Natural Antioxidant Vitamin C Improves Photovoltaic Performance of Tin-Lead Mixed Perovskite Solar Cells.

The oxidation of Sn2+ can occur even after the completion of the perovskite crystallization in a low oxygen environment. Concerning this, the natural antioxidant vitamin C (VC) is introduced to the surface of Sn-Pb mixed perovskite using a postprocessing method to achieve the purpose of inhibiting Sn2+ oxidation and enhancing perovskite solar cells performance. The results indicate that the VC could effectively inhibit Sn2+ oxidation and heal the vacancy defects of the annealed perovskite film. Meanwhile, the introduction of VC significantly improves the morphology and crystalline quality of the perovskite films. After optimization, the highest power conversion efficiency of the VC-treated Sn-Pb mixed device increased to 20.44%. Moreover, the VC-treated unencapsulated device shows excellent long-term stability, retaining 75.3% of its initial efficiency after 800 h of aging in a N2 atmosphere, which is much higher than the 20.1% of the control device.

Efficient and Stable Tin-Lead Mixed Perovskite Solar Cells Using Post-Treatment Additive with Synergistic Effects.

Inhibiting the oxidation of Sn2+ during the crystallization process of Sn-Pb mixed perovskite film is found to be as important as the oxidation resistance of precursor solution to achieve high efficiency, but less investigated. Considering the excellent reduction feature of hydroquinone and the hydrophobicity of tert-butyl group, an antioxidant 2,5-di-tert-butylhydroquinone (DBHQ) was introduced into Sn-Pb mixed perovskite films using an anti-solvent approach to solve this problem. Interestingly, we find that DBHQ can act as function alterable additive during its utilization. On the one hand, DBHQ can restrict the oxidation of Sn2+ during the crystallization process, facilitating the fabrication of high-quality perovskite film; on the other hand, the generated oxidation product 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) can functionalize as defect passivator to inhibit the charge recombination. As a result, this synergetic effect renders the Sn-Pb mixed PSC a power conversion efficiency (PCE) up to 23.0 %, which is significantly higher than the reference device (19.6 %). Furthermore, the unencapsulated DBQH-modified PSCs exhibited excellent long-term stability and thermal stability, with the devices maintaining 84.2 % and 78.9 % of the initial PCEs after aging at 25 °C and 60 °C for 800 h and 120 h under N2 atmosphere, respectively. Therefore, the functional alterable strategy provides a novel cornerstone for high-performance Sn-Pb mixed PSCs.

Asymmetric Small Molecule as Interface "Governor" for FAPbI3 Perovskite Solar Cells.

Delicate interface modification is necessary for improving the photovoltaic performance of a perovskite solar cell (PSC). Herein, two asymmetric small molecules, termed BTD-DA and BTD-PA are designed and synthesized to govern the perovskite/Spiro-OMeTAD interface. The molecule BTD-PA featuring a donor-acceptor-acceptor (D-A-A') configuration shows a larger molecule dipole and a better effect on defect passivation and energy level regulation through the strong interaction between the pyridine group in BTD-PA and the surficial uncoordinated Pb2+. Consequently, the PSCs based on the BTD-PA treatment harvest a champion power conversion efficiency (PCE) of 24.46% for a 0.09 cm2 active area and 22.46% for the 1 cm2 device. Moreover, the long-term stability of FAPbI3 PSCs is also significantly improved because of the enhanced hydrophobicity and the inhibited phase transition of the FAPbI3 film with BTD-PA treatment. Our research provides a new strategy for interfacial engineering to boost the PCE and stability of the FAPbI3 PSCs.

Molecular Engineering of Peripheral Substitutions to Construct Efficient Acridine Core-Based Hole Transport Materials for Perovskite Solar Cells.

The development of highly efficient hole transport materials (HTMs) for perovskite solar cells (PSCs) has been a hot research topic. Acridine and its derivatives are gradually utilized as new blocks for optoelectronic applications, which stems from its rigid conjugated structure, shedding a new light on this old molecule. Meanwhile, its application in PSCs as a HTM has not been well explored, and the efficiency of 9,10-dihydroacridine (ACR)-based HTMs is relatively low. In this work, we conduct a systematic modulation of the peripheral substituents for ACR core building block-based HTMs and investigate the effects of the electron-donating ability and π-conjugation of peripheral groups on the photovoltaic performance of the corresponding HTMs. It is found that the peripheral groups with a weaker electron-donating ability and stronger π-conjugation are more suitable for the acridine core, which itself has a stronger electron-donating ability. Through molecular engineering, the newly developed HTM ACR-PhDM achieves an impressive power conversion efficiency of 23.5%. Our work lays the foundation for the design and development of efficient HTMs in the future.

Bi(trifluoromethyl) Benzoic Acid-Assisted Shallow Defect Passivation for Perovskite Solar Cells with an Efficiency Exceeding 21.

