Many enzymes use adaptive frameworks to preorganize substrates, accommodate various structural and electronic demands of intermediates, and accelerate related catalysis. Inspired by biological systems, a Ru-based molecular water oxidation catalyst containing a configurationally labile ligand [2,2′:6′,2″-terpyridine]-6,6″-disulfonate was designed to mimic enzymatic framework, in which the sulfonate coordination is highly flexible and functions as both an electron donor to stabilize high-valent Ru and a proton acceptor to accelerate water dissociation, thus boosting the catalytic water oxidation performance thermodynamically and kinetically. The combination of single-crystal X-ray analysis, various temperature NMR, electrochemical techniques, and DFT calculations was utilized to investigate the fundamental role of the self-adaptive ligand, demonstrating that the on-demand configurational changes give rise to fast catalytic kinetics with a turnover frequency (TOF) over 2000 s–1, which is compared to oxygen-evolving complex (OEC) in natural photosynthesis. 

Hole-transporting material (HTM) plays a paramount role in enhancing the photovltaic performance of perovskite solar cells (PSCs). Currently, the vast majority of these HTMs employed in PSCs are organic small molecules and polymers, yet the use of organic metal complexes in PSCs applications remains less explored. To date, most of reported HTMs require additional chemical additives (e.g. Li-TFSI, t-TBP) towards high performance, however, the introduction of additives decrease the PSCs device stability. Herein, an organic metal complex (Ni-TPA) is first developed as a dopant-free HTM applied in PSCs for its facile synthesis and efficient hole extract/transfer ability. Consequently, the dopant-free Ni-TPAbased device achieves a champion efficiency of 17.89%, which is superior to that of pristine SpiroOMeTAD (14.25%). Furthermore, we introduce a double HTM layer with a graded energy bandgap containing a Ni-TPA layer and a CuSCN layer into PSCs, the non-encapsulated PSCs based on the Ni-TPA/ CuSCN layers affords impressive efficiency up to 20.39% and maintains 96% of the initial PCE after 1000 h at a relative humidity around 40%. The results have demonstrated that metal organic complexes represent a great promise for designing new dopant-free HTMs towards highly stable PSCs.

Isolation of RuIII-bda (17-electron specie) complex with an aqua ligand (2-electron donor) is challenging due to violation of the 18-electron rule. Although considerable efforts have been dedicated to mechanistic studies of water oxidation by the Ru-bda family, the structure and initial formation of the RuIII-bda aqua complex are still controversial. Herein, we challenge this often overlooked step by designing a pocket-shape Ru-based complex 1. The computational studies showed that 1 possesses the crucial hydrophobicity at the RuV(O) state as well as similar probability of access of terminal O to solvent water molecules when compared with classic Ru-bda catalysts. Through characterization of single-crystal structures at the RuII and RuIII states, a pseudo seven-coordinate “ready-to-go” aqua ligand with RuIII...O distance of 3.62 Å was observed. This aqua ligand was also found to be part of a formed hydrogen-bonding network, providing a good indication of how the RuIII-OH2 complex is formed.

The outer coordination sphere of metalloenzyme often plays an important role in its high catalytic activity, however, this principle is rarely considered in the design of man-made molecular catalysts. Herein, four Ru-bda based molecular water oxidation catalysts with well-defined outer spheres are designed and synthesized. Experimental and theoretical studies showed that the hydrophobic environment around the Ru center could lead to thermodynamic stabilization of the high-valent intermediates and kinetic acceleration of the proton transfer process during catalytic water oxidation. By this outer sphere stabilization, a 6-fold rate increase for water oxidation catalysis has been achieved. 

A new crosslinked polymer, called P65, with appropriate photo-electrochemical, opto-electronic, and thermal properties, has been designed and synthesized as an efficient, dopant-free, hole-transport material (HTM) for n-i-p type planar perovskite solar cells (PSCs). P65 is obtained from a low-cost and easily synthesized spiro[fluorene-9,9′-xanthene]-3′,6′-diol (SFX-OH)-based monomer X65 through a free-radical polymerization reaction. The combination of a three-dimensional (3D) SFX core unit, hole-transport methoxydiphenylamine group, and crosslinked polyvinyl network provides P65 with good solubility and excellent film-forming properties. By employing P65 as a dopant-free hole-transport layer in conventional n-i-p type PSCs, a power conversion efficiency (PCE) of up to 17.7% is achieved. To the best of our knowledge, this is the first time a 3D, crosslinked, polymeric dopant-free HTM has been reported for use in conventional n-i-p type PSCs. This study provides a new strategy for the future development of a 3D crosslinked polymeric dopant-free HTM with a simple synthetic route and low-cost for commercial, large-scale applications in future PSCs.

Electron transport layer (ETL)/perovskite interface passivation is particularly challenging because of the use of polar solvents (e.g., DMF) for perovskite solution deposition, which usually destroy the bottom as-formed defect passivation layers. Herein, a novel multi-functional composite ETL, NH2-ZnO@SnO2, is prepared by mixing amino-capped ZnO (NH2-ZnO) nanocrystals (NCs) with SnO2 nanoparticles. The best-performing PSCs on the basis of NH2-ZnO@SnO2 achieve efficiency of 22.52%, which is significantly higher than that of the pristine SnO2 counterpart (18.45%) The enhanced performance of the NH2-ZnO@SnO2 ETL can be attributed to higher electron extraction capacity, better energy-level alignment with perovskite material, and more efficient carrier transport in device. Most important, the NH2 groups on the surface of ZnO NCs can effectively passivate the under-coordinated Pb2+ ions from perovskite films, thus reducing charge recombination at ETL/perovskite interface. The results suggest that NH2-ZnO NCs@SnO2 composite is a promising ETL for improving the performance of PSCs.

