Conductivite electrique de sels doubles du type iodure d'argent—diiodures de piperazinium et de N, N′-alkyl-piperazinium

The electrical conductivity has been studied for four binary systems of the type silver iodide—piperazinium or N, N′-disubstituted piperazinium diiodides. At 25 °C, the conductivity shows a maximum of ≈ 0.1 (ohm cm)^?1 for the system silver iodide—N, N′ tetramethylpiperazinium diiodide at 93.25% mol silver iodide. The ionic nature of the conductivity has been proven.     

Organic solar cells consisting of stacked amine–thiophene copolymer and 3,4,9,10-perylenetetracarboxyl-bis-benzimidazole layers

Organic solar cells were fabricated using a new amine–bithiophene copolymer as an electron donor layer and 3,4,9,10-perylenetetracarboxyl-bis-benzimidazole (PV) as an electron acceptor layer. The amine–thiophene copolymer, poly{(9,9-dioctylfluorene-2,7-diyl)-co-[N,N′-bis(4-tert-butylphenyl)benzidine-N,N′-bis(phenylene-4,4′-diyl)]-co-(2,2′-bithiophene-5,5′-diyl)} (PF8-TPD-T2), had a glass transition temperature (T_g) at about 77 °C, and exhibited liquid crystalline states and a high hole mobility. The rigid bithiophene units in the polymer chain are probably responsible for the formation of the liquid crystalline states and the high hole mobility. A solar cell made of the PF8-TPD-T2 copolymer and PV layers showed a photocurrent density of 0.99 mA/cm², an open-circuit voltage of 0.61 V, and an energy conversion efficiency of 0.332%. The photocurrent of the solar cells was generated at both the copolymer and PV layers, and the copolymer layer was the main contributor to photocurrent when the thickness of the polymer was about 17 nm. After annealing the solar cells at temperatures well above the glass transition temperature (T_g) of the copolymer, the photocurrent action spectra of the solar cells were broadened and the performance was improved. The changes were mostly due to the increased contribution of the PV layer to the photocurrent by the annealing.     

Estimation of global and diffuse irradiation from sunshine duration and atmospheric water vapour content

Following Garg and Garg, atmospheric water vapour content or specific humidity W_at is used along with sunshine duration to obtain a relation to estimate the global irradiation G using data for stations near sea level only of north and central India. The method is extended to find D, the diffuse irradiation. The resulting equations are G = G₀(0.394+0.364 n/N′−0.0035 W_at)D = G₀(0.306+0.165 n/N′+0.0025 W_at) where N′ is the maximum duration for which the Campbell-Stokes sunshine recorder is active and G₀ is the extraterrestrial irradiation. The deviations are compared to those obtained by Mani and Rangarajan using Hay's formulae for G and D and also to those obtained by Garg and Garg for G.     

Photochemical electron transfer mechanism in the quenching of FMN by N,N,N′,N′-tetramethyl-p-phenylene diamine

The mechanisms of fluorescence quenching of Flavin Mononucleotide (FMN) by N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) and oxygen have been studied in non-aqueous and aqueous media. The rate constant k_Q, for the quenching reaction has been measured by monitoring the fluorescence intensity of FMN (λ_max = 530 nm) as a function of the quencher concentration; the lifetime of the excited singlet state of FMN is estimated using a pulsed nitrogen laser. On the basis of the data obtained in this study the following electron transfer mechanism is proposed for the quenching reaction in non-aqueous media

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Unlike the case of fluorescence quenching of aromatic hydrocarbons by amines where triplet states of hydrocarbons are produced through the radical reaction, the electron transfer reaction of FMN⁻ and TMPD⁺ does not produce the triplet states of either of the species (E_T(FMN) = 2.05 eV and E_T(TMPD) = 2.96 eV). This difference is explained by the reaction free energy being less than the energy of the triplet states. Further, experiments carried out in electrochemiluminescence by generating FMN⁻ and TMPD⁺ does not produce emission by radical ion annihilation reaction. Marcus theory of electron transfer reactions has been used to understand more about the quenching reaction. In aqueous media, exciplex formation is postulated in the fluorescence quenching of FMN by oxygen.     

