A Multifaceted Ferrocene Interlayer for Highly Stable and Efficient Lithium Doped Spiro‐OMeTAD‐based Perovskite Solar Cells

Abstract

hole mobilities within the HTL of up to 1.6 × 10 -3 cm 2 V -1 s -1 . [4] However, the use of such highly hygroscopic lithium salts has been shown to dramatically accelerate the degradation of PSCs. [5][6][7][8] Previous works have identified that upon doping with LiTFSI, lithium ions can readily become mobile and diffuse within the perovskite layer, forming hygroscopic LiX salts (where Xis a halide) which in turn rapidly degrade the perovskite. [5,[9][10][11][12][13][14] Wang et al demonstrated that following evaporation of tert-butylpyridine (tBP), a common spiro-OMeTAD additive, LiTFSI begins to form hygroscopic aggregates which hydrate the perovskite/spiro-OMeTAD interface degrading the perovskite over a period of < 1000 hours. [8] Furthermore, it has also been shown that tBP is, by itself, insufficient to prevent the migration of lithium ions. [7] To this extent, Kim et al. recently revealed that the migration of Li + is critical in the degradation of spiro-OMeTAD-based devices and is accelerated at higher temperatures, leading to the rapid degradation of the perovskite. [7] For these combined reasons spiro-OMeTAD-based PSCs consistently fall short of the practical requirements for the commercialization of solar cells. Indeed, the poor stability of LiTFSI doped spiro-OMeTAD as an HTL has become such a problem that many leading studies using the architecture replace the HTL with a more stable, yet lower efficiency, alternative or emit reporting stability entirely. [6,15] Consequently, addressing the impact of lithium on device stability is one of the biggest challenges facing the highest efficiency PSCs.As of writing, two principal strategies have emerged within the literature for improving the stability of n-i-p PSCs, namely (i) searching for new less destructive dopants or (ii) replacing spiro-OMeTAD in favor of alternative stable HTLs such as poly(triarylamine) (PTAA), poly(3-hexathiophene) (P3HT) or a range of novel molecular transporting materials (Table S1, Supporting Information). [5,[16][17][18] While these candidates can yield improvements in the long-term stability, the PCEs of resultant devices remain inferior to the spiro-OMeTAD counterparts. This performance gap has led to a trade-off between efficiency and stability in PSCs. More recently the formation of a blocking layer between the lithium doped spiro-OMeTAD HTL and the perovskite has been suggested using either graphene or flower-like MoS 2 . [11,19] Similar to the previous approaches, devices prepared using a blocking layer have yet to match the high efficiencies achieved using the conventional spiro-OMeTAD architecture, reaching up to 20.18% in devices prepared with MoS 2 . Furthermore, by blocking the Li + at the interface, the mechanism by which hygroscopic agregates are formed is not avoided. This challenge, therefore, requires new strategies that target the Li + ions within the HTL itself, preventing the accumulation of Li + at the interface and subsequent degradation. Very recently, several studies have sought to replace the Li + metal ...

Moisture‐Accelerated Precursor Crystallisation in Ambient Air for High‐Performance Perovskite Solar Cells toward Mass Production

“…To investigate thermal stability, the PSCs were aged under ISOS-T-1 conditions. [40,41] The PSPP device retained 84 % of the initial PCE after the aging test of heating at 60 °C with 40 % RH for 1224 h, compared with 59 % for the control PSC (Figure 5b). Notably, the PSCs in the aforementioned aging test employed LiTFSI and 4-tert-butylpyridine co-doped spiro-OMeTAD as the hole transport layer.…”

Halide Chemistry in Tin Perovskite Optoelectronics: Bottlenecks and Opportunities

“…[80] We also exploited ferrocene as a perovskite surface potential modifier at (FAPbI 3 ) 0.95 (MAPbBr 3 ) 0.05 /spiro-OMeTAD (HTL) junctions. [81] This avenue yielded i) enhanced charge transfer from perovskite to spiro-OMeTAD (Figure 7d,e) and ii) highly efficient solar cells (23.45 %) with high operational stability (70 % performance retention after 1250 h). Similarly, we demonstrated that ultrathin polymethylmethacrylate (PMMA) interlayers can effectively enhance selectivity at PEDOT:PSS/(PEA) 0.2 (FA) 0.8 SnI 3 interfaces and boost solar cell performance from 6.5 % to 10 % (Figure 7f).…”

Inhibiting Li+migration by thenoyltrifluoroacetone toward efficient and stable perovskite solar cells

“…16 In addition to the structural design and modification aimed at the HTL itself and its dopant composition, selecting suitable Li + migration inhibitors to modify and regulate the interface between the perovskite and HTL layer is also a potential method to inhibit Li + migration. 17 Besides Li + migration, there exist potential barriers at the perovskite/spiro-OMeTAD interface, which lead to energy loss and the impeding of hole extraction. 18 Choosing suitable Li + migration inhibitors as interface modifiers can not only inhibit Li + migration, but can also take the stability and charge extraction properties of the perovskite/HTL interface into consideration, which is of great significance for further improving device stability.…”