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A tetraaryl‐1,4‐dihydropyrrolo‐[3,2‐b]pyrroles (TAPP) moiety with the combination of two pyrrole rings and four phenyl moieties demonstrated strong electron‐donating ability and nonplanar configuration simultaneously. Once incorporated into the organic dyes as a novel electron donor, it was beneficial for the enhancement of light‐harvesting ability and suppression of electron recombination in the photovoltaic and photocatalysis systems. With the linkage of tunable conjugated bridges and electron acceptor, the corresponding organic dyes exhibited improved photovoltaic performance in dye‐sensitized solar cells and facilitated photocatalytic hydrogen generation with a highest turnover number (TON) of 4337. Through the detailed investigation of relationship between molecular structures and photovoltaic/photocatalysis property, the connection and difference in molecular design for these two systems are well explained, with the aim to promote the application of dye‐sensitized technology in various fields. TAPP dance: With the incorporation of tetraaryl‐1,4‐dihydropyrrolo‐[3,2‐b]pyrroles (TAPP) derivatives into organic dyes as novel electron donors, the optimized photovoltaic and photocatalysis performance is achieved by the efficient suppression of electron recombination in different conditions. [ABSTRACT FROM AUTHOR]

Abstract: Efficient metal‐halide perovskite solar cells (PSCs) with a regular structure typically use high‐temperature‐processed TiO2 electron‐transport layers (ETLs), which suffer from high electron recombination and inherent UV instability. Herein, we present low‐temperature solution‐processed lithium bis(trifluoromethanesulfonyl)imide (Li‐TFSI)‐doped C60 (Li‐C60) ETLs for high‐efficiency and UV‐stable planar PSCs with an n‐i‐p architecture. We found that simple Li‐TFSI doping ensured a better energy match between the active layer and the cathode, considerably enhanced the electron mobility of the ETL, and even improved CH3NH3PbI3 crystallization finally to increase the power conversion efficiency (PCE) from 15.3 to 17.8 % with a minor hysteresis effect. Moreover, it was demonstrated that replacing TiO2 with Li‐C60 resulted in PSCs that were much more stable under UV light under an air atmosphere with almost no degradation after 3000 h under a nitrogen atmosphere. [ABSTRACT FROM AUTHOR]

Electron recombination occurring at the TiO2/quantum dot sensitizer/electrolyte interface is the key reason for hindering further efficiency improvements to quantum dot sensitized solar cells (QDSCs). Polyoxometalate (POM) can act as an electron-transfer medium to decrease electron recombination in a photoelectric device owing to its excellent oxidation/reduction properties and thermostability. A POM/TiO2 electronic interface layer prepared by a simple layer-by-layer self-assembly method was added between fluorine-doped tin oxide (FTO) and mesoporous TiO2 in the photoanode of QDSCs, and the effect on the photovoltaic performance was systematically investigated. Photovoltaic experimental results and the electron transmission mechanism show that the POM/TiO2 electronic interface layer in the QDSCs can clearly suppress electron recombination, increase the electron lifetime, and result in smoother electron transmission. In summary, the best conversion efficiency of QDSCs with POM/TiO2 electronic interface layers increases to 8.02 %, which is an improvement of 25.1 % compared with QDSCs without POM/TiO2. This work first builds an electron-transfer bridge between FTO and the quantum dot sensitizer and paves the way for further improved efficiency of QDSCs. [ABSTRACT FROM AUTHOR]

We have recently found that in-diffusion of hydrogen into n-type Si crystals containing oxygen and carbon impurities can result in the formation of powerful recombination centers (M. Vaqueiro-Contreras et al., to appear in PSS RRL). Here, we describe a combination of first-principles calculations and electrical measurements to investigate the composition, structure, electrical activity and recombination mechanism of a carbon-oxygen-hydrogen complex (COH) in Si. We found a defect comprising a carbon-oxygen complex connected to an H atom whose location depends on the charge state of the complex, and showing a calculated acceptor level at Ev + 0.3 eV, a few meV away from the observations. Bistable carbon-oxygen-hydrogen complex in silicon. Carbon, oxygen, hydrogen, and silicon atoms are shown in gray, red, black, and white, respectively. [ABSTRACT FROM AUTHOR]

