New Generation Hole Transporting Materials for Perovskite Solar Cells: Amide‐Based Small‐Molecules with Nonconjugated Backbones

Abstract

with outstanding optoelectronic properties. [1] In 2009, these materials were introduced in solar cells and have since established a striking increase in performance, reaching over 22% in stateof-the-art devices. [2] Here, the perovskite absorber is sandwiched between two selective charge extraction layers, that transport the charges to the electrodes. [3] Although efficient inorganic hole transporting materials (HTMs) have been reported, [4] the most well-known HTMs are the organic materials 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′spirobifluorene (Spiro-OMeTAD) and polytriarylamine (PTAA). Alternatives that compete in performance have been published, [5][6][7] however, just like Spiro-OMeTAD and PTAA, most of these materials are synthesized in multistep synthetic procedures, involving (transition) metal catalyzed cross-coupling reactions, stringent reaction conditions and extensive product purification. This results in a relative high material cost, consequently leading to a significant contribution to the total device cost. [5,8,9] Additionally, the tedious synthesis hampers large State-of-the-art perovskite-based solar cells employ expensive, organic hole transporting materials (HTMs) such as Spiro-OMeTAD that, in turn, limits the commercialization of this promising technology. Herein an HTM (EDOT-Amide-TPA) is reported in which a functional amide-based backbone is introduced, which allows this material to be synthesized in a simple condensation reaction with an estimated cost of <$5 g −1 . When employed in perovskite solar cells, EDOT-Amide-TPA demonstrates stabilized power conversion efficiencies up to 20.0% and reproducibly outperforms Spiro-OMeTAD in direct comparisons. Time resolved microwave conductivity measurements indicate that the observed improvement originates from a faster hole injection rate from the perovskite to EDOT-Amide-TPA. Additionally, the devices exhibit an improved lifetime, which is assigned to the coordination of the amide bond to the Li-additive, offering a novel strategy to hamper the migration of additives. It is shown that, despite the lack of a conjugated backbone, the amide-based HTM can outperform state-of-the-art HTMs at a fraction of the cost, thereby providing a novel set of design strategies to develop new, low-cost HTMs.

Enamine‐Based Cross‐Linkable Hole‐Transporting Materials for Perovskite Solar Cells

“…Following a previously published procedure, [ 3 ] the costs of the materials used for the synthesis were evaluated (detailed calculations can be found in the Supporting Information). The calculated price of the materials is 13.56 and 16.34€ g −1 for V1162 and V1187, respectively, which is somewhat higher than the lowest reported costs of organic HTMs (e.g., V950 ≈6€ g −1 [ 11 ] and EDOT–amide–TPA ≈5$ g −1 [ 27 ] ); however, it is significantly lower than that of the most popular HTM Spiro‐OMeTAD (93$ g −1 [ 28 ] ).…”

Oxidative Passivation of Metal Halide Perovskites

“…This perovskite composition has also proved to be more stable in thin-film solar cells with reported device efficiencies that surpass 20%. 32,33 First, we use PL spectroscopy to investigate the effects of the H 2 O 2 post-treatments on the optoelectronic properties of the perovskite films. In Figures 1A and 1B, we show steady-state and time-resolved PL measurements of thin films of FA 0.83 Cs 0.17 Pb(I 0.83 Br 0.17 ) 3 treated via the wet method.…”

Efficiencyvs.stability: dopant-free hole transporting materials towards stabilized perovskite solar cells

“…The second one, Z30 based on phenothiazine, showed a slightly lower performance of 19.2% 134. Petrus et al introduced an amide-functionality in the backbone of HTMs to synthesize an EDOT-Amide-TPA material by a simple condensation reaction which showed a very high performance of 20.3% 135. Phenoxazine-based POZ10 reported by Chen and co-workers showed a PCE of 19.4% 136.…”