Two low-cost spiro[fluorene-9,9 0 -xanthene] (SFX)-based 3D organic hole transport materials (HTMs), termed X54 and X55, were tailor-made by a one-pot synthesis approach for perovskite solar cells (PSCs). PSC devices based on X55 as the HTM show a very impressive power-conversion efficiency of 20.8% under 100 mW$cm À2 AM1.5G solar illumination, which is much higher than the PCE of the reference devices based on X54 (13.6%) and the standard HTM-Spiro-OMeTAD (18.8%) under the same conditions. HIGHLIGHTS Two SFX-based 3D oligomers were tailor-made by a one-pot synthesis approachOne of the oligomers, X55, was successfully applied in highly efficient PSCs High efficiency of 20.8% was achieved with X55 as the hole transport material The low-cost 3D HTMs can render a PCE close to 21% in PSCs Xu et al., Chem 2, 676-687 May 11, 2017 ª 2017 Elsevier Inc. http://dx. SUMMARYThe power-conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have increased rapidly from about 4% to 22% during the past few years. One of the major challenges for further improvement of the efficiency of PSCs is the lack of sufficiently good hole transport materials (HTMs) to efficiently scavenge the photogenerated holes and aid the transport of the holes to the counter-electrode in the PSCs. In this study, we tailor-made two low-cost spiro[fluorene-9,9 0xanthene] (SFX)-based 3D oligomers, termed X54 and X55, by using a one-pot synthesis approach for PSCs. One of the HTMs, X55, gives a much deeper HOMO level and a higher hole mobility and conductivity than the state-of-theart HTM, Spiro-OMeTAD. PSC devices based on X55 as the HTM show a very impressive PCE of 20.8% under 100 mW$cm À2 AM1.5G solar illumination, which is much higher than the PCE of the reference devices based on Spiro-OMeTAD (18.8%) and X54 (13.6%) under the same conditions.

Tremendous progress has recently been achieved in the field of perovskite solar cells (PSCs) as evidenced by impressive power conversion efficiencies (PCEs); but the high PCEs of >20% in PSCs has so far been mostly achieved by using the hole transport material (HTM) spiro-OMeTAD; however, the relatively low conductivity and high cost of spiro-OMeTAD significantly limit its potential use in large-scale applications. In this work, two new organic molecules with spiro[fluorene-9,9′-xanthene] (SFX)-based pendant groups, X26 and X36, have been developed as HTMs. Both X26 and X36 present facile syntheses with high yields. It is found that the introduced SFX pendant groups in triphenylaminebased molecules show significant influence on the conductivity, energy levels, and thin-film surface morphology. The use of X26 as HTM in PSCs yields a remarkable PCE of 20.2%. In addition, the X26-based devices show impressive stability maintaining a high PCE of 18.8% after 5 months of aging in controlled (20%) humidity in the dark.

Exploration of efficient water oxidation catalysts (WOCs) is the primary challenge in conversion of renewable energy into fuels. Here we report a molecularly well-defined heterogeneous WOC with Aza-fused, π-conjugated, microporous polymer (Aza-CMP) coordinated single cobalt sites (Aza-CMP-Co). The single cobalt sites in Aza-CMP-Co exhibited superior activity under alkaline and near-neutral conditions. Moreover, the molecular nature of the isolated catalytic sites makes Aza-CMP-Co a reliable model for studying the heterogeneous water oxidation mechanism. By a combination of experimental and theoretical results, a pH-dependent nucleophilic attack pathway for O-O bond formation was proposed. Under alkaline conditions, the intramolecular hydroxyl nucleophilic attack (IHNA) process with which the adjacent -OH group nucleophilically attacks Co4+=O was identified as the rate-determining step. This process leads to lower activation energy and accelerated kinetics than those of the intermolecular water nucleophilic attack (WNA) pathway. This study provides significant insights into the crucial function of electrolyte pH in water oxidation catalysis and enhancement of water oxidation activity by regulation of the IHNA pathway.

Spintronics holds great potential for next-generation high-speed and low–power consumption information technology. Recently, lead halide perovskites (LHPs), which have gained great success in optoelectronics, also show interesting magnetic properties. However, the spin-related properties in LHPs originate from the spin-orbit coupling of Pb, limiting further development of these materials in spintronics. Here, we demonstrate a new generation of halide perovskites, by alloying magnetic elements into optoelectronic double perovskites, which provide rich chemical and structural diversities to host different magnetic elements. In our iron-alloyed double perovskite, Cs2Ag(Bi:Fe)Br6, Fe3+ replaces Bi3+ and forms FeBr6 clusters that homogenously distribute throughout the double perovskite crystals. We observe a strong temperature-dependent magnetic response at temperatures below 30 K, which is tentatively attributed to a weak ferromagnetic or antiferromagnetic response from localized regions. We anticipate that this work will stimulate future efforts in exploring this simple yet efficient approach to develop new spintronic materials based on lead-free double perovskites.