The move toward lower cost sources of solar silicon has intensified the efforts to investigate the possibilities of passivating or reducing the recombination activity caused by deep states associated with transition metals. This is particularly important for the case of the slow diffusing metals early in the periodic sequence which are not removed by conventional gettering. In this paper, we examine reactions between hydrogen and transition metals and discuss the possibility of such reactions during cell processing. We analyse the case of hydrogenation of iron in p-type Si and show that FeH can form under non-equilibrium conditions. We consider the electrical activity of the slow diffusing metals Ti, V, and Mo, how this is affected in the presence of hydrogen, and the stability of TM-H complexes formed. Finally, we discuss recent experiments which indicate that re-siting of some transition metals from the interstitial to substitutional site is possible in the presence of excess vacancies, leading to a reduction in recombination activity. Periodic ordering of the 3d, 4d, and 5d transition metals with adjacent columns of the periodic table. The metals with hydrogen complexes which have had their electronic properties reported in the literature or in this paper are highlighted in green. [ABSTRACT FROM AUTHOR]

4-Stilbenecarboxaldehyde (4SCA) at pH 3 was added to TiO2 anatase to form a new catalyst where the aldehyde carbonyl group reacts with the TiO2-OH to form the corresponding acetal (4SCA-TiO2). 4SCA-TiO2 significantly retards the electron recombination when it is illuminated with ultraviolet B light because of the formation of a stable radical anion·−4SCA-TiO2 that we have detected spectroelectrochemically. The light excited electron on the catalysis is transferred relatively slow to solution. Therefore, the electron transfer to solution is the rate-limiting step for water-dissolved organic compound degradation when 4SCA-TiO2 is used as photocatalyst. For instance, degradation rate constants using naphthalene (Naph) and p-nitrophenol (PNP) in an ample pH range support the proposal. Accordingly, rate constants are faster when the standard redox potential of the involved electron acceptor in the solution increases. In fact, this condition can be tuned to promote reactivity. The affinity between the organics being degraded and 4SCA-TiO2 also influences on the degradation rate constants. [ABSTRACT FROM AUTHOR]

The presence of copper contamination is known to severely degrade the minority carrier lifetime of p-type silicon upon exposure to illumination. In this contribution, we have analyzed the recombination activity of light-activated copper defects in deliberately Cu-contaminated p-type silicon by means of a recombination model that quantitatively defines the effect of metallic precipitates on minority carrier lifetime. The excellent agreement between the model and the experimental data indicates that (i) the formation of Cu precipitates is the probable root-cause behind Cu-LID and (ii) in the samples examined in this work, the precipitate radius varies between few to several tens of nm with corresponding densities estimated to be in the range of 108-1010 cm−3. Further evidence of these results was obtained from the analysis of temperature-dependent lifetime data. While applied here to light-activated copper defects, the procedure described in this article can be applied for characterizing lifetime-limiting precipitates originated by other transition metals (e.g., Fe or Ni). [ABSTRACT FROM AUTHOR]

Recent advances in dye-sensitized solar cells (DSSC), including the use of nanocarbons, resulted in breakthroughs relevant to both the academic and industrial sectors. Their relevance encompasses, on one hand, the development and integration of novel nanocarbon/dye hybrids for superior light-harvesting and improved charge injection properties and, on the other hand, the integration of nanocarbons into each part of DSSCs for enhancing the charge collection efficiency as well as the dye and electrolyte regeneration processes. In the context of the earlier, control over the electron injection and recombination rates is realized on the molecular level. In the context of the latter, i) the charge transport and charge collection efficiencies in the photoelectrode are increased, ii) the charge recombination processes are reduced, when used as a nanocarbon-based buffer layer, iii) the ion diffusion and catalytic effects into (quasi) solid-state electrolytes are improved, and iv) devices using Pt-free counter electrodes with similar device efficiencies are realized. Leading examples of nanocarbons are graphene, carbon black, multi-walled carbon nanotubes, and single-walled carbon nanotubes. In this review, the focus is on a novel carbon allotrope, namely single-walled carbon nanohorns (SWCNH), which is discussed in depth and in comparison with other nanocarbons. [ABSTRACT FROM AUTHOR]

Excess illumination damages the photosynthetic apparatus with severe implications with regard to plant productivity. Unlike model organisms, the growth of Chlorella ohadii, isolated from desert soil crust, remains unchanged and photosynthetic O2 evolution increases, even when exposed to irradiation twice that of maximal sunlight., Spectroscopic, biochemical and molecular approaches were applied to uncover the mechanisms involved., D1 protein in photosystem II ( PSII) is barely degraded, even when exposed to antibiotics that prevent its replenishment. Measurements of various PSII parameters indicate that this complex functions differently from that in model organisms and suggest that C. ohadii activates a nonradiative electron recombination route which minimizes singlet oxygen formation and the resulting photoinhibition. The light-harvesting antenna is very small and carotene composition is hardly affected by excess illumination. Instead of succumbing to photodamage, C. ohadii activates additional means to dissipate excess light energy. It undergoes major structural, compositional and physiological changes, leading to a large rise in photosynthetic rate, lipids and carbohydrate content and inorganic carbon cycling., The ability of C. ohadii to avoid photodamage relies on a modified function of PSII and the dissipation of excess reductants downstream of the photosynthetic reaction centers. The biotechnological potential as a gene source for crop plant improvement is self-evident. [ABSTRACT FROM AUTHOR]

