Recent progress in developing efficient monolithic all-perovskite tandem solar cells

Organic–inorganic halide perovskites have received widespread attention thanks to their strong light absorption,long carrier diffusion lengths,tunable bandgaps,and low temperature processing.Single-junction perovskite solar cells(PSCs)have achieved a boost of the power conversion efficiency(PCE)from 3.8%to 25.2%in just a decade.With the continuous growth of PCE in single-junction PSCs,exploiting of monolithic all-perovskite tandem solar cells is now an important strategy to go beyond the efficiency available in single-junction PSCs.In this review,we first introduce the structure and operation mechanism of monolithic all-perovskite tandem solar cell.We then summarize recent progress in monolithic all-perovskite tandem solar cells from the perspectives of different structural units in the device:tunnel recombination junction,wide-bandgap top subcell,and narrow-bandgap bottom subcell.Finally,we provide our insights into the challenges and scientific issues remaining in this rapidly developing research field.

Comparative genome analysis of three euplotid protists provides insights into the evolution of nanochromosomes in unicellular eukaryotic organisms

One of the most diverse clades of ciliated protozoa,the class Spirotrichea,displays a series of unique characters in terms of eukaryotic macronuclear(MAC)genome,including high fragmentation that produces nanochromosomes.However,the genomic diversity and evolution of nanochromosomes and gene families for spirotrich MAC genomes are poorly understood.In this study,we assemble the MAC genome of a representative euplotid(a new model organism in Spirotrichea)species,Euplotes aediculatus.Our results indicate that:(a)the MAC genome includes 35,465 contigs with a total length of 97.3 Mb and a contig N50 of 3.4 kb,and contains 13,145 complete nanochromosomes and 43,194 predicted genes,with the majority of these nanochromosomes containing tiny introns and harboring only one gene;(b)genomic comparisons between E.aediculatus and other reported spirotrichs indicate that average GC content and genome fragmentation levels exhibit interspecifc variation,and chromosome breaking sites(CBSs)might be lost during evolution,resulting in the increase of multi-gene nanochromosome;(c)gene families associated with chitin metabolism and FoxO signaling pathway are expanded in E.aediculatus,suggesting their potential roles in environment adaptation and survival strategies of E.aediculatus;and(d)a programmed ribosomal frameshift(PRF)with a conservative motif 5′-AAATAR-3′tends to occur in longer genes with more exons,and PRF genes play an important role in many cellular regulation processes.

Monitoring and evaluation of disaster risk caused by linkage failure and instability of residual coal pillar and rock strata in multi-coal seam mining

Comprehensive research methods such as literature research,theoretical analysis,numerical simulations and field monitoring have been used to analyze the disasters and characteristics caused by the linkage failure and instability of the residual coal pillars-rock strata in multi-seam mining.The effective monitoring area and monitoring design method of linkage instability of residual coal pillar-rock strata in multi-seam mining have been identified.The evaluation index and the risk assessment method of disaster risk have been established and the project cases have been applied and validated.The results show that:①The coal pillar will not only cause disaster in singleseam mining,but also more easily cause disaster in multi-seam mining.The instability of coal pillars can cause not only dynamical disasters such as rock falls and mine earthquakes,but also cause surface subsidence and other disasters.②When monitoring the linkage instability of residual coal pillar-rock strata,it is not only necessary to consider the monitoring of the apply load body(key block),the transition body(residual coal pillar)and the carrier body(interlayer rock and working face),but also to strengthen the monitoring of the fracture development height(linkage body).③According to the principles of objectivity,easy access and quantification,combined with investigation,analysis,and production and geological characteristics of this mining area,the main evaluation indexes of the degree of disaster caused by linkage instability of residual coal pillar-rock strata are determined as:microseismic energy,residual coal pillar damage degree,fracture development height.And the evaluation index classification table was also given.④According to the measured value of the evaluation index,the fuzzy comprehensive evaluation method was used to calculate the disaster risk degree in the studied mine belongs to class III,that is,medium risk level.The corresponding pressure relief technology was adopted on site,which achieved a good control effect,and also verified the accuracy and effectiveness of the risk evaluation results.

Further analyses of variation of ribosome DNA copy number and polymorphism in ciliates provide insights relevant to studies of both molecular ecology and phylogeny

