Perovskite solar cells (PSCs) has skyrocketed in the past decade to an unprecedented level due to their outstanding photoelectric properties and facile processability. However, the utilization of expensive hole transport materials (HTMs) and the inevitable instability instigated by the deliquescent dopants represent major concerns hindering further commercialization. Here, a series of low-cost, conjugated polymers are designed and applied as dopantfree HTMs in PSCs, featuring tuned energy levels, good temperature and humidity resistivity, and excellent photoelectric properties. Further studies highlight the critical and multifaceted roles of the polymers with respect to facilitating charge separation, passivating the surface trap sites of perovskite materials, and guaranteeing long-term stability of the devices. A stabilized power conversion efficiency (PCE) of 20.3% and remarkably enhanced device longevity are achieved using the dopant-free polymer P3 with a low concentration of 5 mg/mL, qualifying the device as one of the best PSC systems constructed on the basis of dopant-free HTMs so far. In addition, the flexible PSCs based on P3 also exhibit a PCE of 16.2%. This work demonstrates a promising route toward commercially viable, stable, and efficient PSCs.

A three‐tiered cake‐style composite is elaborately established, with the characteristic of a double‐deck of MoS2 nanosheets and reduction of graphene oxide (RGO) sheets dotted with CoS2 nanoparticles (CoS2@MoS2/RGO). Because of the prominent synergistic effect of graphene acting as conductive support, MoS2 and CoS2 providing abundant catalytically active sites, and the cake‐style structure promoting mechanical stability, the CoS2@MoS2/RGO exhibits a superior hydrogen evolution reaction activity with a small overpotential of 98 mV at cathodic current density of 10 mA cm−2, and a small Tafel slope of 37.4 mV dec−1, as well as excellent cycling stability. Density functional theory calculations reveal that the hydrogen adsorption free energy of CoS2@MoS2/RGO is close to zero.

Conjugated polymers are regarded as promising candidates for dopant-free hole-transport materials (HTMs) in efficient and stable perovskite solar cells (PSCs). Thus far, the vast majority of polymeric HTMs feature structurally complicated benzo­[1,2-b:4,5-b’]­dithiophene (BDT) analogs and electron-withdrawing heterocycles, forming a strong donor–acceptor (D–A) structure. Herein, a new class of phenanthrocarbazole (PC)-based polymeric HTMs (PC1, PC2, and PC3) has been synthesized by inserting a PC unit into a polymeric thiophene or selenophene chain with the aim of enhancing the π–π stacking of adjacent polymer chains and also to efficiently interact with the perovskite surface through the broad and planar conjugated backbone of the PC. Suitable energy levels, excellent thermostability, and humidity resistivity together with remarkable photoelectric properties are obtained via meticulously tuning the conformation and elemental composition of the polymers. As a result, PSCs containing PC3 as dopant-free HTM show a stabilized power conversion efficiency (PCE) of 20.8% and significantly enhanced longevity, rendering one of the best types of PSCs based on dopant-free HTMs. Subsequent experimental and theoretical studies reveal that the planar conformation of the polymers contributes to an ordered and face-on stacking of the polymer chains. Furthermore, introduction of the “Lewis soft” selenium atom can passivate surface trap sites of perovskite films by Pb–Se interaction and facilitate the interfacial charge separation significantly. This work reveals the guiding principles for rational design of dopant-free polymeric HTMs and also inspires rational exploration of small molecular HTMs.

Inhibiting excessive aggregation and migration of active layer molecules is essential to improve the stability and performance of organic solar cells (OSCs). Herein, the star-shaped nitrogen heterocyclic-ring acceptor TF1 featuring...

As the advanced catalysts for hydrogen evolution reaction (HER), MoS2-based electrocatalysts have attracted tremendous efforts in order to enhance the HER activity. Herein, a facile method is reported to prepare the new type of defect-and Srich ultrathin MoS2 nanosheets embedded in N-doped carbon nanofibers composites (MoS2/NCNFs), which demonstrates a small HER overpotential of 135 mV at 10 mA cm −2 and a large cathodic current density of 65.6 mA cm −2 at only 200 mV. Futhermore, a small Tafel slope of 48 mV dec −1 , a large exchange current density of 24.2 μA cm −2 , as well as superior cycling stability are obtained. This success of embedding defect-and S-rich ultrathin MoS2 nanosheets in N-doped carbon nanofibers paves a new avenue for highly efficient catalysts for HER in the near future.

No abstract

The CoS2/CoSe2 hybrid catalyst exhibits superior HER electrocatalytic activity as well as excellent electrochemical durability. CoSe2/DETA nanobelts not only afford an interconnected conducting network, but also demonstrate superior HER electrocatalytic activity. High dispersion and smaller CoS2 nanoparticles on the surface can provide abundant active sites for the HER.

In this work, we synthesized a novel hybrid catalyst (CoB/CoSe) by growing amorphous CoB on the surface of CoSe nanosheets. Benefiting from the prominent coupled effects between CoB and CoSe nanosheets, an efficient oxygen evolution reaction catalyst CoB/CoSe exhibits a very low overpotential of 320 mV @ 10 mA cm with a Tafel slope of 56.0 mV dec in alkaline medium. An overpotential of 300 mV can also be achieved by CoB/CoSe at the same condition for hydrogen evolution reaction. Notably, at the applied potential of 1.73 V, the electrocatalyst CoB/CoSe demonstrates a current density of 10 mA cm for overall water splitting and displays an outstanding long-term stability. The faradaic efficiencies of CoB/CoSe for both hydrogen and oxygen evolution are close to 100%.