Dual Defect Passivation at the Buried Interface for Printable Mesoscopic Perovskite Solar Cells with Reduced Open-Circuit Voltage Loss.

Numerous defects exist at the buried interface between the perovskite and adjacent electron transport layers in perovskite solar cells, resulting in severe non-radiative recombination and excessive open-circuit voltage (VOC) loss. Herein, a dual defect passivation strategy utilizing guanidine sulfate (GUA2SO4) as an interface modifier is first reported. On the one hand, the SO4 2- preferentially interacts with Pb-related defects, generating water-insoluble lead oxysalts complexes. Additionally, GUA+ diffuses into the perovskite and induces the formation of low-dimensional perovskite. These reactions effectively suppress trap states at the buried interface and perovskite boundaries in printable mesoscopic perovskite solar cells (p-MPSCs), thus increasing the carrier lifetime. Meanwhile, GUA2SO4 optimizes the interface energy band alignment, thus accelerating the charge extraction and transfer at the buried interface. This synergistic effect of trap passivation and interface energy band alignment modulation is strongly demonstrated by an increase in average VOC of 70 mV and the power conversion efficiency improvement from 17.51% to 18.70%. This work provides a novel approach to efficiently improve the performance of p-MPSCs through dual-targeted defect passivation at the buried interface.

Record-Efficiency Printable Hole-Conductor-Free Mesoscopic Perovskite Solar Cells Enabled by the Multifunctional Schiff Base Derivative.

Tailoring multifunctional additives for performing interfacial modifications, improving crystallization, and passivating defects is instrumental for the fabrication of efficient and stable perovskite solar cells (PSCs). Here, a Schiff base derivative, (chloromethylene) dimethyliminium chloride (CDCl), is introduced as an additive to modify the interface between the mesoporous TiO2 electron transport layer and the MAPbI3 light absorber during the annealing process. CDCl chemically links to TiO2 and MAPbI3 through coordination and hydrogen bonding, respectively, and results in the construction of fast electron extraction channels. CDCl also optimizes the energy-level alignment of the TiO2/MAPbI3 heterojunction and improves the pore-filling and crystallization of MAPbI3 in the mesoscopic scaffold, which inhibits nonradiative recombination and eliminates open-circuit voltage losses. As a result, an impressive power conversion efficiency of 19.74%, which is the best one ever reported, is obtained for printable carbon-based hole-conductor-free PSCs based on MAPbI3.

Electron injection and defect passivation for high-efficiency mesoporous perovskite solar cells.

Printable mesoscopic perovskite solar cells (p-MPSCs) do not require the added hole-transport layer needed in traditional p-n junctions but have also exhibited lower power conversion efficiencies of about 19%. We performed device simulation and carrier dynamics analysis to design a p-MPSC with mesoporous layers of semiconducting titanium dioxide, insulating zirconium dioxide, and conducting carbon infiltrated with perovskite that enabled three-dimensional injection of photoexcited electrons into titanium dioxide for collection at a transparent conductor layer. Holes underwent long-distance diffusion toward the carbon back electrode, and this carrier separation reduced recombination at the back contact. Nonradiative recombination at the bulk titanium dioxide/perovskite interface was reduced by ammonium phosphate modification. The resulting p-MPSCs achieved a power conversion efficiency of 22.2% and maintained 97% of their initial efficiency after 750 hours of maximum power point tracking at 55 ± 5°C.

Stratified Oxygen Vacancies Enhance the Performance of Mesoporous TiO2 Electron Transport Layer in Printable Perovskite Solar Cells.

The low electrical conductivity and the high surface defect density of the TiO2 electron transport layer (ETL) limit the power conversion efficiency (PCE) of corresponding perovskite solar cells (PSCs). Here, the conductivity and defect modulation of the mesoporous TiO2 (mp-TiO2 ) ETL via oxygen vacancy (OV) management by the reduction and oxidation treatment are reported. Reduction treatment via reducing agent introduces abundant OVs into the TiO2 nanocrystalline particles on the surface and at the subsurface. The following oxidation treatment via hydrogen peroxide removes the surface OVs while remains the subsurface OVs, resulting in stratified OVs. The stratified OVs improve the conductivity of TiO2 ETL by increasing carrier donors and decrease nonradiative centers by reducing surface defects. Such synergy ensures the capability of mp-TiO2 as the well-performed ETL with improved energy level alignment, suppressed interface recombination, enhanced carrier extraction, and transport. As a result, printable hole-conductor-free carbon-based mesoscopic PSCs based on the modulated mp-TiO2 ETL demonstrate a highest reported PCE of 18.96%.

Halide Perovskite Crystallization Processes and Methods in Nanocrystals, Single Crystals, and Thin Films.

Halide perovskite semiconductors with extraordinary optoelectronic properties have been fascinatedly studied. Halide perovskite nanocrystals, single crystals, and thin films have been prepared for various fields, such as light emission, light detection, and light harvesting. High-performance devices rely on high crystal quality determined by the nucleation and crystal growth process. Here, the fundamental understanding of the crystallization process driven by supersaturation of the solution is discussed and the methods for halide perovskite crystals are summarized. Supersaturation determines the proportion and the average Gibbs free energy changes for surface and volume molecular units involved in the spontaneous aggregation, which could be stable in the solution and induce homogeneous nucleation only when the solution exceeds a required minimum critical concentration (Cmin ). Crystal growth and heterogeneous nucleation are thermodynamically easier than homogeneous nucleation due to the existent surfaces. Nanocrystals are mainly prepared via the nucleation-dominated process by rapidly increasing the concentration over Cmin , single crystals are mainly prepared via the growth-dominated process by keeping the concentration between solubility and Cmin , while thin films are mainly prepared by compromising the nucleation and growth processes to ensure compactness and grain sizes. Typical strategies for preparing these three forms of halide perovskites are also reviewed.

van der Waals Mixed Valence Tin Oxides for Perovskite Solar Cells as UV-Stable Electron Transport Materials.

