SnO₂‐C₆₀ Pyrrolidine Tris‐Acid (CPTA) as the Electron Transport Layer for Highly Efficient and Stable Planar Sn‐Based Perovskite Solar Cells

Abstract

For solar cell applications, Sn-based hybrid perovskites have drawn particular interest due to their environmental friendliness. Here, a thin layer of C 60 pyrrolidine tris-acid (CPTA) is found essential for achieving high efficiency with planar solar cells of Sn-based perovskites. As a result, a power conversion efficiency of 7.40% is achieved for {en}FASnI 3 solar cells with a planar n-i-p architecture, and the device exhibits excellent stability in air. For the first time, highly efficient Sn-based hybrid perovskite solar cells on n-i-p architecture are achieved. A V oc of 0.72 V is highlighted as the highest V oc ever reported for FASnI 3 solar cells.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201903621. and sometimes even short-circuit the devices. Several strategies have been developed to protect the Sn-based perovskite, such as the adding of SnF 2 , [10] controlling the reducing atmosphere, [11] the forming of 2D/3D composite [12,13] or 3D hollow structures. [14][15][16][17] In order to achieve higher efficiency and stability, Sn-based perovskite have relied on mesoporous TiO 2 as the electron-selective layer. [18,19] The introduction of mesoporous TiO 2 makes manufacture process more complex, and the high-temperature needed for processing hampers the development of perovskitebased monolithic tandem devices and flexible wearable solar cells. [20,21] In contrast, the simplicity of the planar heterojunction indicates that a planar architecture is more technically feasible. [22] Besides, planar PSCs can be fabricated via solution processing at low temperatures (<150 °C), thus greatly reducing manufacturing costs. However, compared to the mesoporoustype PSC, its planar-type counterpart suffers from very low PCE, [23,24] probably due to the poor contact of the interfaces [25] and unsuitable charge transporting layer. [23] Here, we tried SnO 2 as the electron transport layer to fabricate a n-i-p planar-architecture, but was not successful. Then we introduced a hydrophilic derivative of fullerene, namely, the C 60 pyrrolidine tris-acid (CPTA) between SnO 2 and the perovskite. As a result, we achieved a power conversion efficiency above 7.40% for Sn-based perovskite devices with the planar architecture. This shows that not only mesoporous-architecture devices, but also n-i-p planar-architecture devices can be highly efficient in the Sn-based PSCs. Thanks to the CPTA layer in our planar Sn-based PSCs, we attained a V oc of 0.72 V, which represents the highest value ever reported for FASnI 3 solar cells. Results and DiscussionWe fabricated Sn-based PSCs with the planar n-i-p architecture (Figure 1a). A SnO 2 compact layer deposited on the fluorine-doped tin oxide (FTO) substrate was employed as an electron transport layer. C 60 pyrrolidine tris-acid (CPTA) was then deposited onto the SnO 2 -covered FTO substrate. Figure 1b shows the X-ray diffraction (XRD) pattern of the {en}FASnI 3 films. The peaks of FTO substrate are marked with black dots. ...

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