Passivation of interfacial defects serves as an effective means to realize highly efficient and stable perovskite solar cells (PSCs). However, most molecular modulators currently used to mitigate such defects form poorly conductive aggregates at the perovskite interface with the charge collection layer, impeding the extraction of photogenerated charge carriers. Here, a judiciously engineered passivator, 4‐tert‐butyl‐benzylammonium iodide (tBBAI), is introduced, whose bulky tert‐butyl groups prevent the unwanted aggregation by steric repulsion. It is found that simple surface treatment with tBBAI significantly accelerates the charge extraction from the perovskite into the spiro‐OMeTAD hole‐transporter, while retarding the nonradiative charge carrier recombination. This boosts the power conversion efficiency (PCE) of the PSC from ≈20% to 23.5% reducing the hysteresis to barely detectable levels. Importantly, the tBBAI treatment raises the fill factor from 0.75 to the very high value of 0.82, which concurs with a decrease in the ideality factor from 1.72 to 1.34, confirming the suppression of radiation‐less carrier recombination. The tert‐butyl group also provides a hydrophobic umbrella protecting the perovskite film from attack by ambient moisture. As a result, the PSCs show excellent operational stability retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking under continuous simulated solar irradiation.

We prepared the novel fullerene derivative (a-bis-PCBM) by separating it from the as-produced bis-phenyl-C 61 -butyric acid methyl (bis-[60] PCBM) ester isomer mixture using preparative peak-recycling high performance liquid chromatography (HPLC). We employed the compound as a templating agent for the solution processing of metal halide perovskite films by the antisolvent method. Perovskite solar cells (PSCs) containing a-bis-PCBM perovskite achieve better stability, efficiency, and reproducibility compared with those employing traditional PCBM. The a-bis-PCBM can fill the vacancies and grain boundaries of the perovskite film, enhancing the crystallization of perovskites and addressing the issue of 2 slow electron extraction. In addition, it can also resist the ingression of moisture, protect the interfaces from chemical erosion, and passivate the voids or pinholes generated in the holetransporting layer. As a result, we obtain an outstanding power conversion efficiency (PCE) of 20.8 % compared with 19.9 % by PCBM, accompanied by excellent stability under heat and simulated sunlight,. The PCE of unsealed devcies dropped by less than 10% in ambient air (40% RH) after 44 days at 65 ℃ and by 4% after 600 h under continuous full sun illumination and maximum power point tracking respectively.Hybrid organic-inorganic lead halide perovskite solar cells (PSCs) have emerged as a promising candidate for the next generation photovoltaic technology due to their low manufacturing cost and high performance. 1−6 Through judicious manipulation of perovskite morphology and improvement of interfacial properties, 2−6 PSCs have reached a certified power conversion efficiency (PCE) up to 22.1%. 7 Generally, the PSCs with the best performance employ a sandwich configuration, composed of a layer of TiO 2 electron selective contact, which is infiltrated by the intrinsic perovskite light harvester, followed by a layer of hole transport material (HTM) as p-type contact and a metal back contact. 8 Despite of these stunning advances, several challenges still remain before PSCs become a competitive commercial technology, one crucial issue being the device stability. 9−11 Uncontrolled film morphology associated with poor crystallity of the perovskites results in low efficiency and poor reproducibility of the device performance. 12 Previous studies have indicated that the degradation of PSCs is primarily governed by the ingress of atmospheric oxygen and water vapor into the film upon exposure to air, which in turn causes undesired reactions with the active materials. 13,14 Various methods have been tried to modify the morphology of perovskite films aiming to improve the stability, for example, poly(methyl methacrylate) (PMMA) was used as a template to control nucleation and crystal growth, resulting in considerable increase in both the device efficiency and stability when kept under 3 dry condition in the dark. 15 Other studies use additives like 1-methyl-3-(1H,1H,2H,2H-nonafluorohexyl)-imidazolium iodide, 16 or phenyl-C 61 -b...

Directing efficient hole transport Surface defects in three-dimensional perovskites can decrease performance but can be healed with coatings based on two-dimensional (2D) perovskite such as Ruddlesden-Popper phases. However, the bulky organic groups of these 2D phases can lead to low and anisotropic charge transport. F. Zhang et al . show that a metastable polymorph of a Dion-Jacobson 2D structure based on asymmetric organic molecules reduced the energy barrier for hole transport and their transport through the layer. When used as a top layer for a triple-cation mixed-halide perovskite, a solar cell retained 90% of its initial power conversion efficiency of 24.7% after 1000 hours of operation at approximately 40°C in nitrogen. —PDS

Circularly polarized luminescent (CPL) materials are currently attracting great interest. While a chiral building is usually necessary in order to obtain CPL materials, here, this study proposes a general approach for fabricating 1D circularly polarized luminescent nanoassemblies from achiral aromatic molecules or aggregation-induced emissive compounds (AIEgens). It is found that a C symmetric chiral gelator can individually form hexagonal nanotube structures and encapsulate the guest molecules. When achiral AIEgens are encapsulated into the confined nanotubes via organogelation, the AIEgens will emit circularly polarized luminescence. Further, the direction of the CPL could be controlled by the supramolecular chirality of the nanotube. Remarkably, the approach is universal and various kinds of the AIEgens can be doped to show such property, providing a full-color-tunable circularly polarized luminescence.

Amplification of circularly polarized luminescence (CPL) is demonstrated in a triplet-triplet annihilation-based photon upconversion (TTA-UC) system. When chiral binaphthyldiamine acceptors are sensitized with an achiral Pt(II) octaethylporphine (PtOEP) in solution, upconverted circularly polarized luminescence (UC-CPL) were observed for the first time, in which the positive or negative circularly polarized emission could be obtained respectively, following the molecular chirality of the acceptors (R/S). More interestingly, one order of magnitude amplification of the dissymmetry factor g in UC-CPL was obtained in comparison with the normal promoted CPL. The multistep photophysical process of TTA-UC including triplet-triplet energy transfer (TTET) and triplet-triplet annihilation (TTA) have been suggested to enhance the UC-CPL, which provided a new strategy to design CPL materials with a higher dissymmetry factor.

Metal halide perovskites have emerged as promising photovoltaic materials, but, despite ultralow thermal conductivity, progress on developing them for thermoelectrics has been limited. Here, we report the thermoelectric properties of all-inorganic tin based perovskites with enhanced air stability. Fine tuning the thermoelectric properties of the films is achieved by self-doping through the oxidation of tin (ΙΙ) to tin (ΙV) in a thin surface-layer that transfers charge to the bulk. This separates the doping defects from the transport region, enabling enhanced electrical conductivity. We show that this arises due to a chlorine-rich surface layer that acts simultaneously as the source of free charges and a sacrificial layer protecting the bulk from oxidation. Moreover, we achieve a figure-of-merit (ZT) of 0.14 ± 0.01 when chlorine-doping and degree of the oxidation are optimised in tandem.

While typical perovskite solar cells (PSCs) with doped Spiro-OMeTAD as hole transport material (HTM) have shown rapid increase in their power-conversion efficiencies (PCEs), their poor stability remains a big concern...

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%.