Understanding the seven coordination and O–O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earth-abundant metals. This work reports the synthesis, characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda (H2bnda = 2,2′-bi(nicotinic acid)-6,6′-dicarboxylic acid) featuring steric hindrance and enhanced hydrophilicity on the backbone. Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda (H2bda = 2,2ʹ-bipyridine-6,6ʹ-dicarboxylic acid), Ru-pda (H2pda = 1,10-phenanthroline-2,9-dicarboxylic acid), and Ru-biqa (H2biqa = (1,1ʹ-biisoquinoline)-3,3ʹ-dicarboxylic acid), we emphasized that seven coordination clearly determines presence of RuV[dbnd]O with high spin density on the ORuV[dbnd]O atom, i.e. oxo with radical properties, which is one of the necessary conditions for reacting through the O–O coupling pathway. However, an additional factor to make the condition sufficient is the favorable intermolecular face-to-face interaction for the generation of the pre-reactive [RuV[dbnd]O···O[dbnd]RuV], which may be significantly influenced by the secondary coordination environments. This work provides a new understanding of the structure–activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O–O bond formation.

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. 

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)Br-6, 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.

Research on perovskite solar cells (PSCs) has undergone dramatic development since the first cells were reported in 2009, and the past decade has witnessed a significant breakthrough on their power conversion efficiencies (PCEs) from 3.8% to 25%. However, the large-scale industrialization of PSCs is still far from an easy task, due to the scarcity of high-performance and low-cost organic hole-transport materials (HTMs). Thus, the development of new generation HTMs is highly desired.

The studies in this thesis aim at developing novel, inexpensive and easily synthesizable organic HTMs for application in efficient PSCs. A series of HTMs from small molecules to polymers, from doped to dopant-free were designed, synthesized and tested, to further improve the stability and reduce the cost.

In Chapter 1 and Chapter 2, a brief introduction to PSCs, HTMs as well as the characterization methods used in this thesis are presented.

In Chapter 3 and Chapter 4, the design and synthesis of a series of carbazole- based and spiro[fluorene-9,9'-xanthene] (SFX)-based HTMs is described. For these HTMs, the influence of substitution position, linking topology, pendant group and molecular size on the optical and electronic properties was systematically investigated, as well as their performance in solar cells.

In Chapter 5, two small molecular HTMs based on extended SFX skeletons were introduced for the application in dopant-free PSCs. The effect of the extended conjugation core unit and molecular size on the electrochemical and optical properties, hole mobility, conductivity, molecular packing and PSC performance was studied in detail.

In Chapter 6, a crosslinked SFX-based polymer was designed and synthesized as an efficient, low-cost, dopant-free HTM for conventional n-i-p type PSCs. The photoelectrochemical, optoelectronic and thermal properties of the designed polymer and the photovoltaic performance of the devices are discussed.

Forskning om perovskitsolceller (PSC:er) har genomgått en dramatisk utveckling sedan de första cellerna rapporterades 2009, och det senaste decenniet har sett ett betydande genombrott i deras effektomvandlingseffektivitet (PCE) från 3,8% till 25%. Den storskaliga industrialiseringen av PSC:er är emellertid fortfarande långt ifrån en enkel uppgift på grund av brist på högpresterande och billiga organiska håltransportmaterial (HTM). Därför är utvecklingen av nya generationer HTM önskvärt.

Studierna i denna avhandling syftar till att utveckla nya, billiga och lättsyntetiserbara organiska HTM:er för användning i effektiva PSC:er. En serie HTM:er från små molekyler till polymerer, från dopade till dopningsfria konstruerades, syntetiserades och testades för att ytterligare förbättra stabiliteten och minska kostnaderna.

I kapitel 1 och kapitel 2 presenteras en kort introduktion av PSC:er, HTM såväl som karakteriseringsmetoderna som används i denna avhandling.

I kapitel 3 och kapitel 4 rapporteras designen och syntesen av en serie karbazol-baserade och spiro[fluoren-9,9'-xanten] (SFX)-baserade HTM. Dessutom undersöktes systematiskt påverkan av substitutionsposition, koppling av topologi, hänggrupp och molekylstorlek på de optiska och elektroniska egenskaperna, liksom solcellsprestanda.

I kapitel 5 designades och syntetiserades två små molekylära HTM baserade på ett utökat SFX-skelett för användning på dopningsfria PSC:er. Effekten av den utökade konjugeringskärnenheten och molekylstorleken på de elektrokemiska och optiska egenskaperna, hålmobilitet, konduktivitet, molekylär packning, liksom tillämpningen i PSC:er studerades i detalj.

I kapitel 6 designades och syntetiserades en tvärbunden SFX-baserad polymer som en effektiv, lågkostnads dopningsfri HTM för konventionella PSC:er av ni-p-typ. De fotoelektrokemiska, optoelektroniska och termiska egenskaperna hos den utformade polymeren och fotovoltaiska prestandan diskuterades.