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Shengzhong (Frank) Liu1 2

1, Chinese Academy of Sciences, Dalian, , China
2, Shaanxi Normal University, Xi'an, , China

A new type perovskite, a hybrid material with both organic and inorganic components, has appeared to be a wonder for its excellent optical absorption, long range charge-carrier diffusion and apparent tolerance to defects. In the last few years, it has been emerged as a primary candidate material for various photovoltaic, optoelectronic and photoelectronic applications. In just a few years, the power conversion efficiency (PCE) of the perovskite solar cells has been improved from 3.8% to >22%. Moreover, the solar cell fabrication processes based on the planar architecture have been particularly enthusiastic thanks to their low temperature fabrication and compatibility with a range of substrates. Comparing solution deposition and vacuum deposition, the vacuum processes for thermal co-deposition and sequential deposition of PbCl2 and CH3NH3I materials are recognized as efficient means to prepare perovskite film with good uniformity and high surface coverage.
A vacuum deposition process has been developed to fabricate high efficiency perovskite solar cells with high stability using alternating layer-by-layer vacuum deposition. The new deposition process allows us to relax the strict deposition monitoring and control measures, while realizing superior uniformity in film morphology, surface coverage and smoothness, together with crystalline phase purity. The power conversion efficiencies for the planar device is as high as 19.6% on rigid glass substrate, the highest reported at the time. More importantly, we have developed a superior low temperature TiO2 coating and transferred the cell fabrication process onto lightweight flexible polymeric substrate. The highest cell efficiency achieved was over 16%, it is also the highest efficiency among the flexible perovskite cells reported. Our current status for the rigid thin film cell efficiency is over 21.5% and that for the flexible device over 18.3%, both are the highest for their respective category. Meanwhile, the devices show very good stability over long term exposure in ambient with very low degradation. After a representative cell was exposed in ambient lab condition for a year, its final cell efficiency is as high as over 95% of its initial efficiency with its degradation accounts for only smaller than 5%. Further analysis on the stability of the perovskite solar cells will be discussed.
We have also developed a series of single-crystalline perovskites with superior stability and optoelectronic performance.
References
[1] D. Yang, R. Yang, X. Ren, X. Zhu, Z. Yang, C. Li, S. Liu*, Advanced Materials, http://dx.doi.org/10.1002/adma.201600446.
[2] D. Yang, R. Yang, J. Zhang, Z. Yang, S. Liu, C. Li, Energy Environ. Sci. 2015, 8, 3208.
[3] D. Yang, Z. Yang, W. Qin, Y. Zhang, S. Liu, C. Li, J. Mater. Chem. A 2015, 3, 9401.

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