ZiQi Sun

Vapor-based deposition technique is considered as a promising approach for preparing a high-quality and uniform perovskite thin film. With evolution from coevaporation deposition to a low-pressure vapor-assisted solution process, both energy budget and reaction yield for perovskite film fabrications are improved. In this paper, a low-pressure hybrid chemical vapor deposition (LPHCVD) method is applied to fabricate CH₃NH₃PbI₃ perovskite films. The crucial dependence of working pressure on the perovskite formation is revealed. Moreover, the reaction time plays an important role in controlling the quality of the synthesized perovskite film. Efficient perovskite solar cells of 14.99% (mesoscopic), 15.37% (planar), and perovskite modules (active area of 8.4 cm²) of 6.22% are achieved by this LPHCVD method.

Highly efficient perovskite solar cells are made by low-pressure hybrid chemical vapor growth with superior uniformity. Small-area planar and mesoscopic devices obtain 15% power conversion efficiency with submodule of 6.22%.

The applications of organotin halide perovskites are limited because of their chemical instability under ambient conditions. Upon air exposure, Sn²⁺ can be rapidly oxidized to Sn⁴⁺, causing a large variation in the electronic properties. Here, the role of organic cations in degradation is investigated by comparing methylammonium tin iodide (MASnI₃) and formamidinium tin iodide (FASnI₃). Through chemical analyses and theoretical calculations, it is found that the organic cation strongly influences the oxidation of Sn²⁺ and the binding of H₂O molecules to the perovskite lattice. On the one hand, Sn²⁺ can be easily oxidized to Sn⁴⁺ in MASnI₃, and replacing MA with FA reduces the extent of Sn oxidation; on the other hand, FA forms a stronger hydrogen bond with H₂O than does MA, leading to partial expansion of the perovskite network. The two processes compete in determining the material's conductivity. It is noted that the oxidation is a difficult process to prevent, while the water effect can be largely suppressed by reducing the moisture level. As a result, FASnI₃-based conductors and photovoltaic cells exhibit much better reproducibility as compared to MASnI₃-based devices. This study sheds light on the development of stable Pb-free perovskite optoelectronic devices through new material design.

It is found that organic cation considerably influences the oxidation of Sn²⁺ and the binding of H₂O molecules to the perovskite lattice. Sn²⁺ can be easily oxidized to Sn⁴⁺ in MASnI₃, but not in FASnI₃. Solar cells fabricated from FASnI₃ demonstrate much improved reproducibility in device performance as compared to that from MASnI₃.

The light intensity dependence of the main photoelectrical parameters of the nonfullerene small-molecule bulk heterojunction (BHJ) solar cells p-DTS(FBTTh₂)₂:perylene diimide (T1:PDI) shows that the nongeminate recombination losses play an important role in this system. A simple approach for the quantitative analysis of capacitance spectroscopy data of the organic BHJ solar cells, which allows to determine the density of free charge carriers as a function of applied bias under standard working conditions, is demonstrated. Using the proposed capacitance spectroscopic technique, the nongeminate recombination losses in the T1:PDI solar cells are quantitatively characterized in the scope of the bimolecular- and trap-assisted recombination mechanisms. Their contributions are separately analyzed within a wide range of the applied bias.

A simple method for the determination of the density of free charge carriers and quantification of nongeminate recombination losses in organic-bulk heterojunction solar cells, based on the analysis of capacitance spectroscopy data, is presented. The proposed method is applied to the analysis of nongeminate recombination losses in nonfullerene T1: perylene diimide small-molecule solar cells in the scope of bimolecular- and trap-assisted recombination mechanisms under 1 sun illumination.

The role of the common stress factors such as high temperature, humidity, and UV irradiation on interface adhesion of roll-to-roll fabricated organic photovoltaic (OPV) devices is investigated. The samples range from bare front electrodes to complete devices. It is shown that applying single stress or combinations of stresses onto the samples variably affect the adhesion properties of the different interfaces in the OPV device. It is revealed that while the exposure of the complete devices to the stresses results in the loss of photovoltaic performance, some interfaces in the devices present improved adhesion properties. Depth profiling analysis on the fractured samples reveals interdiffusion of layers in the structure, which results in the increase of adhesion and change of the debond path. It is shown that through diffusion and intermixing of internal interfaces coupled stresses can increase the adhesion of OPV interfaces by over tenfold. The results are additionally compared to the photovoltaic performance of the complete devices.

The effect of high temperature, humidity, and UV irradiation on the interface adhesion of roll-to-roll fabricated organic photovoltaic (OPV) devices is investigated. The samples range from bare front electrodes to complete devices. It is shown that applying single stress or combinations of stresses onto the samples variably affects the adhesion properties of the different interfaces in the OPV device.

A novel fullerene cathode interlayer is employed to facilitate the fabrication of stable and efficient perovskite solar cells. This modified fullerene surfactant significantly increases air stability of the derived devices due to its hydrophobic characteristics to enable 80% of the initial PCE to be retained after being exposed in ambient condition with 20% relative humidity for 14 days.

