Influence of Donor Skeleton on Intramolecular Electron Transfer Amount for Efficient Perovskite Solar Cells.

The passivation of the defects derived from rapid-crystallization with electron-donating molecules is always a prerequisite to obtain desirable perovskite films for efficient and stable solar cells, thus, the in-depth understanding on the correlations between molecular structure and passivation capacity is of great importance for screening passivators. Here, we introduce the double-ended amide molecule into perovskite precursor solution to modulate crystallization process and passivate defects. By regulating the intermediate bridging skeletons with alkyl, alkenyl and benzene groups, the results show the passivation strength highly depends on the spin-state electronic structure that serves as an intrinsic descriptor to determine the intramolecular charge distribution by controlling orbital electron transfer from the donor segment to acceptor segment. Upon careful optimization, the benzene-bridged amide molecule demonstrates superior efficacy on improving perovskite film quality. As a physical proof-of-concept, the carbon-based, all-inorganic CsPbI2Br solar cell delivers a significantly increased efficiency of 15.51 % with a remarkably improved stability. Based on the same principle, a champion efficiency of 24.20 % is further obtained on the inverted (Cs0.05MA0.05FA0.9)Pb(I0.93Br0.07)3 solar cell. These findings provide new fundamental insights into the influence of spin-state modulation on effective perovskite solar cells.

Healing the Buried Interface by a Plant-Derived Green Passivator for Carbon-Based CsPbIBr2 Perovskite Solar Cells.

Perovskite solar cells (PSCs) have attracted extensive attention in photovoltaic applications owing to their superior efficiency, and the buried interface plays a significant role in determining the efficiency and stability of PSCs. Herein, a plant-derived small molecule, ergothioneine (ET), is adopted to heal the defective buried interface of CsPbIBr2-based PSC to improve power conversion efficiency (PCE). Because of the strong interaction between Lewis base groups (-C═O and -C═S) in ET and uncoordinated Pb2+ in the perovskite film from the theoretical simulations and experimental results, the defect density of the CsPbIBr2 perovskite film is significantly reduced, and therefore, the nonradiative recombination in the corresponding device is simultaneously suppressed. Consequently, the target device achieves a high PCE of 11.13% with an open-circuit voltage (VOC) of 1.325 V for hole-free, carbon-based CsPbIBr2 PSCs and 14.56% with a VOC of 1.308 V for CsPbI2Br PSCs. Furthermore, because of the increased ion migration energy, the detrimental phase segregation in this mixed-halide perovskite is weakened, delivering excellent long-term stability for the unencapsulated device in ambient conditions over 70 days with a 96% retention rate of initial efficiency.

Self-powered PtNi-polyaniline films for converting rain energy into electricity.

Developing novel rainwater energy harvesting beyond conventional electricity is a promising strategy to address the problems of the energy crisis and environmental pollution. In this current work, a class of self-powered PtNi and optimal PtNi-polyaniline (PANI) films are successfully developed to convert rainwater into electricity for power generation. The maximized current, voltage and power of the self-powered PtNi-PANI films are 4.95 µA per droplet, 69.85 µV per droplet and 416.54 pW per droplet, respectively, which are attributed to the charging/discharging electrical signals between the cations provided by the rainwater and the electrons offered by the films. These results indicate that the optimized signal values are highly dependent on the elevated electron concentration of films, as well as the concentration, radius and charge of ions in rainwater. This work provides fresh insights into rain energy and enriches our knowledge of how to convert renewable energy into electricity generation.

Liquid buried interface to slide lattice and heal defects in inorganic perovskite solar cells.

The residual tensile strain, which is induced by lattice and thermal expansion coefficient difference between upper perovskite film and underlying charge transporting layer, significantly deteriorates the power conversion efficiency (PCE) and stability of a halide perovskite solar cell (PSC). To overcome this technical bottleneck, herein, we propose a universal liquid buried interface (LBI) by introducing a low melting-point small molecule to replace traditional solid-solid interface. Arising from the movability upon solid-to-liquid phase conversion, LBI plays a role of "lubricant" to effectively free the soft perovskite lattice shrinkage or expansion rather than anchoring onto the substrate, leading to the reduced defects due to the healing of strained lattice. Finally, the inorganic CsPbIBr2 PSC and CsPbI2Br cell achieve the best PCEs of 11.13 % and 14.05 %, respectively, and the photo-stability is improved by 33.3-fold because of the suppressed halide segregation. This work provides new insights on the LBI for making high-efficiency and stable PSC platforms.