Dye-sensitized solar cells equipped with cationic and neutral RuII-based sensitizers [Ru(ddpd){tpy(COOH)3}]2+ [12+; ddpd = N,N'-dimethyl-N,N'-di(pyridin-2-yl)pyridin-2,6-diamine, tpy(COOH)3 = 2,2''6',2''-terpyridine-4,4',4''-tricarboxylic acid] and [Ru(ddpd){tpy(COOH)(COO)2}] (2) with and without the coadsorbent chenodeoxycholic acid were constructed with I3 -/I- or the CoIII/II-based redox mediators [Co- (bpy)3]3+/2+ (33+/2+; bpy = 2,2'-bipyridine) and [Co- (ddpd)2]3+/2+ (43+/2+) in the presence of LiClO4 and 4-tert-butylpyridine. The best photovoltaic performance was achieved by using the 43+/2+ shuttle and the neutral sensitizer 2 without coadsorbent. The higher short-circuit photocurrent density and higher electron recombination lifetimes obtained with this combination suggest slow electron recombination kinetics at the TiO2 surface with the CoIII complex 43+. The slow electron transfer to 43+ is tentatively ascribed to the high-lying π* orbitals of the electron-rich ddpd ligands, which result in a weak electronic coupling. This contrasts with the faster recombination with 33+, which features the low-energy π* orbitals of the bpy ligands. [ABSTRACT FROM AUTHOR]

Ultrafast thermalized and hot-hole-transfer processes have been investigated in CdSe quantum dot (QD)/catechol composite systems in which hole transfer from photoexcited QDs to the catechols is thermodynamically favorable. A series of catechol derivatives were selected with different electron-donating and -withdrawing groups, and the effect of these groups on hole transfer and charge recombination (CR) dynamics has been investigated. The holetransfer time was determined using the fluorescence upconversion technique and found to be 2-10 ps depending on the molecular structure of the catechol derivatives. The hothole- transfer process was followed after monitoring 2S luminescence of CdSe QDs. Interestingly, hot-hole extraction was observed only in the CdSe/3-methoxycatechol (3-OCH3) composite system owing to the higher electron-donating property of the 3-methoxy group. To confirm the extraction of the hot hole and to monitor the CR reaction in CdSe QD/catechol composite systems, ultrafast transient absorption studies have been carried out. Ultrafast transient-absorption studies show that the bleach recovery kinetics of CdSe QD at the 2S excitonic position is much faster in the presence of 3-OCH3. This faster bleach recovery at the 2S position in CdSe/3-OCH3 suggests hot-hole transfer from CdSe QD to 3- OCH3. CR dynamics in CdSe QD/catechol composite systems was followed by monitoring the excitonic bleach at the 1S position and was found to decrease with free energy of the CR reaction. [ABSTRACT FROM AUTHOR]

One-electron reduction of mononuclear nonheme iron(III) hydroperoxo (FeIIIOOH) and iron(III) alkylperoxo (FeIIIOOR) complexes by ferrocene (Fc) derivatives resulted in the formation of the corresponding iron(IV) oxo complexes. The conversion rates were dependent on the concentration and oxidation potentials of the electron donors, thus indicating that the reduction of the iron(III) (hydro/alkyl)peroxo complexes to their one-electron reduced iron(II) (hydro/alkyl)peroxo species is the rate-determining step, followed by the heterolytic OO bond cleavage of the putative iron(II) (hydro/alkyl)peroxo species to give the iron(IV) oxo complexes. Product analysis supported the heterolytic OO bond-cleavage mechanism. The present results provide the first example showing the one-electron reduction of iron(III) (hydro/alkyl)peroxo complexes and the heterolytic OO bond cleavage of iron(II) (hydro/alkyl)peroxo species to form iron(IV) oxo intermediates which occur in nonheme iron enzymatic and Fenton reactions. [ABSTRACT FROM AUTHOR]

Hierarchical ZnO nanorods composed of interconnected nanoparticles, which were synthesized by controlling precursor concentrations in a solvothermally assisted process, were exploited as photoanodes in dye-sensitized solar cells (DSCs). The as-prepared hierarchical nanorods showed greatly enhanced light scattering compared to ZnO nanoparticles for boosting light harvesting while maintaining sufficient dye-adsorption capability. The charge-transfer characteristics were studied by electrochemical impedance measurements, and reduced electron recombination and longer electron lifetime were observed for the ZnO nanorods. Photovoltaic characterization demonstrated that DSCs utilizing the hierarchical nanorods significantly improved the overall conversion efficiency by 34 % compared to nanoparticle-based DSCs. [ABSTRACT FROM AUTHOR]

