Thermoelectric technology enables the harvest of waste heat and its direct conversion into electricity. The conversion efficiency is determined by the materials figure of merit Here we show a maximum of ~2.8 ± 0.5 at 773 kelvin in n-type tin selenide (SnSe) crystals out of plane. The thermal conductivity in layered SnSe crystals is the lowest in the out-of-plane direction [two-dimensional (2D) phonon transport]. We doped SnSe with bromine to make n-type SnSe crystals with the overlapping interlayer charge density (3D charge transport). A continuous phase transition increases the symmetry and diverges two converged conduction bands. These two factors improve carrier mobility, while preserving a large Seebeck coefficient. Our findings can be applied in 2D layered materials and provide a new strategy to enhance out-of-plane electrical transport properties without degrading thermal properties.

In this work, significant suppression of the interfacial recombination by facile alkali chloride interface modification of the NiOx hole transport layer in inverted planar perovskite solar cells is achieved. Experimental and theoretical results reveal that the alkali chloride interface modification results in improved ordering of the perovskite films, which in turn reduces defect/trap density, causing reduced interfacial recombination. This leads to a significant improvement in the open‐circuit voltage from 1.07 eV for pristine NiOx to 1.15 eV for KCl‐treated NiOx, resulting in a power conversion efficiency approaching 21%. Furthermore, the suppression of the ion diffusion in the devices is observed, as evidenced by stable photoluminescence (PL) under illumination and high PL quantum efficiency with alkali chloride treatment, as opposed to the luminescence enhancement and low PL quantum efficiency observed for perovskite on pristine NiOx. The suppressed ion diffusion is also consistent with improved stability of the devices with KCl‐treated NiOx. Thus, it is demonstrated that a simple interfacial modification is an effective method to not only suppress interfacial recombination but also to suppress ion migration in the layers deposited on the modified interface due to improved interface ordering and reduced defect density.

High thermoelectric performance of n-type PbTe is urgently needed to match its p-type counterpart. Here, we show a peak ZT ∼ 1.5 at 723 K and a record high average ZT > 1.0 at 300-873 K realized in n-type PbTe by synergistically suppressing lattice thermal conductivity and enhancing carrier mobility by introducing CuTe inclusions. Cu performs several outstanding roles: Cu atoms fill the Pb vacancies and improve carrier mobility, contributing to an unexpectedly high power factor of ∼37 μW cm K at 423 K; Cu atoms filling Pb vacancies and Cu interstitials both induce local disorder and, together with nano- and microscale Cu-rich precipitates and their related strain fields, lead to a very low lattice thermal conductivity of ∼0.38 Wm K in PbTe-5.5%CuTe, approaching the theoretical minimum value of ∼0.36 Wm K. This work provides an effective strategy to enhance thermoelectric performance by simultaneously improving electrical and thermal transport properties.

Both conductivity and mobility are essential to charge transfer by carrier transport layers (CTLs) in perovskite solar cells (PSCs). The defects derived from generally used ionic doping method lead to the degradation of carrier mobility and parasite recombinations. In this work, a novel molecular doping of NiO hole transport layer (HTL) is realized successfully by 2,2'-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6TCNNQ). Determined by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, the Fermi level (E ) of NiO HTLs is increased from -4.63 to -5.07 eV and valence band maximum (VBM)-E declines from 0.58 to 0.29 eV after F6TCNNQ doping. The energy level offset between the VBMs of NiO and perovskites declines from 0.18 to 0.04 eV. Combining with first-principle calculations, electrostatic force microscopy is applied for the first time to verify direct electron transfer from NiO to F6TCNNQ. The average power conversion efficiency of CsFAMA mixed cation PSCs is boosted by ≈8% depending on F6TCNNQ-doped NiOx HTLs. Strikingly, the champion cell conversion efficiency of CsFAMA mixed cations and MAPbI -based devices gets to 20.86% and 19.75%, respectively. Different from passivation effect, the results offer an extremely promising molecular doping method for inorganic CTLs in PSCs. This methodology definitely paves a novel way to modulate the doping in hybrid electronics more than perovskite and organic solar cells.

Dual-site point defects formed through partially dissolved Sb nanophases contribute to distortion of density-of-states and enhancement of phonon scattering.