A new class of polymeric hole-transport materials (HTMs) are explored by inserting a two-dimensionally conjugated fluoro-substituted pyrene into thiophene and selenophene polymeric chains. The broad conjugated plane of pyrene and “Lewis soft” selenium atoms not only enhance the π–π stacking of HTM molecules greatly but also render a strong interaction with the perovskite surface, leading to an efficient charge transport/transfer in both the HTM layer and the perovskite/HTM interface. Note that fluorine substitution adjacent to pyrene boosts the stacking of HTMs towards a more favorable face-on orientation, further facilitating the efficient charge transport. As a result, perovskite solar cells (PSCs) employing PE10 as dopant-free HTM afford an excellent efficiency of 22.3 % and the dramatically enhanced device longevity, qualifying it among the best PSCs based on dopant-free HTMs. 

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 pi-pi 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.

Materials design of efficient electrochemical micro-reactors is challenging, although hierarchically structured, self-standing electrodes with catalyst arrays offer promise. Herein, catalyst function in compact micro-reactor electrodes is designed by nanostructural tailoring of carbonized wood for efficient water splitting. Specifically, NiFe rod tipped, N-doped graphitic carbon nanocapsule arrays are self-assembled in hierarchical wood, and the benefit of this unique presentation and its promotive effect on accessibility of the catalyst surfaces is apparent. This report also comprises the first wood based micro-reactor electrodes for electrocatalytic water oxidation demonstrating excellent performance. The overpotential for oxygen evolution reaction was as low as 180 mV for 10 mA cm−2 current density and TOFredox was high at a level of 5.8 s−1 (at 370 mV overpotential). This hierarchical electrode can also work as bifunctional catalyst (both as anodic and as cathodic electrode) for total water splitting with a cell potential of 1.49 V for 10 mA cm−2 in alkaline solution, suggestive of their potential also in other electrochemical applications.

Ammonia production consumes ~2% of the annual worldwide energy supply, therefore strategic alternatives for the energy-intensive ammonia synthesis through the Haber-Bosch process are of great importance to reduce our carbon footprint. Inspired by MoFe-nitrogenase and the energy-efficient and industrially feasible electrocatalytic synthesis of ammonia, we herein establish a catalytic electrode for artificial nitrogen fixation, featuring a carbon fiber cloth fully grafted by boron-doped molybdenum disulfide (B-MoS2/CFC) nanosheets. An excellent ammonia production rate of 44.09 μg h–1 cm–2 is obtained at −0.2 V versus the reversible hydrogen electrode (RHE), whilst maintaining one of the best reported Faradaic efficiency (FE) of 21.72% in acidic aqueous electrolyte (0.1 M HCl). Further applying a more negative potential of −0.25 V renders the best ammonia production rate of 50.51 μg h–1 cm–2. A strong-weak electron polarization (SWEP) pair from the different electron accepting and back-donating capacities of boron and molybdenum (2p shell for boron and 5d shell for molybdenum) is proposed to facilitate greatly the adsorption of non-polar dinitrogen gas via N≡N bond polarization and the first protonation with large driving force. In addition, for the first time a visible light driven photo-electrochemical (PEC) cell for overall production of ammonia, hydrogen and oxygen from water + nitrogen, is demonstrated by coupling a bismuth vanadate BiVO4 photo-anode with the B-MoS2/CFC catalytic cathode.

Fused-ring electron acceptor (FREA) based ternary organic solar cells (OSCs) have made significant progress and attracted considerable attention due to their simple device architecture and broad absorption range in devices. There are three key parameters that need to be fine-tuned in ternary OSCs including absorption, energy level and morphology in order to realize high efficiencies. Herein, a series of FREAs with diverse electron-rich cores or electron-deficient terminals are developed and rationally combined to achieve high performance ternary OSCs. The dipole moment of FREAs' terminals has been unveiled as an important factor and its working mechanism has been thoroughly investigated by systematically studying six ternary OSCs. These ternary blends all exhibit complementary absorption and cascade energy levels, which can facilitate efficient light-harvesting and charge transfer. Additionally, the morphological effects on ternary OSCs are eliminated through comparative studies while demonstrating distinctively different performance. The preliminary results show that compatible dipole moment between two FREAs is critical in ternary blends. Specifically, the performance of the ternary system with two FREAs having quite different dipole moment terminals is worse compared to that with similar terminal dipole moments. The pair with larger difference in the dipole moment will also negatively impact device performance. This interesting phenomenon is likely due to the fact that very different dipole moments of terminals in FREAs can significantly decrease the electron mobility as well as induce unbalanced hole/electron transport. Consequently, it results in increased charge recombination and reduced charge collection efficiency. This finding demonstrates that the dipole moment of FREAs should be taken into account in designing ternary OSCs.

A facile preparation of bio-inspired and morphology controllable catalytic electrode FeS@MoS2/CFC, featuring a carbon fiber cloth (CFC) covered with FeS dotted MoS2 nanosheets, has been established. Synergy between the CFC as a self-standing conductive substrate and the FeS nanoparticle dotted MoS2 nanosheets with abundant active sites makes the noble-metal-free catalytic electrode FeS@MoS2/CFC highly efficient in nitrogen reduction reaction (NRR), with an ammonia production rate of 8.45 mu g h(-1) cm(-2) and excellent long-term stability at -0.5 V in pH neutral electrolyte. Further electrolysis in acidic and alkaline electrolytes revealed the overall NRR catalytic activity of this electrode over a wide pH range.

Four weak donor backbones (BT, BTP, BT2, and BT3), featuring stepwise enhanced electron-donating capacities, are designed and synthesized. The sp(3) type carbons introduced are tethered with auxiliary groups to generate a better electron-blocking stereoscopic structure. A series of NB dyes are subsequently synthesized from these central cores by end-capping a strong diphenylamine donor and a planar heterocyclic acceptor 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic acid. The fine-tuning of steric configurations and energy levels of the resulting dye molecules reduces the energy losses significantly when applied in dye-sensitized solar cells. These devices offer one of the highest open-circuit voltages (approximate to 1.03 V) reported so far, and high power conversion efficiencies of 9.6%-12.1% using the NB dyes in combination with a well-developed cobalt-tris(4-methoxyphenyl)amine-based tandem electrolyte.

Organic thin-film solar cells have demonstrated a bright prospect for commercial applications, where organic photosensitizers act as the most important kernel. In the global motif of sustainable development, unrelenting research efforts have been devoted to the exploration of organic material containing photosensitizers to achieve low-cost conversion of solar energy to clean electricity. In this work, two star-shaped donor cores, T1 and T2, which consist of fused thiophene triazatruxene, have been synthesized and applied in two different types of solar cells. The two-dimensional pi-bonded extension enhances their electron-donating capability and induces relatively strong intermolecular pi-pi stacking. The C-3h symmetrical donor isomers, featuring planar backbones and three-dimensional structures, are found to contribute toward a promising prospect for overall photoelectric applications.

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 dopant-free 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.