Synergistic Effect of Fluorinated Passivator and Hole Transport Dopant Enables Stable Perovskite Solar Cells with an Efficiency Near 24%

Abstract

Long-term durability is critically important for the commercialization of perovskite solar cells (PSCs). The ionic character of the perovskite and the hydrophilicity of commonly used additives for the hole-transporting layer (HTL), such as lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and tertbutylpyridine (tBP), render PSCs prone to moisture attack, compromising their long-term stability. Here we introduce a trifluoromethylation strategy to overcome this drawback and to boost the PSC's solar to electric power conversion efficiency (PCE). We employ 4-(trifluoromethyl)benzylammonium iodide (TFMBAI) as an amphiphilic modifier for interfacial defect mitigation and 4-(trifluoromethyl)pyridine (TFP) as an additive to enhance the HTL's hydrophobicity. Surface treatment of the triple-cation perovskite with TFMBAI largely suppressed the nonradiative charge carrier recombination, boosting the PCE from 20.9% to 23.9% and suppressing hysteresis, while adding TFP to the HTL enhanced the PCS's resistance to moisture while maintaining its high PCE. Taking advantage of the synergistic effects resulting from the combination of both fluoromethylated modifiers, we realize TFMBAI/TFP-based highly efficient PSCs with excellent operational stability and resistance to moisture, retaining over 96% of their initial efficiency after 500 h maximum power point tracking (MPPT) under simulated 1 sun irradiation and 97% of their initial efficiency after 1100 h of exposure under ambient conditions to a relative humidity of 60−70%.

Two birds with one stone: dual grain-boundary and interface passivation enables >22% efficient inverted methylammonium-free perovskite solar cells

“…Single-junction organic-inorganic metal halide perovskite solar cells (PSCs) have demonstrated outstanding performance in laboratory-scale devices, closing the gap to the highest reported power conversion efficiencies (PCEs) of the market-dominating Si solar cells. 1,2 While PCEs above 23% have been demonstrated using the mesoporous [3][4][5][6][7][8][9][10][11][12] and planar [13][14][15][16][17][18][19][20][21][22] n-i-p architecture (up to 25.5% certified 23 ), inverted planar p-i-n PSCs still lag behind despite several recent studies reporting PCEs above 22% (up to 22.75% certified 24 ) (see Fig. S1).…”

Cyclopentadiene‐Based Hole‐Transport Material for Cost‐Reduced Stabilized Perovskite Solar Cells with Power Conversion Efficiencies Over 23%

“…[ 30 ] This higher IE value should be advantageous for the energy level alignment within the solar cell, assuming an IE value of 5.46 eV for the perovskite layer. [ 31 ] As shown by Polander et al., a smaller difference in IE between perovskite and HTM results in higher values of V OC , as long as no extraction barrier is introduced, meaning that the HTM's IE should not be larger than the one of the perovskite. [ 32 ] A corresponding energy level diagram for the PSCs including the HTMs CPDA 1 and spiro‐OMeTAD is shown in Figure S10, Supporting Information.…”

The Non‐Innocent Role of Hole‐Transporting Materials in Perovskite Solar Cells

“…Other remarkable crosslinking approaches reported in the past two years by different groups regard the incorporation of fluorine moieties within a crosslinkable and dopant-free smallmolecule HTM to further boost hydrophobicity of the chargeextracting layer and target defect-passivating interactions with the perovskite surface, [135] the use of electropolymerization to induce in situ formation of polyamine-based dopant-free HTMs for inverted PSCs, [136] and the in situ thermal conversion of solution-processable xanthate precursors into the corresponding insoluble glycol-derivatized poly(1,4-phenylenevinylene) HTMs with different hydrophilicity profiles influencing final device performance. [137] The insertion of an interfacial layer between the perovskite and the HTM or the HTM and the top metal electrode has been shown in other cases to be advantageous for reducing charge recombination in PSCs, [138,139] also through the passivation of surface defects in the semiconductor. [140][141][142] Engineering of the perovskite/HTM interface at the molecular level has even allowed Seo and coworkers to achieve outstanding PSC performance (a PCE of 22.7%) and stability, using a pristine, undoped P3HT HTM, [143] which normally provides relatively low PCEs (10-15%, [39,144] slightly better ones if doped [145,146] ).…”