Stable electron transport materials (ETMs) with fewer surface defects and proper energy level alignments with halide perovskite active layers are required for efficient perovskite solar cells (PSCs) with long-term durability. Here, two-dimensional van der Waals mixed valence tin oxides Sn2O3 and Sn3O4 are controllably synthesized and applied as ETMs for planar PSCs. The synthesized Sn2O3 and Sn3O4 have size of 5-20 nm and disperse well in water as stable colloids for months. Both Sn2O3 and Sn3O4 exhibit typical n-type semiconductor energy band structures, low trap density, and suitable energy level alignments with halide perovskites. Steady-state power conversion efficiencies (PCEs) of 22.36% and 21.83% are obtained for Sn2O3-based and Sn3O4-based planar PSCs. In addition, the half cells without hole transport materials and back electrodes show good UV-stability with average PCE of 99.0% and 95.7% for Sn2O3-based and Sn3O4-based devices remaining after 1000 h of ultraviolet soaking with an intensity of 70 mW cm-2.

[Optimized expression and functional analysis of enhancin gene from Pseudaletia unipuncta granulovirus (PuGV-Ps)].

Objective: To explore the feasibility of using enhancin as synergist to Bacillus thuringiensis (Bt), the truncated fragments of enhancin gene from Pseudaletia unipuncta granulovirus (PuGV-Ps) were optimized and the enhancing effects were studied. Methods: Based on bioinformational analysis of the function domain of PuGV-Ps enhancin, the prokaryotic expression vectors were constructed, and the protein expression levels as well as their enhancing effects on the degradation of peritrophic membrane (PM) proteins were analyzed, and the function domains of PuGV-Ps enhancin were confirmed. Results: Three domains were found in the enhancin of PuGV-Ps, including M60-like domain, Zincins catalytic domain and putative mucin or carbohydrate-binding domain. Thirteen predicted N-glycosylation sites were also identified. Based on the sequences of truncated M60-like domain (P69) and carbohydrate-binding domain (P77), two expression vectors, pET15b-P69 and pET15b-P77, were constructed. The expressed P69 and P77 abundance were higher than that of full length enhancing (P104). The degradation activity of purified P69 on the PM proteins of Spodoptera litura was higher than that of purified P77, but both showed lower degradation activities than P104. Both P69 and P77 improved the toxicity of Bt against larvae of Plutella xylostella. However, their synergistic effects were significantly lower than that of P104. Conclusion: The results revealed that the M60-like domain in N-terminus and carbohydrate-binding domain in C-terminus of PuGV-Ps enhancin all contributed to the enhancing effects of enhancin as well as the maintenance of its native conformation. The truncated P69 fragment may function in keeping the activity of enhacin and improving prokaryotic expression levels. These results provide some useful guidance for the industrialized production of enhancin.

[Effect of Bacillus thuringiensis var. israelensis (Bti) on detoxification enzyme activity of larvae of Culex pipiens pallens and Aedes aegypti].

OBJECTIVE: To investigate the effect of Bacillus thuringiensis var. israelensis (Bti) on the activities of three detoxification enzymes of Culex pipiens pallens and Aedes aegypti larvae. METHODS: The activities of glutathione transferase, acetyl cholinesterase and carboxyl esterase, were detected after two kinds of mosquito larvae were treated by Bti at different time and concentrations. RESULTS: The activities of three detoxification enzymes of the two kinds of mosquito larvae were influenced by Bti treatment. The activity of glutathione transferase was increased after the Bti treatment, but declined significantly and inhibited at a low level sustainably. The activity of carboxyl esterase was increased after the Bti treatment, but recovered to normal level quickly. Acetyl cholinesterase was affected slightly by the Bti treatment, shortly inhibited in the first time and then recovered. The active effects of the three detoxification enzymes were positively related to the concentration of Bti. CONCLUSION: The enzyme activities of glutathione transferase, acetyl cholinesterase and carboxyl esterase could be affected by Bti significantly.

[Characterization of Bacillus thuringrensis var. israelesis larvicide granules to larvae of mosquitoes].

OBJECTIVE: To develop a new formulation of Bacillus thuringrensis var. israelesis (Bti) granules and assess its effect on mosquito control. METHODS: The Bti granule formulation was produced by coating Bti liquid on the surface of the carrier. and imitation tests, persistence tests and field tests were carried to assess its mosquito larvicidal effect, extended period and stability. RESULTS: A strain of Bti isolated from field had high toxicity to mosquito larvae and its LC50 values for larvae of Culex pipiens pallens and Aedes aegypti were 0.461 0 microl/L and 1.713 3 microl/L respectively. The developed 216 ITU/mg Bti granules had a control effect of 83.3%-100% to larvae of C. pipiens pallens at the dosage of 1-3 g/m2, and 72.7%-100% to A. aegypti at the dosage of 3-5 g/m2. When the 3rd instar larvae of C. pipiens pallens were put in the water that was treated with the granules at the dosage of 0.5 g/m2 13 days before, the larval mortality still reached to 55.3%. The field tests showed that with the treatment of 2-4 g/m2 Bti granules, the control effects on the larvae were high from 92.4% to 100% within the first 3 days and about 51.6%-75.7% after 20 days. CONCLUSION: The developed new formulation of Bti granules with the isolated strain has a preferable control effect on mosquito larvae and reveals a longer persistence and better stability than liquid formulation in the field tests.