In situ formation of inorganic healing overlayer for interface-stabilized all-inorganic CsPbIBr2 perovskite solar cells.

A perovskite layer functionalized to be an outermost screen can strongly affect the capacity of the underlying device to avoid becoming decomposed under external stimuli, and subsequently affect the photovoltaic performance as well. Herein, we report an interface-stabilization strategy for an all-inorganic CsPbIBr2 film involving forming in situ an inorganic ZrO2 layer to solidify the soft perovskite lattice. As a result of defect passivation and self-encapsulation, the best device achieved an enhanced efficiency of up to 10.12%, which was much higher than the 7.47% efficiency for the reference device tested, with prolonged stability under conditions of persistent light irradiation and exposure to air.

Universal Dynamic Liquid Interface for Healing Perovskite Solar Cells.

Healing charge-selective contact interfaces in perovskite solar cells (PSCs) highly determines the power conversion efficiency (PCE) and stability. However, the state-of-the-art strategies are often static by one-off formation of a functional interlayer, which delivers fixed interfacial properties during the subsequent operation. As a result, defects formed in-service will gradually deteriorate the photovoltaic performances. Herein, a dynamic healing interface (DHI) is presented by incorporating a low-melting-point small molecule onto perovskite film surface for highly efficient and stable PSCs. Arising from the reduced non-radiative recombination, the DHI boosts the PCE to 12.05% for an all-inorganic CsPbIBr2 solar cell and 14.14% for a CsPbI2 Br cell, as well as 23.37% for an FA0.92 MA0.08 PbI3 (FA = formamidinium, MA = methylammonium) cell. The solid-to-liquid phase conversion of DHI at elevated temperature causes a longitudinal infiltration into the bulk perovskite film to maximize the charge extraction, passivate defects at grain boundaries, and suppress ion migration. Furthermore, the stability is remarkably enhanced under air, heat, and persistent light-irradiation conditions, paving a universal strategy for advanced perovskite-based optoelectronics.

Thermal-Triggered Dynamic Disulfide Bond Self-Heals Inorganic Perovskite Solar Cells.

One great challenge for perovskite solar cells (PSCs) lies in their poor operational stability under harsh stimuli by humidity, heat, light, etc. Herein, a thermal-triggered self-healing polyurethane (PU) is tailored to simultaneously improve the efficiency and stability of inorganic CsPbIBr2 PSCs. The dynamic covalent disulfide bonds between adjacent molecule chains in PU at high temperatures self-heal the in-service formed defects within the CsPbIBr2 perovskite film. Finally, the best device free of encapsulation achieves a champion efficiency up to 10.61 % and an excellent long-term stability in an air atmosphere over 80 days and persistent heat attack (85 °C) over 35 days. Moreover, the photovoltaic performances are recovered by a simple heat treatment.

Tailored Lattice "Tape" to Confine Tensile Interface for 11.08%-Efficiency All-Inorganic CsPbBr3 Perovskite Solar Cell with an Ultrahigh Voltage of 1.702 V.

The crystal distortion such as lattice strain and defect located at the surfaces and grain boundaries induced by soft perovskite lattice highly determines the charge extraction-transfer dynamics and recombination to cause an inferior efficiency of perovskite solar cells (PSCs). Herein, the authors propose a strategy to significantly reduce the superficial lattice tensile strain by means of incorporating an inorganic 2D Cl-terminated Ti3 C2 (Ti3 C2 Clx ) MXene into the bulk and surface of CsPbBr3 film. Arising from the strong interaction between Cl atoms in Ti3 C2 Clx and the under-coordinated Pb2+ in CsPbBr3 lattice, the expanded perovskite lattice is compressed and confined to act as a lattice "tape", in which the PbCl bond plays a role of "glue" and the 2D Ti3 C2 immobilizes the lattice. Finally, the defective surface is healed and a champion efficiency as high as 11.08% with an ultrahigh open-circuit voltage up to 1.702 V is achieved on the best all-inorganic CsPbBr3 PSC, which is so far the highest efficiency record for this kind of PSCs. Furthermore, the unencapsulated device demonstrates nearly unchanged performance under 80% relative humidity over 100 days and 85 °C over 30 days.