A technique to compare polythiophene solid-state dye sensitized TiO2 solar cells to liquid junction devices

In this communication, we report on a technique to fabricate solid-state polythiophene-based dye sensitized solar cells (DSSCs) that can be directly compared to analogous liquid junction devices. The device configuration is based on non-porous TiO₂ thin films and one of the three undoped polythiophene hole conductors: poly[3-(11 diethylphosphorylundecyl) thiophene], P3PUT, poly(4-undecyl-2,2′-bithiophene), P4UBT, or poly(3-undecyl-2,2′-bithiophene), P3UBT. These polymers were spin coated and cast from organic solutions onto the TiO₂ films. The dense TiO₂ thin films (ca. 30 nm) were deposited on conductive glass via facile spray pyrolysis and sol–gel techniques. After that, cis-(SCN)₂ Bis(2,2′ bipyridyl-4,4′-dicarboxylate) ruthenium(II) (a.k.a. Ru N3 dye) was adsorbed on the TiO₂ surface, and the polythiophenes were utilized as hole conductors in a simplified solar cell geometry. The results were compared to the control DSSC device made with dense TiO₂ and a liquid electrolyte, or 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (a.k.a. Spiro-MeOTAD). The polythiophenes exhibited bandgaps in the range 1.9–2.0 eV, and HOMO energy levels of approximately 5 eV (vs. vacuum). The P3PUT DSSC device exhibited an AM1.5 V_OC=0.8 V, a J_SC=0.1 mA/cm², as well as an IPCE=0.5–1%. The AM1.5 short-circuit photocurrents and quantum efficiencies for DSSCs made with the polythiophenes, the Spiro-MeOTAD and the standard liquid electrolyte (I⁻/I₃⁻) were found to be identical within the limits of experimental uncertainty and reproducibility. Our results indicate that a solid-state replacement to the liquid junction is not necessarily limited by the fundamental aspect of hole transfer, one of the three fundamental aspects that must be met for an efficient DSSC. Rather than suggest that P3UBT or P4UBT could be used to create efficient “organic solar cells” with the exclusion of the Ru dye, we suggest that transparent thiophene compounds could be attractive candidates for high-surface area solid-state DSSCs, and that the technique presented can be applied to other hole conductors. It can allow a verification of one of the things necessary for the DSSC, so that parallel studies using high-surface area materials can proceed with confidence.     

On the correlations between collector efficiency factor and material content of parallel flow flat-plate solar collectors

The collector efficiency factor F^′, besides the collector heat loss coefficient U_L, characterizes the thermal quality of a solar collector. As F^′ is strongly influenced by the tube distance w and the absorber plate thickness δ, F^′ is also correlated with the material content of absorber plus tubing. Due to the future mass production of collectors and to the restricted copper resources (in the literature, a range until 2026 is given), the role of material savings can be expected to become more and more important. This paper focuses on the correlations between F^′ and the material content of absorber and tubing for flat-plate collectors with the fin-and-tube geometry. The correlations between w, δ, F^′ and material content are presented in a new type of nomograph. This nomograph indicates the values of w and δ that minimize the material content (for a given F^′). For a typical absorber with F^′=0.90, material savings of 25% can theoretically be achieved without any deterioration of F^′, by reducing the absorber plate thickness and the tube distance. The resulting plate thickness is below 0.1 mm; the respective tube distance will be about 7 cm. Practical restrictions are discussed. In a sensitivity analysis, the influence of different parameters on F^′ is investigated. The most important parameters are w, U_L,δ and the Reynolds number. The technique chosen for contacting tube and absorber has only a minor influence on F^′.     

Photoelectric behavior of nanocrystalline TiO2 electrode with a novel terpyridyl ruthenium complex

The photoelectric behavior of a black dye, tris (isothiocyanato)-[N-(2,2′:6′,2″-terpyridine-4′-(4-carboxylic acid) phenyl)] ruthenium (II) complex, was examined under different conditions. The dye was adsorbed on nanocrystalline TiO₂ surface strongly and generated incident monochromatic photon-to-current conversion efficiency (IPCE) of about 90% at maximum absorption wavelength and greater than 20% in the near-IR region. A sandwich-type solar cell fabricated by this dye-sensitized nanocrystalline TiO₂ film generated 6.1 mAcm⁻² of short-circuit photocurrent, 0.58 V of open-circuit photovoltage and 2.9% of overall yield under irradiation of white light (78.0 mWcm⁻²) from a Xe lamp. Since the title dye shows better photoresponse than the N3 dye in the near-IR region, it would be a promising panchromatic sensitizer after optimization.     

