 20% has been reported by several groups including our Lab.  How the efficiency was enhanced will be discussed in the presentation1-4.

 

  The conventional perovskite layer consists of Pb ions. The use of Pb ions is limited by the law such as RoHS directive in Europe.  From this view point, there is a strong request for Pb-free perovskite solar cells solar cells. Bismuth halide compounds such as Cs3Bi2I9, MA3Bi2I9 Ag3BiI6, AgBi2I7, Cs2AgBiBr6, antimony halide compounds such as Rb3Sb2I9, titanium halide compounds such as Cs2TiBr6, and copper halide compounds such as MA2CuI4 have been reported to replace lead. However, the solar cell efficiency based on these materials were less than 5% and was not satisfactory.  Among all lead-free perovskite materials, Sn-based perovskite is one of the most promising candidates as the light harvesting layer for Pb-free PSCs, because they have perovskite structure similar to Pb perovskite.  In addition, the band gap is narrow (1.4eV). The efficiency has been enhanced to 10% by several research groups including us, however, the efficiency is not still satisfactory, when compared with Pb-perovskite. The cause of the low efficiency and how the efficiency will be enhanced is discussed5-7.

 

  Perovskite solar cells with wide gap of 1.7-1.8 eV are needed for making tandem cells consisting of SnPb perovskite solar cells as the bottom layer. CsPbI2Br is one of the candidates for the top perovskite layers. However, the efficiency was not satisfactory because of large Voc losses.  We will report CsPbI2Br solar cells with 1.34V (Voc) and 14% efficiency.  We discuss how Voc loss is decreased to enhance the efficiency8,9.

 

 

 

 

 

 

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