Defect Control Strategy by Bifunctional Thioacetamide at Low Temperature for Highly Efficient Planar Perovskite Solar Cells.

Titania (TiO2) has wide applications in the realm of perovskite solar cells (PSCs). Because high-temperature processing severely limits the application of flexible and tandem devices, it is significant to develop a high-quality electron-transport layer (ETL) by low-temperature processing. Here, we design a new strategy by introducing a bifunctional molecule (thioacetamide, TAA) in the TiO2 ETL. During the low-temperature annealing, the N and S atoms in TAA can bond with the Ti atom in the ETL and the Pb atom in the perovskite (PVK) layer, respectively. The formation of coordinate bonds is beneficial to increase the crystallinity and reduce the roughness of TiO2 ETLs and PVK layers, which effectively passivate the defects. Meanwhile, the energy level matching between the ETL and PVK is optimized. The structure characterization and electrochemical measurement demonstrate the design. Compared with precursor doping, surface spin-coating is a more effective method for introducing TAA into TiO2. Significantly, the PSC based on the surface spin-coated TAA TiO2 ETL achieves the best power conversion efficiency (PCE) of 21.17%. Nevertheless, the PSC fabricated with the pristine TiO2 ETL offers a PCE of 19.52% under the same conditions. The results demonstrate a novel method for optimizing the properties of PSCs.

Suppressing Vacancy Defects and Grain Boundaries via Ostwald Ripening for High-Performance and Stable Perovskite Solar Cells.

As one kind of promising next-generation photovoltaic devices, perovskite solar cells (PVSCs) have experienced unprecedented rapid growth in device performance over the past few years. However, the practical applications of PVSCs require much improved device long-term stability and performance, and internal defects and external humidity sensitivity are two key limitation need to be overcome. Here, gadolinium fluoride (GdF3 ) is added into perovskite precursor as a redox shuttle and growth-assist; meanwhile, aminobutanol vapor is used for Ostwald ripening in the formation of the perovskite layer. Consequently, a high-quality perovskite film with large grain size and few grain boundaries is obtained, resulting in the reduction of trap state density and carrier recombination. As a result, a power conversion efficiency of 21.21% is achieved with superior stability and negligible hysteresis.

High-Performance and Hysteresis-Free Perovskite Solar Cells Based on Rare-Earth-Doped SnO2 Mesoporous Scaffold.

Tin oxide (SnO2), as electron transport material to substitute titanium oxide (TiO2) in perovskite solar cells (PSCs), has aroused wide interests. However, the performance of the PSCs based on SnO2 is still hard to compete with the TiO2-based devices. Herein, a novel strategy is designed to enhance the photovoltaic performance and long-term stability of PSCs by integrating rare-earth ions Ln3+ (Sc3+, Y3+, La3+) with SnO2 nanospheres as mesoporous scaffold. The doping of Ln promotes the formation of dense and large-sized perovskite crystals, which facilitate interfacial contact of electron transport layer/perovskite layer and improve charge transport dynamics. Ln dopant optimizes the energy level of perovskite layer, reduces the charge transport resistance, and mitigates the trap state density. As a result, the optimized mesoporous PSC achieves a champion power conversion efficiency (PCE) of 20.63% without hysteresis, while the undoped PSC obtains an efficiency of 19.01%. The investigation demonstrates that the rare-earth doping is low-cost and effective method to improve the photovoltaic performance of SnO2-based PSCs.

An efficient solvent additive for the preparation of anion-cation-mixed hybrid and the high performance perovskite solar cells.

Lead amine halide perovskite solar cells have been dominating photovoltaic research in this decade. The quality of the perovskite layer plays a significant role in the photovoltaic performance of planar perovskite devices, and solvent engineering is an effective method to improve the quality of the perovskite layer. Here, we introduce acetonitrile (ACN) as an effective solvent additive in the preparation of cation-anion-mixed perovskite of Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3. The morphology observation indicates that a large grain, compact and pinhole-free perovskite layer is obtained by ACN adding. Steady-state and time-resolved photoluminescence measurements demonstrate fewer defects and less carrier recombination in the perovskite layer with ACN adding. The planar perovskite solar cell with ACN adding achieves a power conversion efficiency of 19.15% with slight hysteresis and stable output, while the device without ACN adding gets an efficiency of 17.47% under the same experiment conditions. The simple and green preparation process and the significant improvement of the device performance render this method promising.