An EQCM study for a novel aromatic poly(amine-imide) electrochromic thin film

A new aromatic poly(amine-imide) electrochromic thin film synthesized with N,N-bis(4-aminophenyl)-N′,N′-diphenyl-1,4-phenylenediamine and 3,3′,4,4′-benzo-phenonetetra carboxylic dianhydride, abbreviated as poly(PD-BCD), was studied. The poly(PD-BCD) thin-film electrode has been characterized by cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM). As the polymer chain acquires positive charge during the oxidation of poly(PD-BCD) to its radical cation state or dication state, the anions would insert into the polymer matrix in order to neutralize the charge. However, when the electrodes were cycled in electrolytes containing different cations, including 0.1 M LiClO₄/acetonitrile (ACN), 0.1 M NaClO₄/ACN and 0.1 M TBAClO₄/ACN, the experimental results revealed two mechanisms for the redox reaction. A plot of mass change (Δm) vs. accumulated charge (Q) gave a slope, from which the electrochromic mechanism can be extracted. The slopes of Δm–Q obtained from the CV–EQCM measurements in three electrolytes were different for the first redox stage, but the slopes were almost the same for the second redox stage. This means that, in addition to the involvement of anions, cations also play an important role in the first redox stage, however, the role of the cations is less in the second stage. Moreover, two reaction mechanisms for the two reaction stages of poly(PD-BCD) are proposed in this study.     

Low band gap poly-thienopyrazines for solar cells—Introducing the 11-thia-9,13-diaza-cyclopenta[b]triphenylenes

The chemistry of the thienopyrazines has been explored with the aim of producing new low band gap polymers. 5,7-Di-(thiophen-2-yl)-thieno[3,4-b]pyrazines substituted in the pyrazine ring with alkyl groups, aryl groups and fused aromatic rings have been prepared and characterized. The electronic spectra show a great variation in the longest wavelength absorption band as a consequence of this substitution. A special case is the 11-thia-9,13-diaza-cyclopenta[b]triphenylene prepared by condensation of 3′,4′-diamino-[2,2′,5′,2″]terthiophene with phenanthrene-9,10-quinone. Alkyl substitution of the most promising monomers were carried out using the Kumada coupling and these were copolymerized with either 2,5-bis(trimethylstannyl)thiophene or 3-(3,7,11-trimethyl-dodecyl)-2,5-bis-trimethylstannyl-thiophene to form six new low band gap polymers: RISO-GREEN 1–3 and RISO-BROWN 1–3. The band gaps of these polymers were estimated from the UV–visible absorption spectra and found to be ca. 1.3 eV. Preliminary results from photovoltaic device fabrication with mixtures of the six polymers with either [60]PCBM or [70]PCBM gave modest efficiencies of max 0.2% with open circuit voltages V_oc of 0.3 V and short circuit currents J_sc (1000 Wm⁻² AM1.5) in the range of 2 mA cm⁻².     

Highly efficient solid-state dye-sensitized TiO2 solar cells via control of retardation of recombination using novel donor-antenna dyes