An approach to fabricate high-efficiency inverted planar perovskites solar cells using solution-processed organic small molecules hole transporting layer is reported. Devices using CH₃NH₃PbI₃ as photoactive layer and PC₆₀BM as electron transport layer show power conversion efficiencies exceeding 12% and open-circuit voltages (V_OC) higher than 1 V.

Fullerene-free polymer solar cell devices based on a new acceptor, H-tri-PDI that is connected by three perylene diimide (PDI) units via imide position shows a power conversation efficiency of 7.25% with a short circuit current density of 16.5 mA cm⁻². Thus H-tri-PDI molecules and the method of connecting multiple PDI units via imide position provide a reliable guide for the further development of PDI-based acceptors.

In article number 1501929, Jia Xie, Lina Zhang, and co-workers present the construction of a hierarchical N/S-codoped carbon anode via a cost-effective and “green” route by pyrolyzing the cellulose/polyaniline composite microspheres. The micro-nanometer and atomic-level structure, designed via fabrication of the cellulose porous microspheres and N/S heteroatoms co-doping, ensures the carbon electrode an excellent rate capability and ultra-long cycle life in sodium-ion batteries, making it highly promising for large-scale energy storage applications.

Atomic-scale analyses represent oxygen-containing layers near grain boundaries in Cu₂ZnSnSe₄ films. In article number 1501902, Sung-Yoon Chung and co-workers identify the presence of nanoscale layers in which oxygen is substantially substituted for Se. Theoretical calculations demonstrate that oxygen substitution lowers the valence band maximum and thus makes a key contribution to the formation of a barrier blocking the holes from bulk grains.

The mechanism of light-induced degradation in organic solar cells based on regioregular poly(3-hexylthiophene) and indene-C₆₀ bisadduct is studied by transient absorption (TA) and electron spin resonance (ESR) measurements. After 45 h light exposure under simulated solar illumination at 100 mW cm⁻², the short-circuit current density, open-circuit voltage, and fill factor are all degraded by about 20%–30% relative to the initial photovoltaic parameters. For the assignment of limiting conversion processes in the degraded solar cells, exciton diffusion into a donor/acceptor interface, charge transfer at the interface, charge dissociation into free charge carriers, and charge collection to each electrode are observed before and after the light exposure by the TA measurement. As a result, it is found that the charge collection deteriorates after the light exposure because of light-induced charge trap formation in the bulk of the active layer. The origin of charge traps is further discussed on the basis of ESR measurements and density functional theory calculation.

Photodegradation mechanisms in regioregular poly(3-hexylthiophene) (P3HT)/indene-C₆₀ bisadduct blend cells are studied. Photovoltaic efficiency drops by ≈60% after 45 h solar cell operation. The origin of the photodegradation is attributed to charge trap formation in the P3HT disorder domains during the light exposure, likely because of residual bromine atoms at P3HT chain ends.

2D perovskites is one of the proposed strategies to enhance the moisture resistance, since the larger organic cations can act as a natural barrier. Nevertheless, 2D perovskites hinder the charge transport in certain directions, reducing the solar cell power conversion efficiency. A nanostructured mixed-dimensionality approach is presented to overcome the charge transport limitation, obtaining power conversion efficiencies over 9%.

A facile and effective “liquid knife” is created by controlling the dewetting process of the liquid precursor, yielding patterning single-crystalline perovskite microplates with uniform size, precise positioning, high quality, and low lasing thresholds. The sizes and location of single-crystalline perovskite are controllable, leading to mode-tunable lasing emission and patterned lasers.

Highly efficient utilization of solar light with an excellent reduction capacity is achieved for plasmonic Fe@C nanostructures. By carbon layer coating, the optimized catalyst exhibits enhanced selectivity and stability applied to the solar-driven reduction of CO₂ into CO. The surface-plasmon effect of iron particles is proposed to excite CO₂ molecules, and thereby facilitates the final reaction activity.

Incorporating carbon into Bi₃O₄Cl enhances its internal electric field by 126 times, which induces a bulk charge separation efficiency (η_bulk) of 80%. This ultrahigh η_bulk value presents a state-of-the-art result in tuning the bulk charge separation. The generated C-doped Bi₃O₄Cl has a noble-metal- and electron-scavenger-free water-oxidation ability under visible light, which is difficult to achieve with most existing photocatalysts.

Low-threshold two-photon-pumped (TPP) perovskite microcavity lasers are achieved in crystal perovskite 1D or 2D microstructures fabricated through a liquid-phase self-assembly method assisted by two distinct surfactant soft templates. The lasing actions from the perovskite materials exhibit a shape-dependent microcavity effect, which is subsequently utilized for the modulation of the lasing modes and for the achievement of two-photon-pumped single-mode perovskite microlasers.