Chemical additive engineering is reported to be a simple yet effective approach to passivate shallow defects at the surface and grain boundaries, restrict nonradiative recombination losses, and further enhance the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, we successfully introduce a small organic molecule 3,5-bis(trifluoromethyl)benzoic acid (6FBzA) into an antisolvent as a shallow defect passivator for perovskite films. The Pb2+ defects at the surface are greatly healed due to the coordination interaction of carbonyl and fluorine groups of 6FBzA with Pb2+. Consequently, the trap-assisted nonradiative recombination is effectively suppressed, as well as the interfacial charge extraction and transfer is significantly enhanced. As a result, the 6FBzA-treated PSC obtains a champion PCE of 21.09% with negligible hysteresis, which is obviously superior to the reference device (18.45%). Furthermore, on account of the high hydrophobicity of 6FBzA, the unencapsulated 6FBzA-treated device exhibits a good long-term stability, maintaining 82% of its initial PCE at a relative humidity of 30-40% in ambient air after 1800 h of aging.

Surface Defect Passivation and Energy Level Alignment Engineering with a Fluorine-Substituted Hole Transport Material for Efficient Perovskite Solar Cells.

The surface and boundary defects present in the perovskite film are reported to be nonradiative recombination and degradation centers, restricting further improvement of the power conversion efficiency (PCE) and long-term stability of perovskite solar cells. To address this problem, herein, we introduce a fluorine-substituted small molecular material 2FBTA-1 as a bifunctional buffer layer to efficiently passivate the surface defects of perovskite and tune the energy level alignment between the perovskite/2,2',7,7'-tetrakis(N,N-di-(p-methoxyphenyl)amino)-9,9'-spirobifluorene (Spiro-OMeTAD) interface. X-ray photoelectron spectroscopy shows that with the insertion of 2FBTA-1 between perovskite and Spiro-OMeTAD, the metallic Pb0 defects and uncoordinated Pb2+ defects are well restricted. Consequently, the average PCE is distinctly improved from 18.4 ± 0.51 to 20.3 ± 0.40%. Moreover, the long-term stability of unencapsulated devices with 2FBTA-1 treatment under ambient conditions (relative humidity 40-60%) is effectively enhanced, retaining 87% of the initial efficiency after storage for 500 h.

Highly Efficient Phenoxazine Core Unit Based Hole Transport Materials for Hysteresis-Free Perovskite Solar Cells.

Two novel simple-constructed and low-cost hole transport materials (HTMs) POZ9 and POZ10, incorporating a phenoxazine (POZ) core unit, were designed and synthesized for application in perovskite solar cells (PSCs). The typically semblable molecular structure of POZ9 and POZ10 cause them to possess similar energy levels. However, their photovoltaic performances are quite different from each other because of the small variations of N-substitution on POZ ring. The PSCs based on POZ10, which contains three N, N-di-4-methoxyphenylamino units, achieved a power conversion efficiency (PCE) of 19.4%, while the PSC adopting POZ9 as HTM obtained a lower PCE of 17.1%. Moreover, the light intensity dependence research showed that POZ10 has a better hole transporting ability and can efficiently resist the charge recombination.

Molecular Engineering of Triphenylamine-Based Non-Fullerene Electron-Transport Materials for Efficient Rigid and Flexible Perovskite Solar Cells.

There has been a growing interest in the design and synthesis of non-fullerene electron transport materials (ETMs) for perovskite solar cells (PSCs), which may overcome the drawbacks of traditional fullerene derivatives. In this work, a novel donor-acceptor (D-A) structured ETM termed TPA-3CN is presented by molecular engineering of triphenylamine (TPA) as the donor group and (3-cyano-4,5,5-trimethyl-2(5 H)-furanylidene) malononitrile as the acceptor group. To further improve the electron mobility and conductivity and achieve excellent photovoltaic performance, a solution processable n-type dopant is introduced during the ETM spin-coating step. After device optimization, PSCs based on the doped TPA-3CN exhibit an impressive power conversion efficiency (PCE) of 19.2% with a negligible hysteresis. Benefitting from the low temperature and good solution processability of ETM TPA-3CN, it was further applied in flexible inverted PSCs and an impressive PCE of 13.2% was achieved, which is among the highest values reported for inverted flexible fullerene-free PSCs.

[Chinese Holstein Cattle effective population size estimated from whole genome linkage disequilibrium].

Effective populations size (Ne) is an important population parameter that helps to explain genetic variation, population evolution and understanding of the genetic architecture underlying complex traits. With the availability of high-dense SNP panels, more and more researches focus on estimating of Ne using linkage disequilibrium (LD) between SNPs. In this study, we estimated the effective population size from 2093 Chinese Holstein Cattle genotyped with Illumina BovineSNP50 BeadChip. After removal of individual with call rate lt; 95%, SNPs with call rate lt; 95%, minor allele frequency lt; 5% and Hardy-Weinberg Equilibrium test with Plt;0.0001, 1 968 individuals with 38 796 SNPs were remained. Eight kinds of SNP pairs with the distances 0.1, 0.2, 0.5, 1, 2, 5, 10, and 15 Mb were respectively chosen to estimate the effective population size of Chinese Holstein cattle from 4 generations ago. It is demonstrated from the results of this study that the effective population size of Chinese Holstein is decreased in the past generations, and the corresponding effective population size at ~4 generations ago is only around 45.