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C8.02 - Infrared-Light-Responsible Perovskite Solar Cells Consisting of Sn and Pb 
April 9, 2015   2:00pm - 2:30pm

The certified efficiency of perovskite solar cells is now 17.9% and is reaching that of inorganic solar cells such as 20.4% of poly Si solar cells. According to our simulation, 20.4 % efficiency is obtained (IPCE:0.8 and FF:0.7) by using photo-absorber with 900nm absorption spectrum edge, when 0.3 V was taken as the voltage loss from the ideal voltage. We focused on infrared-photoconversion, because the infrared-responsible solar cells should be useful for the bottom cells of the tandem cells and for enhancing the efficiency of single cells by harvesting light up to 900 nm after the band gap tuning. It is well-known that CH3NH3SnI3 Perov Sn) has absorption in the area of infrared. However, it was difficult to handle the Perov Sn in open air condition. We found that the mixture of Sn perovskite and Pb perovskite (CH3NH3Sn(0.5)Pb(0.5)I3, Perov Pb/Sn) has improved stability under air with maintaining the photoconversion in the infrared area. The IPCE of the 950nm was 0.2. However, it was found that the absolute photoconversion efficiency (IQE: Internal quantum efficiency) was 0.75 (75%). The low IPCE in the infrared area was explained by the loss of light uptake. Therefore, it was concluded that the photon confinement in the layer of Perov Pb/Sn is needed for enhancing the conversion. The charge recombination between electrons in porous titania and P3HT for Perov Pb and that in Perov Pb/Sn(1:1) was 600?sec and 30?sec respectively. In order to retard the charge recombination, porous titania was passivated by wide gap oxide thin layers such as Al2O3, ZrO2 and Y2O3. Among then, Y2O3 passivation gave the best results. Urbach tail measured by Photo Acoustic Spectroscopy was compared between Perov Pb/Sn and Perov Pb and it was found that the Urbach tail for the Perov Pb/Sn was lower than that of Perov Pb. The tail and band gaps of Perov Pb/Sn varied, depending on the substrates from which Perov Pb/Sn crystals grow, suggesting that Perov Pb/Sn has gradient structures affected by the surface of the substrates and Sn:Pb ratio changed from the bottom layer to the top layer. The relationship between the structure of Perov Sn/Pb and the substrate surface is reported in detail.

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