Sequence-based approaches, such as analyses of ribosome DNA(rDNA) clone libraries and high-throughput amplicon sequencing, have been used extensively to infer evolutionary relationships and elucidate the biodiversity in microbial communities.However, recent studies demonstrate both r DNA copy number variation and intra-individual(intra-genomic) sequence variation in many organisms, which challenges the application of the rDNA-based surveys. In ciliates, an ecologically important clade of microbial eukaryotes, rDNA copy number and sequence variation are rarely studied. In the present study, we estimate the intraindividual small subunit rDNA(SSU r DNA) copy number and sequence variation in a wide range of taxa covering nine classes and 18 orders of the phylum Ciliophora. Our studies reveal that:(i) intra-individual sequence variation of SSU rDNA is ubiquitous in all groups of ciliates detected and the polymorphic level varies among taxa;(ii) there is a most common version of SSU rDNA sequence in each cell that is highly predominant and may represent the germline micronuclear template;(iii)compared with the most common version, other variant sequences differ in only 1–3 nucleotides, likely generated during macronuclear(somatic) amplification;(iv) the intra-cell sequence variation is unlikely to impact phylogenetic analyses;(v) the rDNA copy number in ciliates is highly variable, ranging from 103 to 106, with the highest record in Stentor roeselii. Overall,these analyses indicate the need for careful consideration of SSU r DNAvariation in analyses of the role of ciliates in ecosystems.

Enzymatic and chemical mapping of nucleosome distribution in purified micro- and macronuclei of the ciliated model organism, Tetrahymenathermophila

Genomic distribution of the nucleosome, the basic unit of chromatin, contains important epigenetic information. To map nucleosome distribution in structurally and functionally differentiated micronucleus(MIC) and macronucleus(MAC) of the ciliate Tetrahymena thermophila, we have purified MIC and MAC and performed micrococcal nuclease(MNase) digestion as well as hydroxyl radical cleavage. Different factors that may affect MNase digestion were examined, to optimize mono-nucleosome production. Mono-nucleosome purity was further improved by ultracentrifugation in a sucrose gradient. As MNase concentration increased, nucleosomal DNA sizes in MIC and MAC converged on 147 bp, as expected for the nucleosome core particle. Both MNase digestion and hydroxyl radical cleavage consistently showed a nucleosome repeat length of^200 bp in MAC of Tetrahymena, supporting ~50 bp of linker DNA. Our work has systematically tested methods currently available for mapping nucleosome distribution in Tetrahymena, and provided a solid foundation for future epigenetic studies in this ciliated model organism.

Histone methyltransferase TXRl is required for both H3 and H3.3lysine 27 methylation in the well-known ciliated protist Tetrahymena thermophila

DNA replication elongation is tightly controlled by histone-modifying enzymes.Our previous studies showed that the histone methytransferase TXRl(Tetrahymena Trithorax related protein 1) specifically catalyzes H3K27 monomethylation and affects DNA replication elongation in Tetrahymena thermophila.In this study,we investigated whether TXRl has a substrate preference to the canonical H3 over the replacement variant H3.3.We demonstrated by histone mutagenesis that K27 Q mutation in H3.3further aggravated the replication stress phenotype of K27 Q mutation in canonical H3,supporting H3.3 as a physiologically relevant substrate of TXRl.This result is in apparent contrast to the strong preference for canonical H3 recently reported in Arabidopsis homologues ATXR5 and ATXR6,and further corroborates the role of TXRl in DNA replication.

Cross-linked hole transport layers for high-efficiency perovskite tandem solar cells

Perovskite tandem solar cells have recently received extensive attention due to their promise of achieving power conversion efficiency(PCE)beyond the limits of single-junction cells.However,their performance is still largely constrained by the widebandgap perovskite solar cells which show considerable open-circuit voltage(VOC)losses.Here,we increase the VOCand PCE of wide-bandgap perovskite solar cells by changing the hole transport layer(HTL)from commonly used poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)(PTAA)to in-situ cross-linked small molecule N_(4),N_(4)′-di(naphthalen-1-yl)-N_(4),N_(4)′-bis(4-vinylphenyl)biphenyl-4,4′-diamine(VNPB).The stronger interaction and lower trap density at the VNPB/perovskite interface improve the PCE and stability of wide-bandgap perovskite solar cells.By using the cross-linked HTL for front wide-bandgap subcells,PCEs of 24.9%and 25.4%have been achieved in perovskite/perovskite and perovskite/silicon tandem solar cells,respectively.The results demonstrate that cross-linkable small molecules are promising for high-efficiency and cost-effective perovskite tandem photovoltaic devices.

Revealing the output power potential of bifacial monolithic all-perovskite tandem solar cells

Bifacial monolithic all-perovskite tandem solar cells have the promise of delivering higher output power density by inheriting the advantages of both tandem and bifacial architectures simultaneously.Herein,we demonstrate,for the first time,the bifacial monolithic all-perovskite tandem solar cells and reveal their output power potential.The bifacial tandems are realized by replacing the rear metal electrodes of monofacial tandems with transparent conduction oxide electrodes.Bandgap engineering is deployed to achieve current matching under various rear illumination conditions.The bifacial tandems show a high output power density of 28.51 mW cm−2 under a realistic rear illumination(30 mW cm−2).Further energy yield calculation shows substantial energy yield gain for bifacial tandems compared with the monofacial tandems under various ground albedo for different climatic conditions.This work provides a new device architecture for higher output power for all-perovskite tandem solar cells under real-world conditions.