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      Amino-functionalized conjugated polymer electron transport layers enhance the UV-photostability of planar heterojunction perovskite solar cells†

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          Abstract

          Long-term photostability and high performance were achieved by perovskite solar cells with an amino-functionalized conjugated polymer as a new electron transport layer.

          Abstract

          In this study, for the first time, we report a solution-processed amino-functionalized copolymer semiconductor (PFN-2TNDI) with a conjugated backbone composed of fluorine, naphthalene diimide, and thiophene spacers as the electron transporting layer (ETL) in n–i–p planar structured perovskite solar cells. Using this copolymer semiconductor in conjunction with a planar n–i–p heterojunction, we achieved an unprecedented efficiency of ∼16% under standard illumination test conditions. More importantly, the perovskite devices using this polymer ETL have shown good stability under constant ultra violet (UV) light soaking during 3000 h of accelerated tests. Various advanced spectroscopic characterizations, including ultra-fast spectroscopy, ultra-violet photoelectron spectroscopy and electronic impedance spectroscopy, elucidate that the interaction between the functional polymer ETL and the perovskite layer plays a critical role in trap passivation and thus, the device UV-photostability. We expect that these results will boost the development of low temperature solution-processed organic ETL materials, which is essential for the commercialization of high-performance and stable, flexible perovskite solar cells.

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          Most cited references 37

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          Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3NH3PbI3 planar heterojunction solar cells.

          The large photocurrent hysteresis observed in many organometal trihalide perovskite solar cells has become a major hindrance impairing the ultimate performance and stability of these devices, while its origin was unknown. Here we demonstrate the trap states on the surface and grain boundaries of the perovskite materials to be the origin of photocurrent hysteresis and that the fullerene layers deposited on perovskites can effectively passivate these charge trap states and eliminate the notorious photocurrent hysteresis. Fullerenes deposited on the top of the perovskites reduce the trap density by two orders of magnitude and double the power conversion efficiency of CH(3)NH(3)PbI(3) solar cells. The elucidation of the origin of photocurrent hysteresis and its elimination by trap passivation in perovskite solar cells provides important directions for future enhancements to device efficiency.
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            Growth of CH3NH3PbI3 cuboids with controlled size for high-efficiency perovskite solar cells.

            Perovskite solar cells with submicrometre-thick CH(3)NH(3)PbI(3) or CH(3)NH(3)PbI(3-x)Cl(x) active layers show a power conversion efficiency as high as 15%. However, compared to the best-performing device, the average efficiency was as low as 12%, with a large standard deviation (s.d.). Here, we report perovskite solar cells with an average efficiency exceeding 16% and best efficiency of 17%. This was enabled by the growth of CH(3)NH(3)PbI(3) cuboids with a controlled size via a two-step spin-coating procedure. Spin-coating of a solution of CH(3)NH(3)I with different concentrations follows the spin-coating of PbI(2), and the cuboid size of CH(3)NH(3)PbI(3) is found to strongly depend on the concentration of CH(3)NH(3)I. Light-harvesting efficiency and charge-carrier extraction are significantly affected by the cuboid size. Under simulated one-sun illumination, average efficiencies of 16.4% (s.d. ± 0.35), 16.3% (s.d. ± 0.44) and 13.5% (s.d. ± 0.34) are obtained from solutions of CH(3)NH(3)I with concentrations of 0.038 M, 0.050 M and 0.063 M, respectively. By controlling the size of the cuboids of CH(3)NH(3)PbI(3) during their growth, we achieved the best efficiency of 17.01% with a photocurrent density of 21.64 mA cm(-2), open-circuit photovoltage of 1.056 V and fill factor of 0.741.
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              Overcoming ultraviolet light instability of sensitized TiO₂ with meso-superstructured organometal tri-halide perovskite solar cells.

              The power conversion efficiency of hybrid solid-state solar cells has more than doubled from 7 to 15% over the past year. This is largely as a result of the incorporation of organometallic trihalide perovskite absorbers into these devices. But, as promising as this development is, long-term operational stability is just as important as initial conversion efficiency when it comes to the development of practical solid-state solar cells. Here we identify a critical instability in mesoporous TiO₂-sensitized solar cells arising from light-induced desorption of surface-adsorbed oxygen. We show that this instability does not arise in mesoporous TiO₂-free mesosuperstructured solar cells. Moreover, our TiO₂-free cells deliver stable photocurrent for over 1,000 h continuous exposure and operation under full spectrum simulated sunlight.
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                Author and article information

                Journal
                Chem Sci
                Chem Sci
                Chemical Science
                Royal Society of Chemistry
                2041-6520
                2041-6539
                1 June 2017
                19 April 2017
                : 8
                : 6
                : 4587-4594
                Affiliations
                [a ] Wuhan National Laboratory for Optoelectronics , Huazhong University of Science and Technology , Wuhan , Hubei 430074 , China . Email: mingkui.wang@ 123456mail.hust.edu.cn
                [b ] Institute of Polymer Optoelectronic Materials and Devices , State Key Laboratory of Luminescent Materials and Devices , South China University of Technology , Guangzhou , Guangdong 510640 , China . Email: msangusyip@ 123456scut.edu.cn ; Email: msfhuang@ 123456scut.edu.cn
                [c ] Wuhan National High Magnetic Field Center , Huazhong University of Science and Technology , 1037 Luoyu Road , Wuhan 430074 , Hubei , China
                Article
                c7sc00077d
                10.1039/c7sc00077d
                5618109
                This journal is © The Royal Society of Chemistry 2017

                This is an Open Access article distributed under the terms of the Creative Commons Attribution 3.0 Unported License ( http://creativecommons.org/licenses/by/3.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Chemistry

                Notes

                †Electronic supplementary information (ESI) available: Experimental details, AFM, UPS. See DOI: 10.1039/c7sc00077d

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