Evidence of Spiro-OMeTAD De-doping by tert-Butylpyridine Additive in Hole-Transporting Layers for Perovskite Solar Cells

Abstract

Spiro-OMeTAD is the most-employed molecular hole-transporting material (HTM) in n-i-p perovskite solar cells (PSCs). Ease of processing from solution and good filmability on top of the perovskite photo-active layer are characteristics that make this HTM outstanding and incomparable for the role. However, chemical doping with both tert-butylpyridine (tBP) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), coupled with further oxidation steps, is required in order to achieve high hole mobility and conductivity. Previous investigations have revealed that tBP is fundamental for addressing the best morphology in the hole-transporting layer during processing. Here, we provide spectroscopic evidence of the detrimental impact on long-term conservation of Spiro-OMeTAD structural and electrical properties when tBP is used as an additive. These aspects are crucial for the future design and understanding of new molecular HTMs for PSCs.

Capturing Mobile Lithium Ions in a Molecular Hole Transporter Enhances the Thermal Stability of Perovskite Solar Cells

“…[8] Furthermore, the de-doping of tBP within the hole-transport layer induces irreversible reorganization of the MHT. [9,10] Different types of organic and inorganic nanomaterials have been attempted for improving the thermal stability of PSCs. For instance, the integration of 2D transition metal dichalcogenides in PSCs has shown significant improvement in both environmental and thermal stabilities of the devices.…”

Ambient Fabrication of Organic–Inorganic Hybrid Perovskite Solar Cells

“…Such additives are essential to obtain high hole mobility and conductivity. [ 256 ] Since Li‐TFSi is hydroscopic, additive solutions as well as both Spiro‐OMeTAD and PTAA are typically prepared in a glovebox to reduce risk of moisture reaching the underlying perovskite layer. Cobalt complexes, such as Tris[2‐((1 H ‐pyrazol‐1‐yl)‐4‐ tert ‐butylpyridine) cobalt(III) tris(bis(trifluoromethylsulfonyl)imide)] (FK209), a less hygroscopic dopant, have also been used as an additive in Spiro‐OMeTAD.…”

Conformal monolayer contacts with lossless interfaces for perovskite single junction and monolithic tandem solar cells

“…14 Although highest reported power conversion efficiencies (PCEs) of over 23% are demonstrated for PSCs with the ''regular'' n-i-p device architecture, 15 the p-i-n (so called ''inverted'') architecture is gaining increasing popularity due to its ease of processing and superior suitability for perovskitebased tandem solar cells. [16][17][18][19] Moreover, p-i-n PSCs carry the promise of low-temperature fabrication, high stability 20 without the use of dopants that cause degradation, [21][22][23] low currentvoltage hysteresis 24 and compatibility to flexible substrates. 25,26 However, compared to their n-i-p single junction counterparts, p-i-n PSCs still lack behind in maximum power-conversion efficiency.…”