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A solvent-free solid-phase technique was developed for the targeted defect passivation of perovskite films, resulting in an ultra-high PCE of 25.2%.

A pre-embedding mixed A-cation halide strategy is developed to eliminate the residual unstable PbI2 and lattice strain near the buried interface of the perovskite layer for the stability improvement of formamidinium-based perovskite solar cells.

Electron acceptors with a chemical structure of A–DA′D–A (in which A denotes an acceptor moiety and D a donor moiety) are rapidly gaining prominence in organic solar cells (OSCs). In OSCs containing these acceptors, record power conversion efficiencies (PCEs) exceeding 16% are now widely reported. Despite encouraging advances related to new material designs and PCEs, the fundamental interplay between molecular structure and device performance still requires further understanding. Here, we choose two model A–DA′D–A type acceptors, Y3 and Y18, that have almost identical structures, and examine how the presence of two extra alkyl chains (attached to the periphery of the DA′D core) in Y18 impacts on its solid state properties and device performance. These properties include: (i) charge transport; (ii) heat transfer; and (iii) electronic disorder. We found that bulk-heterojunction (BHJ) OSCs that use Y3 and Y18 have markedly different PCEs of ∼13 and 16%, respectively. Correspondingly, the BHJ containing Y18 possesses more efficient phonon transfer and charge transport and suppressed electronic disorder. Among these properties, the extremely low Urbach energy (EU) of 23 meV in Y18 stands out because this is even below the thermal energy (∼26 meV), which sets the electronic disorder limit at room temperature. With all these contrasting results, a simple molecular model can be rationalized in which the extra alkyl chains in Y18 help to suppress the formation of rotamers, endowing it with a disorder free molecular conformation and remarkable solid state properties. This work provides not only a new physical understanding of the effect of alkyl chains in organic semiconductors, but also new ideas for the synthesis of novel materials that can be adopted for use in high-performance OSCs.

Defects play an important role in the degradation processes of hybrid halide perovskite absorbers, impeding their application for solar cells. Among all defects, halide anion and organic cation vacancies are ubiquitous, promoting ion diffusion and leading to thin-film decomposition at surfaces and grain boundaries. Here, we employ fluoride to simultaneously passivate both anion and cation vacancies, by taking advantage of the extremely high electronegativity of fluoride. We obtain a power conversion efficiency of 21.46% (and a certified 21.3%-efficient cell) in a device based on the caesium, methylammonium (MA) and formamidinium (FA) triple-cation perovskite (Cs0.05FA0.54MA0.41)Pb(I0.98Br0.02)3 treated with sodium fluoride. The device retains 90% of its original power conversion efficiency after 1,000 h of operation at the maximum power point. With the help of first-principles density functional theory calculations, we argue that the fluoride ions suppress the formation of halide anion and organic cation vacancies, through a unique strengthening of the chemical bonds with the surrounding lead and organic cations. Defects and defect migration are detrimental for perovskite solar cell efficiency and long-term stability. Li et al. show that fluoride is able to suppress the formation of halide anion and organic cation vacancy defects by restraining the relative ions via ionic and hydrogen bonds.

Pulsed laser deposition (PLD) is a powerful growth technique for thin films, where in situ doping and post-thermal annealing are the most effective ways to tune the crystalline and physical properties of the deposited films. This paper demonstrates that the crystallinity, transparency, and electrical properties of NiO films are well controlled by PLD, which determines the photovoltaic performance of CH3NH3PbI3−xClx-based perovskite solar cells with NiO films as the hole transport layers (HTLs). After post-annealing, the NiO films exhibit enhanced in-plane crystal orientation, high transmittance, and uniform surface morphology, and, accordingly, the power conversion efficiency (PCE) of the perovskite solar cell improves from 5.38% to 12.59%. Moreover, by doping the ablated target with lithium (Li), PLD can produce doped NiO:Li films with significantly enhanced electrical conductivity, which further improves the perovskite cell PCE from 12.59% to 15.51%. These results highlight the importance of optimizing the transporting layer properties toward high-performance inverted perovskite planar solar cells.

