Low Density of Conduction and Valence Band States Contribute to the High Open-Circuit Voltage in Perovskite Solar Cells

Hybrid perovskites are widely used for high-performance solar cells. Large diffusion lengths and long charge carrier lifetimes are considered two main factors for their high performance. Here, we argue that not only large diffusion lengths and long carrier lifetimes but also the low densities of the conduction and valence band states (<i>N</i>_c, <i>N</i>_v) contribute to high-performance perovskite solar cells. We estimated <i>N</i>_c and <i>N</i>_v of silicon, CdTe, and typical perovskites with two different methods. It was found that <i>N</i>_c and <i>N</i>_v of perovskites and CdTe are much lower than that of silicon. Using numerical models, we found that the solar cell of a material with same characteristics but lower <i>N</i>_c and <i>N</i>_v can realize a higher open-circuit voltage (<i>V</i>_oc) and higher power conversion efficiency (PCE). We put forward and proved that the low <i>N</i>_c and <i>N</i>_v in hybrid perovskite is one of the factors for its high performance. This provides a new guideline for finding and developing new photovoltaic candidate materials

Solvent Accommodation: Functionalities Can Be Tailored Through Co-Crystallization Based on 1:1 Coronene‑F₄TCNQ Charge-Transfer Complex

Because organic donor/acceptor blending systems play critical roles in ambipolar transistors, photovoltaics, and light-emitting transistors, it is highly desirable to precisely tailor the stacking of cocrystals toward different intrinsic structures and physical properties. Here, we demonstrated that the structure-stacking modes and electron-transport behaviors of coronene-F4TCNQ cocrystals (1:1) can be tuned through the solvent accommodation. Our results clearly show that the solvent accommodation not only enlarges the inner mixed packing (...DAD···) distances, leading to the depressed short-contact interactions including the side-by-side and face-by-face intermolecular interactions, but also switches off electron-transport behavior of coronene-F₄TCNQ cocrystals (1:1) in ambient atmosphere

Polyaniline-Grafted Graphene Hybrid with Amide Groups and Its Use in Supercapacitors

Unlike conventional routes for preparing graphene/polyaniline (G/PANI) composites coupled by van der Waals forces, an approach to graft polyaniline (PANI) nanofibers onto graphene to acquire a polyaniline–graphene (PANI–G) hybrid connected by amide groups is described in this study. The chemical bonding between graphene and PANI is confirmed by infrared spectroscopy and X-ray photoelectron spectroscopy. The Raman spectrum of PANI–G hybrid demonstrates a close interaction between graphene and PANI. Electrochemical tests show that PANI–G hybrid has a high capacitance (623.1 F/g) at a current density of 0.3 A/g, higher than that in G/PANI composites reported previously. In addition, the retained capacitance of the PANI–G hybrid in the long term charge/discharge cycling test reached as high as 510 F/g at a current density of 50 A/g, suggesting its potential use in supercapacitors. First-principle calculations were carried out to study the electronic structures of PANI–G hybrid. The results show that the carbonyl group in the amide linkage plays a key role in the formation of π-conjugated structure, facilitates charge transfer, and consequently improves capacitance and cycling ability

Polymer-Assisted Single Crystal Engineering of Organic Semiconductors To Alter Electron Transport

A new crystal phase of a naphthalenediimide derivative (α-DPNDI) has been prepared via a facial polymer-assisted method. The stacking pattern of DPNDI can be tailored from the known one-dimensional (1D) ribbon (β phase) to a novel two-dimensional (2D) plate (α phase) through the assistance from polymers. We believe that the presence of polymers during crystal growth is likely to weaken the direct π–π interactions and favor side-to-side C–H−π contacts. Furthermore, β phase architecture shows electron mobility higher than that of the α phase in the single-crystal-based OFET. Theoretical calculations not only confirm that β-DPNDI has an electron transport performance better than that of the α phase but also indicate that the α phase crystal displays 2D transport while the β phase possesses 1D transport. Our results clearly suggest that polymer-assisted crystal engineering should be a promising approach to alter the electronic properties of organic semiconductors

Polymer-Assisted Single Crystal Engineering of Organic Semiconductors To Alter Electron Transport

A new crystal phase of a naphthalenediimide derivative (α-DPNDI) has been prepared via a facial polymer-assisted method. The stacking pattern of DPNDI can be tailored from the known one-dimensional (1D) ribbon (β phase) to a novel two-dimensional (2D) plate (α phase) through the assistance from polymers. We believe that the presence of polymers during crystal growth is likely to weaken the direct π–π interactions and favor side-to-side C–H−π contacts. Furthermore, β phase architecture shows electron mobility higher than that of the α phase in the single-crystal-based OFET. Theoretical calculations not only confirm that β-DPNDI has an electron transport performance better than that of the α phase but also indicate that the α phase crystal displays 2D transport while the β phase possesses 1D transport. Our results clearly suggest that polymer-assisted crystal engineering should be a promising approach to alter the electronic properties of organic semiconductors