Two series of heteroleptic tris(bipyridyl)Ru(II) and bis(bipyridyl)(NCS)₂Ru(II) complexes have been synthesized and characterized. This is a part of a new concept of covalent linkage of donor-antenna groups, e.g., triphenylamine or N,N′-bis(phenyl)-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) to Ru(II) dye center. For the covalent attachment of donor units, a multi-step synthesis was carried out starting from 4,4′-dimethyl-2,2′-bipyridine followed by chlorination and Wittig reaction with donor aldehydes. This was followed either by a metallation reaction using bis(4,4′-dicarboxy-2,2′-bipyridyl)Ru(II)dichloride ((bpy(COOH)₂Ru(II)2Cl₂ 2H₂O) as precursor to get tris(bipyridyl) dyes or by a one pot synthesis starting from dichloro(p-cymene)Ru(II) dimer resulting in bis(bipyridyl)(NCS)₂ dyes. The complexes (bpy(COOH)₂)₂(bpyMe₂)Ru(II) 2PF₆ and (bpy(COOH)₂)(bpyMe₂)(NCS)₂Ru(II) without donor-antenna groups were also prepared to study and compare the properties. The influence of donor-antenna groups in these complexes was studied using UV–Vis spectroscopy and cyclic voltammetry. The heteroleptic complexes carrying donor groups show appreciably broad absorption ranges and extraordinarily high extinction coefficients. These high extinction coefficients are explained as due to the extended delocalization of π-electrons in the donor-antenna ligands. The HOMO/LUMO energy values obtained from cyclic voltammetry support the multi-step charge transfer cascade possible in these donor-antenna dyes. Examples of solid-state dye-sensitized solar cell utilizing these novel donor-antenna dyes revealed spectacular performances of power conversion efficiencies of up to 3.4%, for the dye carrying a TPD donor group as measured under AM 1.5 spectral conditions. This is attributed to highly efficient light harvesting of these novel dyes and the improved charge transfer dynamics at TiO₂–dye and dye–hole conductor interfaces.     

A novel organic n-type material: fluorinated perylene diimide

In order to increase the dissociation efficiency of electron–hole pairs (excitons) in organic solar cells, and to enhance the solubility of organic materials for easy fabrication, a novel perylene diimide with multiple strongly electron-withdrawing F atoms, N,N′-diperfluorophenyl-3,4,9,10-perylenetetracarboxylic diimide (DFPP), was designed and synthesized. The solubility of DFPP was improved greatly compared to its non-fluorinated parent, N,N′-diphenyl-3,4,9,10-perylenetetracarboxylic diimide (DPP), which might relate to the spatial arrangement of the phenyl versus the pentafluorophenyl groups. The field-effect-transistor (FET) with spin-coated DFPP film as transport layer was prepared, and its electron mobility was measured as 1.29×10⁻⁵ cm² V⁻¹ s⁻¹, 3.4 times higher than that from vacuum-deposited DPP film, demonstrating its potential applications in organic optoelectronic devices.     

Solid-state dye-sensitized solar cells based on spiro-MeOTAD

Dye-sensitized solar cells (DSC) could become low cost alternatives to inorganic photovoltaic devices. The DSC studied here use the hole transporting material 2,2′7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-MeOTAD). The effect of t-butyl pyridine (t-BP) on the current–voltage characteristics of thin layer cells were investigated using complete cells and cells consisting only of the TiO₂ blocking layer. In addition, absorption spectroscopy was used to study the effect t-BP has on the doping density of spiro-MeOTAD. The results are correlated with device performance.     

Characterisation and application of new carboxylic acid-functionalised ruthenium complexes as dye-sensitisers for solar cells

A series of ruthenium complexes with and without TiO₂ anchoring carboxylic acid groups have been synthesised and characterised using nuclear magnetic resonance (NMR), UV–vis and luminescence. These complexes were adsorbed on thin films of the wide band-gap semiconductor anatase and were tested as photosensitisers under standard conditions. I/V characteristics of such devices revealed superior performance of the non-symmetric complexes [4′-(4-bromophenyl)-[2,2′; 6′,2″] terpyridine]Ru(II) [4′-(4-bromophenyl)-[2,2′; 6′,2″] terpyridine-4,4″-dicarboxylic acid] and [2,2′; 6′,2″] terpyridine Ru(II) [2,2′; 6′,2″] terpyridine-4′-carboxylic acid with a maximum output power 0.016 mW cm⁻² under illumination at 100 mW cm⁻² AM1.5 and efficiencies 3 times higher than the symmetric complexes.     

Structure and photoelectrochemical properties of ruthenium(II) polypyridyl complexes as sensitizers for nanocrystalline TiO2 electrodes

The relationship between the structures and photoelectrochemical properties of two dyes, cis-dithiocyanato-N,N′-bis(4,4′-dicarboxyl-2,2′-bipyridyl) Ru(II) and cis-dithiocyanato-(4,4′-dicarboxyl-2,2′-bipyridyl)-(4,4′-di((N,N′-methylphenylamino)methylene)-2,2′-bipyridyl) Ru(II), was examined and compared under the same conditions. Data show that the photophysical properties (including molar extinction coefficients and excited-state lifetimes) and photoelectrochemical properties (including short-circuit photocurrent, open-circuit photovoltage, incident monochromatic photon to current conversion efficiency, overall energy conversion yield (η) and transient photocurrent) were changed greatly only due to an acceptor replaced by a donor in one of polypyridyl of the Ru(II) complex, suggesting that the molecular design in energy conversion is very sensitive.     