A fused-ring electron acceptor based on indacenodithiophene (IDIC) was used to replace TiO2 and work as an electron transport layer in planar n–i–p perovskite solar cells. IDIC improves perovskite crystallinity and film quality due to its hydrophobicity and incompatible wetting surface. IDIC facilitates electron extraction and transport due to its high mobility and suitable energy levels matched with the perovskite. IDIC reduces charge recombination in the devices due to trap passivation at the perovskite surface. The IDIC-based devices exhibit a champion power conversion efficiency of 19.1%, which is higher than that of TiO2-based devices (17.4%). Moreover, the device stability is significantly improved by IDIC.

Pentacene thin film on CH3NH3PbI3 was studied by in-situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy to determine their interfacial energy level alignment. A 0.2 eV downward band bending together with a 0.1 eV interfacial dipole was found at the pentacene side, whereas there was no band bending found at the CH3NH3PbI3 side. The offset between CH3NH3PbI3 Valance Band Maximum (VBM) and pentacene Highest Occupied Molecular Orbital (HOMO) and that between CH3NH3PbI3 Conduction Band Minimum (CBM) and pentacene Lowest Unoccupied Molecular Orbital (LUMO) was determined to be 0.7 and 1.35 eV, respectively. The band alignment at this interface is favor of efficient hole transfer, which suggests pentacene as a viable HTL candidate to be explored in perovskite solar cells.

Hybrid organic–inorganic perovskite materials offer a range of interesting characteristics that are suitable for optoelectronic devices, such as photovoltaics. Along with the fast rise in device performance, a current density–voltage (J–V) hysteresis originating from defects and their movement has attracted intense attention, which renders challenges regarding the stability and reliability of the novel materials. Here, we carefully probe the effects of defects in perovskite materials and across interfaces within the device, in which bistable conductive states are achieved for the next generation of nonvolatile memory. The memory device shows an operating voltage as low as 0.25 V, and a decent ON/OFF ratio. More importantly, we correlate the defect density and hysteresis-index of different perovskite films with the corresponding memory device performance. The findings enrich our understanding of the working mechanism of perovskite memory devices, which will also benefit other organic–inorganic hybrid perovskite optoelectronics.

We systematically investigated the impact of stoichiometric ratio variation between PbX

The design of electron transport layers (ETLs) is crucial to the performance of optoelectronic devices. A composite ETL was constructed to overcome the poor carrier extraction issue in perovskite solar cells, resulting in a maximum PCE of 19.14% with reduced hysteresis. A similar enhancement phenomenon was observed in both devices based on TiO2 and SnO2 ETLs.

Correction for ‘A disorder-free conformation boosts phonon and charge transfer in an electron-deficient-core-based non-fullerene acceptor’ by Chujun Zhang et al., J. Mater. Chem. A, 2020, 8, 8566–8574, DOI: 10.1039/d0ta01260b.

The electronic structures of rubrene films deposited on CH

Engineering the chemical composition of organic and inorganic hybrid perovskite materials is one of the most feasible methods to boost the efficiency of perovskite solar cells with improved device stability. Among the diverse hybrid perovskite family of ABX

A high‐mobility p‐type organic semiconductor based on benzodithiophene and diketopyrrolopyrrole with linear alkylthio substituents (BDTS‐2DPP) is used as a dual function interfacial layer to modify the interface of perovskite/2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene in planar perovskite solar cells. The BDTS‐2DPP layer can remarkably passivate the surface defects of perovskite through the formation of Lewis adduct between the under‐coordinated Pb atoms in perovskite and S atoms in BDTS‐2DPP, and also shows efficient hole extraction and transfer properties. The devices with BDTS‐2DPP interlayer show a peak power conversion efficiency of 18.2%, which is higher than that of reference devices without the BDTS‐2DPP interlayer (16.9%). Moreover, the hydrophobic BDTS‐2DPP interlayer effectively protects the perovskite against moisture, leading to enhanced device stability.