An intrinsic electrical conductivity study of perovskite powders MAPbX3 (X = I, Br, Cl) to investigate its effect on their photovoltaic performance.

An investigation into the intrinsic electrical conductivity of perovskite powders MAPbX3, where X represents iodine (I), bromine (Br), or chlorine (Cl), was conducted to explore its impact on their photovoltaic performance. Results revealed that MAPbCl3 demonstrated light absorption ability in the ultraviolet and visible regions, while MAPbBr3 showed capacity for light absorption at longer wavelengths in the visible spectrum. On the other hand, MAPbI3 exhibited good absorption at longer wavelengths, indicating its ability to absorb light in the near-infrared region. The optical bandgap of each perovskite was determined to be 2.90 eV for MAPbCl3, 2.20 eV for MAPbBr3, and 1.47 eV for MAPbI3. The electrical conductivities of these powders were measured in-plane using the four-probe method and through-plane by electrochemical impedance spectroscopy (EIS). Electrochemical impedance spectroscopy (EIS) studies revealed a significant change in the conductivity of the MAPbI3 perovskite at temperatures between 80 °C and 100 °C. This change could be attributed to structural modifications induced when the temperature exceeds these values. The through-plane conductivity changed from 3 × 10-8 S cm-1 at 60 °C to approximately 6 × 10-5 S cm-1 at 120 °C and around 2 × 10-3 S cm-1 at 200 °C. Meanwhile, the sheet conductivity (in-plane conductivity) measurements performed at ambient temperature reveal that sheet conductivities are 489 × 103 S m-1, 486 × 103 S m-1 and 510 × 103 S m-1 for MAPbBr3, MAPbCl3 and MAPbI3, respectively. This study provides valuable insights for optimizing the performance of perovskite solar cells. Understanding how dopants influence the electrical conductivity and photovoltaic properties of the perovskite material, this work will enable researchers to design and engineer more efficient and stable solar cell devices based on MAPbX3 perovskites.

Harnessing prion-inspired amyloid self-assembly for sustainable and biocompatible proton conductivity.

Protein-based materials have emerged as promising candidates for proton-conducting biomaterials. Therefore, drawing inspiration from the amino acid composition of prion-like domains, we designed short self-assembling peptides incorporating the (X-Tyr) motif, with X representing Asn, Gly and Ser, which form fibrillar structures capable of conducting protons. In this study, we conducted an analysis of the conductivity capacity of these fibers, with a focus on temperature and frequency dependence of conductivity. The loss tangent curves data and the electrode polarization model with the Debye approximation were employed to calculate transport properties, including conductivity, diffusivity, and density of charge carriers. Results revealed the prion-like fibers can transport protons more efficiently than biomaterials and other synthetic proton conducting materials, and that a significant increase in conductivity is observed with fibrillar orientations. The temperature dependence of conductivity of the peptides, measured in wet conditions, showed conductivities following the trend σ(NY7) < σ(GY7) < σ(SY7), in all the range of temperatures studied. The Arrhenius behavior, and the activation energy associated with conductivity followed the trend: Eact (SY7) = 8.2 ± 0.6 kJ mol-1 < Eact (GY7) < 13 ± 5 kJ mol-1 < Eact (NY7) = 31 ± 7 kJ mol-1, in different range of temperatures depending of the peptide. Furthermore, the diffusion coefficient correlated with increasing temperature in GY7 and SY7 fibers for temperatures compress between 20 °C and 80 °C, while NY7 only below 60 °C. However, it is noteworthy that the diffusivity observed in the SY7 peptide is lower, compared to GY7 and NY7 presumably due to its enlarged length. This observation can be attributed to two factors: firstly, the higher conductivity values observed in SY7 compared to GY7 and NY7, and secondly, to the value of relation observed of cations present in the peptide SY7 compared with GY7 and NY7, which in turn is dependent on temperature. In light of these findings, we envision our prion-inspired nanofibers as highly efficient proton-conducting natural biopolymers that are both biocompatible and biodegradable. These properties provide the opportunity for the development of next-generation bioelectrical interfaces and protonic devices.

Polylactic Acid Nanofiber Membranes Grafted with Carbon Nanotubes with Enhanced Mechanical and Electrical Properties.

Electroconductive materials based on poly(lactic acid) (PLA) electrospinning membranes grafted with carbon nanotubes (CNTs) functionalized with the carboxylic group R-COOH have been obtained. PLA electrospun membranes were modified with sulfuric acid (H2SO4) to oxidize its surface to subsequently graft the CNTs, the treatment time and drying of the membranes before grafting with CNTs being critical, influencing the final properties of the materials. SEM images showed that CNTs presented a uniform distribution on the surface of the PLA nanofibers, while FTIR spectra of PLA-CNTs materials revealed characteristic hydroxyl groups, as evidenced by absorption peaks of CNTs. Thanks to the grafting with CNTs, the resulting PLA-CNTs membranes present an improvement of the mechanical and conductive properties when compared with PLA membranes. On the one hand, grafting with CNTs causes the nanofibers to have greater rigidity, so they are more manipulable and can more easily preserve their conformation when stress is exerted. On the other hand, grafting with CNTs allows elimination of the insulating barrier of the PLA, reducing the resistivity and providing high electrical conductivity to the PLA-CNTs membranes. The incorporation of CNTs into PLA electrospun membranes is expected to offer greater functionalities to electrospun composite nanofibers for medical and industrial applications.