Derivation of efficiency factors for uneven irradiation on a fin absorber

In the equation for thermal energy output from a flat-plate solar collector (written as a function of the collector mean heat carrier temperature), both the gain and the loss terms are multiplied by the collector efficiency factor, F^′. For a concentrating collector with an uneven (non-uniform) irradiation on the absorber, the efficiency factor for the gain term, here called the optical efficiency factor, F^′_c, is different from F^′ and is a function of the irradiation distribution on the absorber. If the heat loss coefficient is assumed to be constant across the fin, the optical efficiency factor for absorbed irradiation at a certain distance from the edge of the absorber is independent of absorbed irradiation at other locations and can therefore be expressed F^′_c(x), where x is the distance from the edge of the absorber. Close to the edge, F^′_c(x)<F^′ and close to the pipe, F^′_c(x)>F^′. In this paper formulas are derived for calculating F^′_c(x) for a fin absorber with constant fin thickness. By weighting F^′_c(x) with the absorbed irradiance, S_c(x), and integrating across the absorber, an absorber average optical efficiency factor, F^′_c,a, is obtained. This value replaces F^′ in the gain term of the equation for thermal energy output. If, instead, the energy output equation is expressed as a function of the inlet temperature, F^′_c,a can be used for calculating a corresponding heat removal factor for uneven irradiation, F_R,c. Formulas for calculating the temperature distribution across the absorber for the case of uneven irradiation are also derived.     

Photooxidation studies with perylenediimides in solution, PVC and sol–gel thin films under concentrated sun light

The singlet oxygen quantum yields (_Δ), LUMO energy levels (eV), photo stabilities under Xe-lamp irradiation of N,N′-di-dodecyl-3,4,9,10-bis(dicarboximide)perylene and N,N′-di-(1-dehydroabiethyl)-3,4,9,10-bis(dicarboximide)perylene, N-DODEPER and ABIPER, respectively, in different host matrices (solution, PVC and sol–gel matrix) are determined. Quenching of their emission by KI is found to give k_q values of 3.5–37.4 × 10⁹ M⁻¹ s⁻¹. Quenching is more efficient in solution phase than it is in immobilized phases. _Δ’s of ABIPER and N-DODEPER are in negligible range, 0.090 and 0.095, respectively. The LUMO energy levels determined by cyclic voltammetric studies are 3.65 and 3.49 eV for ABIPER and N-DODEPER, respectively. Neither ABIPER nor N-DODEPER showed degradation tendency in sol–gel matrix.Photooxidation of α-terpinene is performed with ABIPER and N-DODEPER as photosensitizers, both in acetonitrile solutions and immobilized phases (PVC and sol–gel host matrices) by the use of two different irradiation sources, Na lamp and concentrated sun light. The photosensitizers exhibited different activities on the product profile, which were strongly dependent on the irradiation source, period of irradiation and the phase that the sensitizers were placed (solution or immobilized phases). Product analysis results point that in immobilized phases of PVC films 3,6-dioxoheptanal is the major product. In solution and immobilized phase of sol–gel ascaridol is the most abundant product. Superoxide anion radical, forms as reactive intermediate at photoinduced electron transfer process, directs the primary mechanistic step of photooxidations. A secondary mechanistic step is being proposed for the clarification of product formations.     

