The Role of Bulk and Interface Recombination in High‐Efficiency Low‐Dimensional Perovskite Solar Cells

2D Ruddlesden–Popper perovskite (RPP) solar cells have excellent environmental stability. However, the power conversion efficiency (PCE) of RPP cells remains inferior to 3D perovskite-based cells. Herein, 2D (CH(CH)NH)(CHNH)PbI perovskite cells with different numbers of [PbI] sheets (n = 2–4) are analyzed. Photoluminescence quantum yield (PLQY) measurements show that nonradiative open-circuit voltage (V) losses outweigh radiative losses in materials with n > 2. The n = 3 and n = 4 films exhibit a higher PLQY than the standard 3D methylammonium lead iodide perovskite although this is accompanied by increased interfacial recombination at the top perovskite/C interface. This tradeoff results in a similar PLQY in all devices, including the n = 2 system where the perovskite bulk dominates the recombination properties of the cell. In most cases the quasi-Fermi level splitting matches the device V within 20 meV, which indicates minimal recombination losses at the metal contacts. The results show that poor charge transport rather than exciton dissociation is the primary reason for the reduction in fill factor of the RPP devices. Optimized n = 4 RPP solar cells had PCEs of 13% with significant potential for further improvements

A tale of two TUTases

The insertion and deletion of U residues at specific sites in mRNAs in trypanosome mitochondria is thought to involve 3′ terminal uridylyl transferase (TUTase) activity. TUTase activity is also required to create the nonencoded 3′ oligo[U] tails of the transacting guide RNAs (gRNAs). We have described two TUTases, RET1 (RNA editing TUTase 1) and RET2 (RNA editing TUTase 2) as components of different editing complexes. Tandem affinity purification-tagged Trypanosoma brucei RET2 (TbRET2) was expressed and localized to the cytosol in Leishmania tarentolae cells by removing the mitochondrial signal sequence. Double-affinity isolation yielded tagged TbRET2, together with a few additional proteins. This material exhibits a U-specific transferase activity in which a single U is added to the 3′ end of a single-stranded RNA, thereby confirming that RET2 is a 3′ TUTase. We also found that RNA interference of RET2 expression in T. brucei inhibits in vitro U-insertion editing and has no effect on the length of the 3′ oligo[U] tails of the gRNAs, whereas down-regulation of RET1 has a minor effect on in vitro U-insertion editing, but produces a decrease in the average length of the oligo[U] tails. This finding suggests that RET2 is responsible for U-insertions at editing sites and RET1 is involved in gRNA 3′ end maturation, which is essential for creating functional gRNAs. From these results we have functionally relabeled the previously described TUT-II complex containing RET1 as the guide RNA processing complex

Tailored Local Bandgap Modulation as a Strategy to Maximize Luminescence Yields in Mixed‐Halide Perovskites

Funder: Winton Programme for the Physics of SustainabilityFunder: EPSRC Doctoral Prize FellowshipFunder: Bavarian research network SolTechFunder: Studienstiftung des deutschen VolkesFunder: DFG Emmy Noether ProgramAbstract: Halide perovskites have emerged as high‐performance semiconductors for efficient optoelectronic devices, not least because of their bandgap tunability using mixtures of different halide ions. Here, temperature‐dependent photoluminescence microscopy with computational modelling is combined to quantify the impact of local bandgap variations from disordered halide distributions on the global photoluminescence yield in mixed‐halide perovskite films. It is found that fabrication temperature, surface energy, and charge recombination constants are keys for describing local bandgap variations and charge carrier funneling processes that control the photoluminescence quantum efficiency. It is reported that further luminescence efficiency gains are possible through tailored bandgap modulation, even for materials that have already demonstrated high luminescence yields. The work provides a novel strategy and fabrication guidelines for further improvement of halide perovskite performance in light‐emitting and photovoltaic applications

Effect of indentation load and time on knoop and vickers microhardness tests for enamel and dentin

The aim of this study was to determine the effect of variations in indentation load and time on the Knoop and Vickers hardness numbers (KHN and VHN) for enamel and dentin. Twenty molar teeth were divided into twenty enamel and twenty dentin specimens. Each specimen was tested using a Knoop or Vickers microhardness tester at different loads and times. The difference in hardness between the groups was analyzed with two-way ANOVA followed by a Tukey test. The results revealed that a difference of indentation time did not influence the microhardness number of enamel and dentin. The KHN values of enamel and the VHN values of dentin were affected by variation of test loads. Therefore, the tooth hardness number for different loads may not be acceptable for comparison