Minimizing the interfacial defects and improving the charge transferability of charge-transfer layers have become the most important strategies to boost the efficiency and stability of perovskite solar cells. However, most molecular passivators currently employed to alleviate interfacial defects generate poorly conductive aggregates at the interfaces, hindering the extraction of charge carriers. Here, a holistic interface engineering strategy employing a highly crystalline small molecule of 2,7-dioctyl[1]­benzothieno­[3,2-b]­[1]­benzothiophene (C8-BTBT) is reported. We reveal that C8-BTBT bridges the perovskite film to the hole-transporting layer with reduced interfacial defects and improved charge carrier management. Moreover, such interfacial modification with air-stable C8-BTBT achieves a desirable and robust morphology of Spiro-OMeTAD by reducing the aggregates. Accordingly, C8-BTBT-treated devices exhibit a great enhancement to all photovoltaic performance characteristics with an absolute efficiency improvement exceeding 2%. The C8-BTBT-modified Spiro-OMeTAD enables decent thermal tolerance, which paves the way for enhancing the performance of Spiro-OMeTAD-based perovskite optoelectronics.

Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2AgBiBr6, shows attractive optical and electronic features, making it promising for high‐efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal‐engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs2AgBiBr6 under ambient conditions. The band‐gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first‐principles calculations indicate that enhanced Ag–Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band‐gap narrowing effect. This work provides new insights for achieving lead‐free double perovskites with suitable band gaps for optoelectronic applications.

Organic-inorganic hybrid perovskites, with a formula of ABX 3 , (A: cations, B: Pb, and X: halides), have recently attracted great attention in the solar-cell community for being efficient light absorbers. These perovskites show excellent physical and optoelectronic properties, such as ambipolar charge-carrier transport, long carrier diffusion length, and strong panchromatic light absorption; moreover, they are also solution processable. [1][2][3] The perovskitebased solar cell (PSC) has demonstrated impressive performance by showing an increase of the power conversion efficiency (PCE) from 3% to a certified 22% during the past few years. [4] The great success of PSCs is significantly attributed to the tremendous efforts in the perovskite compositional engineering, device-architecture design, solar-cell stability improvement, Hole transport matertial (HTM) as charge selective layer in perovskite solar cells (PSCs) plays an important role in achieving high power conversion efficiency (PCE). It is known that the dopants and additives are necessary in the HTM in order to improve the hole conductivity of the HTM as well as to obtain high efficiency in PSCs, but the additives can potentially induce device instability and poor device reproducibility. In this work a new strategy to design dopant-free HTMs has been presented by modifying the HTM to include charged moieties which are accompanied with counter ions. The device based on this ionic HTM X44 dos not need any additional doping and the device shows an impressive PCE of 16.2%. Detailed characterization suggests that the incorporated counter ions in X44 can significantly affect the hole conductivity and the homogeneity of the formed HTM thin film. The superior photovoltaic performance for X44 is attributed to both efficient hole transport and effective interfacial hole transfer in the solar cell device. This work provides important insights as regards the future design of new and efficient dopant free HTMs for photovotaics or other optoelectronic applications.

Adequate hole mobility is the prerequisite for dopant-free polymeric hole-transport materials (HTMs). Constraining the configurational variation of polymer chains to affordarigid and planar backbone can reduce unfavorable reorganization energy and improve hole mobility.H erein, an oncovalent conformational locking via S-O secondary interaction is exploited in ap henanthrocarbazole (PC)b ased polymeric HTM, PC6,t of ix the molecular geometry and significantly reduce reorganization energy.S ystematic studies on structurally explicit repeats to targeted polymers reveals that the broad and planar backbone of PC remarkably enhances pp stacking of adjacent polymers,f acilitating intermolecular charge transfer greatly.T he inserted "Lewis soft" oxygen atoms passivate the trap sites efficiently at the perovskite/HTM interface and further suppress interfacial recombination. Consequently,aPSC employing PC6 as adopant-free HTM offers an excellent power conversion efficiency of 22.2 %a nd significantly improved longevity,r endering it as one of the best PSCs based on dopant-free HTMs.