A general and convenient strategy is proposed for enhancing photovoltaic performance of aqueous dye-sensitized solar cells (DSCs) through the surface modification of titania using an organic alkyl silane. Introduction of octadecyltrichlorosilane on the surface of dyed titania photoanode as an organic barrier layer leads to the efficient suppression of electron recombination with oxidized cobalt species by restricting access of the cobalt redox couple to the titania surface. The champion ODTS-treated aqueous DSCs (0.25 m M ODTS in hexane for 5 min) exhibit a Voc of 821±4 mV and Jsc of 10.17±0.21 mA cm−2, yielding a record PCE of 5.64±0.10 %. This surface treatment thus serves as a promising post-dye strategy for improving the photovoltaic performance of other aqueous DSCs. [ABSTRACT FROM AUTHOR]

The co-sensitization of N719 with a cyclic thiourea functionalized organic dye, coded AZ5, for dye-sensitized solar cells (DSSCs) was demonstrated. Due to its intensive absorption in ultraviolet region, AZ5 could compensate the loss of light harvest induced by triiodide, thereby the short-circuit photocurrent density (Jsc) was increased for co-sensitized (N719+AZ5) DSSC. Moreover, the electron recombination and dye aggregation were retarded upon N719 cocktail co-sensitized with AZ5, thus the open-circuit voltage (Voc) of co-sensitized device was enhanced as well. The increased Jsc (17.9 mA ⋅ cm-2) combined with the enhanced Voc (698 mV) ultimately resulted in an improved power conversion efficiency (PCE) of 7.91% for co-sensitized DSSC, which was raised by 8.6% in comparison with that of N719 (PCE = 7.28%) sensitized alone. In addition, co-sensitized DSSC exhibited a better stability than that of N719 sensitized device probably due to the depression of dye desorption. [ABSTRACT FROM AUTHOR]

Electron recombination is one of the major loss factors in dye-sensitized solar cells (DSC), especially, with single electron outer sphere redox shuttle electrolyte. Insulating sub-nanometer oxide tunneling layers deposited by atomic layer deposition (ALD) are known to block the electron recombination, thereby leading to an increase in the open-circuit potential and the collection efficiency of the solar cell. A general perception in the DSC community is that any insulating oxide layer can block the recombination. However, in this work, it is unraveled that the insulating property of oxides alone is not sufficient. In addition, the properties such as the conduction band position and the oxidation state of the insulating oxide, the electronic structural modification induced to the underlying TiO2 mesoporous film, modification of surface charges (isoelectric point) and charge of the electrolyte species have to be considered. A complete photovoltaic study is done by depositing different cycles (by ALD) of four different insulating oxides (Ga2O3, ZrO2, Nb2O5, and Ta2O5) and their recombination characteristics, surface electronic properties, transport rate, and injection dynamics are investigated with a standard organic dye and Co2+/Co3+ redox mediator. A comparison is made with the conventional iodide/triiodide electrolyte. [ABSTRACT FROM AUTHOR]

The effect of 4,4′‐diaminodiphenylsulfone (DADPS) as a co‐additives in iodide/triiodide redox electrolyte on the performance of dye‐sensitized solar cell based on the 2‐cyano‐3‐(4‐(diphenylamino)phenyl)acrylic acid (TPA) and 2‐cyano‐3‐(2΄‐(5΄,10΄,15΄,20΄‐ tetraphenylporphyrinato Zinc (II)yl) acrylic acid (Zn‐1) dyes have been investigated. Compared withstandard electrolyte (0.1 M LiI, 0.05 M I2, 0.6 M 1‐butyl‐2,3‐dimethylimidazolium iodide (BDMII) and TBP (0.5, 1 M)), adding 0.5 M of DADPS, as a co‐additive, into the electrolyte system has caused increasing short current density (Jsc) and open‐circuit potential (Voc) consequently the energy conversion (η) improved. Electrochemical impedance results indicate adsorbing of DADPS on the titanium dioxide surface leads to an increase in the lifetime (τ). Adsorbing of DADPS on the semiconductor surface retards the interfacial charge recombination that has a beneficial effect on the Voc and Jsc. The results showed that amine groups of DADPS attach to the conduction band (CB) of TiO2 film and suppress the electron recombination process and as a result, it can be applied as a promising co‐additive in DSSCs. [ABSTRACT FROM AUTHOR]