Perovskite synthesis out in the open: Although methods have been developed that create the photoactive black perovskite phase of formamidinium lead iodide (α-FAPbI ₃ ), these routes are temperature and humidity sensitive and less compatible with large-scale solar cell production. Hui et al. report an alternative route in which vertically aligned lead iodide thin films are grown from the ionic liquid methylamine formate. Nanoscale channels in the films lower the barrier to permeation of formamidinium iodide and enable transformation to α-FAPbI ₃ , even at high humidity and room temperature. Solar cells made with these films have power conversion efficiencies as high as 24.1% that display high stability. Science , this issue p. 1359

Doping of bis(trifluoromethane)sulfonimide (LiTFSI) and 4-tert-butylpyridine (TBP) in 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) is currently considered irreplaceable for fabricating high-performance perovskite solar cells (PSCs). However, the stability of Spiro-OMeTAD was demonstrated to be seriously limited by the Li⁺ diffusion of LiTFSI and the volatilization of TBP. Herein, we report a strategy of doping with an organic molten salt, cyclohexylamine trifluoroacetic acid (CYTFA), to stabilize doped Spiro-OMeTAD for high-performance PSCs. We found that Li⁺ diffusion and TBP volatilization were effectively suppressed through strong interactions of dissociated CY⁺ and TFA⁻ acting on TBP and Li⁺. Moreover, CYTFA-doped Spiro-OMeTAD exhibits an order of magnitude increase in hole mobility and matched energy levels with perovskites. As a result, a solar cell with a power conversion efficiency of 25.80% was achieved, maintaining 96% and 80% of the initial efficiency for 500 hours at 55 °C and 55% humidity and for 470 hours at the maximum power point, respectively.

The lower charge mobility of organic semiconductors relative to that of inorganic semiconductors is a thorny problem that still has not been resolved. Here, a new type of arrangement of grid-shaped organic semiconductors with extremely low values of internal reorganization energies (IREs) for both hole (0.056 eV) and electron (0.078 eV) transfer processes has been designed and investigated by density functional theory (DFT) calculations. The structural, thermodynamic and electronic properties of grid spirofluorene (GSF) consisting of four spirobifluorenes have been discussed thoroughly. Our analyses of these unique grid structures indicate that they possess a stringent structure and very weak ring strain energy, and may be easily synthesized in the laboratory. Interestingly, GSF1, GSF2, and GSF9 possess both small hole and lower electron transfer reorganization energies (<0.1 eV), which may originate from their rigid molecular structures. The large π conjugated system in which all of the frontier molecular orbitals are homogeneously delocalized over the entire molecules is another important characteristic of these GSFs. This work reveals that the gridization method is a novel strategy for obtaining materials with low hole and electron transfer reorganization energies.

Atomic valence state regulation is an advantageous approach for improving photocatalytic efficiency and product selectivity. However, it is difficult to precisely control the ratio of the different valence states on the surface and the relationship between the surface valence change and catalytic efficiency in the photocatalytic reaction process is unclear. Herein, CeVO₄ ultrathin nanosheets were fabricated by one-step solvothermal method with ethanolamine (MEA) as the structure-directing agent. The ratio of the concentrations of intrinsic Ce⁴⁺ and Ce³⁺ ions is precisely modulated from 19.82:100 to 13.33:100 changed by the volume of MEA added without morphology modification. The photocatalytic efficiency increases as the concentrations of intrinsic Ce⁴⁺ and Ce³⁺ ions decrease and CV3 (prepared with 3 mL of MEA) shows the highest CO generation rate approximately 6 and 14 times larger than CV (prepared without MEA) and CV1 (prepared with 1 mL of MEA), respectively, in the photocatalytic CO₂ reduction. Interestingly, about 6.8% photo-induced Ce⁴⁺ ions were generated on the surface of the catalysts during the photocatalytic CO₂ reduction without any phase and morphology changes for CV3. The photocatalytic reaction mechanism is proposed considering the intrinsic and photo-induced Ce⁴⁺ ions to obtain efficient photocatalysts.