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.

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.

The dioxygen formation mechanism of biological water oxidation in nature has long been the focus of argument; many diverse mechanistic hypotheses have been proposed. Based on a recent breakthrough in the resolution of the electronic and structural properties of the oxygen-evolving complex in the S state, our density functional theory (DFT) calculations reveal that the open-cubane oxo-oxyl coupling mechanism, whose substrates preferably originate from W2 and O5 in the S state, emerges as the best candidate for O-O bond formation in the S state. This is justified by the overwhelming energetic superiority of this mechanism over alternative mechanisms in both the isomeric open and closed-cubane forms of the MnCaO cluster; spin-dependent reactivity rooted in variable magnetic couplings was found to play an essential role. Importantly, this oxygen evolution mechanism is supported by the recent discovery of femtosecond X-ray free electron lasers (XFEL), and the origin of the observed structural changes from the S to S state has been analyzed. In this view, we corroborate the proposed water binding mechanism during S-S transition and correlate the theoretical models with experimental findings from aspects of substrate selectivity according to water exchange kinetics. This theoretical consequence for native metalloenzymes may serve as a significant guide for improving the design and synthesis of biomimetic materials in the field of photocatalytic water splitting.

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.

No abstract

No abstract

No abstract

Ammonia as a water analogue can bind to the MnCaO cluster of the oxygen-evolving complex in concomitance with ligand substitution and underlying structural transformation. On account of current controversies of the binding site and the absence of the viewpoint of reactivity and mechanistic proofs, we have investigated three modes of NH binding based on our elaborations of the possible reaction mechanisms, in correspondence with experimental observation for the NH-altered g ≈ 2.0 EPR multiline signal. Broken-symmetry density functional theory was employed to construct all the spin surfaces. As a result, we rule out the O5 substitution strategy owing to the impenetrable free energy barrier exceeding 30 kcal mol, and alternative routes to destroy the O5 bridge are also blocked. The W1 substitution mechanism is shown to be quite facile, with the barrier not above 11.4 kcal mol. For the Mn4 addition scheme, the 'redox switch mechanism' was not implemented by our model, and the effective ways found render 15-22 kcal mol energetic disadvantage by contrast. Consequently, it is strongly in favor of the W1 substitution mechanism for its overwhelming superiority in reactivity, reaching a consensus with the new pulse EPR conclusion. Then, we point out that ammonia departure occurs in the S' state, with the O-O bonding but unreleased molecular O. In the meantime, we propose two alternative channels for water binding in the S' state and expound the significance to substrate selectivity. Ultimately, implications for the mechanism of O-O bond formation are discussed and all the remaining options are listed for future explorations.