Structural and transport evolution in the LixAg2V4O11 system

We investigated the effect of inserting lithium into Ag₂V₄O₁₁ (-SVO) on the structure, electronic properties and redox committed by combining in situ XRD measurements, ESR spectroscopy and 4 probes DC conductivity coupled with thermopower measurements. The electrochemical discharge occurs in three consecutive steps above 2 V (vs. Li⁺/Li). The first one, between 0 < x < 0.7 in Li_x-SVO, has been ascribed to the V⁵⁺ reduction through a solid solution mechanism. This reduction competes with a Li⁺/Ag⁺ displacement reaction which leads to a structural collapse owing to the ionic radii mismatch between the withdrawn Ag⁺ and the inserted Li⁺. The silver reduction progresses continuously with two different slopes along two composition–potential plateaus at 2.81 V and 2.55 V. Finally, the reduction continues until we obtain an amorphous structure with V⁴⁺ and a of V³⁺. Although, the silver re-enters the structure during the subsequent recharge, the original structure is not recovered. The reduction of silver forming silver metal nano-clusters acts to increase the electronic conductivity from 3.8 × 10⁻⁵ S cm⁻¹ to 1.4 × 10⁻³ S cm⁻¹. In complement to this study, we also report on a low temperature hydro-(solvo)-thermal approach using HF_(aq) as a mineralizer, which enables the synthesis of nano-sized -SVO particles that exhibit superior electrochemical performances compared to conventional particles synthesized by solid-state reaction.     

P3HT/TiO2 bulk-heterojunction solar cell sensitized by a perylene derivative

In this work, a new type of dye-sensitized bulk-heterojunction hybrid solar cells has been developed. The heterojunction films were prepared to contain poly(3-hexylthiophene) (P3HT), N,N′-diphenyl glyoxaline-3,4,9,10-perylene tetracarboxylic acid diacidamide (PDI) and TiO₂. In the architecture, TiO₂ and P3HT were designed to act as the electron acceptor and donor. PDI was used as sensitizer to enhance the photon absorption. Results showed that by incorporation of PDI in the P3HT/TiO₂ composite, the light absorption, exciton separation and photocurrent under white light were dramatically enhanced. Solar decay analyses showed that devices contained TiO₂ required 12 h to obtain maximum current density and the addition of PDI did not affect the solar decay behavior and stability of device composed of P3HT/TiO₂. The devices of P3HT, P3HT/TiO₂, P3HT/TiO₂/PDI could work for 5, 42, 45 h under continuous white light illumination (100 mW/m²) under the ambient condition.     

Computation of solar radiation from observations of cloud cover

Techniques of computation of global and diffuse solar radiation from the daily duration of bright sunshine and cloud cover are well-known. However, since radiation computations from cloud cover data provide rather imprecise results, this method is resorted to only when sunshine data are not available. To obtain a better idea of the inverse relationship between the long-term averages of sunshine duration and total cloud cover, an analysis of the monthly mean values of the fraction of the sky C, covered by clouds of all types and the duration of bright sunshine, n, was carried out. The relationship between C and (1−n/N′), where N′ is the maximum possible hours of sunshine, was found to be non-linear. The shape of the regression line connecting the two parameters also shows that ground observations of cloud cover always tend to be overestimates. The differences between such estimates and cloud cover values derived from sunshine duration tend to become zero when skies are either clear or overcast and are a maximum for cloud cover values in the range 0.4–0.7. A cubic regression equation was derived relating C and (1−n/N′) and using this relationship, it has been possible to compute sunshine duration from cloud cover data to an accuracy of about 4–7 per cent and from the cloud derived sunshine data, to compute monthly mean values of global solar radiation to an accuracy of about 6–10 per cent and diffuse solar radiation within an accuracy of about 10–15 per cent.     

On the photovoltaic response of the J-domain and the JA-assembly

Photovoltaic devices based on poly-2′,5′-dioctyl-4,4′′-terphenylenecyanovinylene (J-domain) and 4-aza-4-(4′-(poly-2′,5′-dioctyl-4,4′′-terphenylene-1-cyanovinylene-2-yl)biphen-4-yl)-8,12-dioxa-4,8,12,12c-tetrahydrodibenzo[cd,mn]pyrenium tetrafluoroborate (JA-assembly) were prepared using indiumtinoxide (ITO) as the transparent electrode and aluminium as the second electrode. While the photovoltaic response of the J-domain exhibited low short circuit currents of −0.1 nA cm⁻², the corresponding short circuit current of the JA-assembly was observed to be +10 nA cm⁻². The 100-fold increase in magnitude was related to the known energy transfer from the J-domain to the A-domain in the JA-assembly, and the inversion of the sign of the photovoltaic response that implies that the electrodes have a reversed polarity was explained on the basis of the positions of the energy levels and involves the action of the A-domain as a blocking layer and a light operated charge pump that efficiently transfers electrons to the ITO electrode.