WO2012153300A1

WO2012153300A1 - Block copolymer-based solid electrolytes for dye photovoltaic cells, and cells thus obtained

Info

Publication number: WO2012153300A1
Application number: PCT/IB2012/052348
Authority: WO
Inventors: Alessandro Abbotto; Roberto Simonutti; Norberto Manfredi; Alberto Bianchi
Original assignee: Universita' Degli Studi Di Milano-Bicocca
Priority date: 2011-05-12
Filing date: 2012-05-11
Publication date: 2012-11-15
Also published as: ITMI20110833A1

Abstract

The subject of the present invention is novel block copolymer-based solid electrolytes for the construction of solid state organic or organometallic dye photovoltaic cells, or dye sensitised solar cells - DSC. The block copolymers are based on poly(oxyethylene), PEO, and characterised by the general formula (I) (A_n-PEOm-A_n), or (II) (R₁ PEO_m-A_n).

Description

BLOCK COPOLYMER-BASED SOLID ELECTROLYTES FOR DYE PHOTOVOLTAIC CELLS, AND CELLS THUS OBTAINED

Field of the invention

The subject of the present invention is novel block copolymer-based solid electrolytes for the construction of solid state organic or organometallic dye photovoltaic cells. State of the art

One of the most important priorities for modern society is to find sources of low-cost energy, which have low environmental impact and are available in abundance. In recent decades, the attention of the scientific and technology communities has been focussed on sources of renewable energy. Thanks to the inexhaustible energy source that is the sun, photovoltaic energy appears to be one of the most promising renewable energy sources (Jacoby, M. Chem. Eng. News 2007, 85, 16-22; Kleiner, K. Nature 2009, 459, 740). The high cost of silicon cells has called for the development of novel thin-film photovoltaic technologies. In particular, dye sensitized solar cells (DSC), based on the use of a completely or partially organic matrix photosensitiser, show promising development prospects in terms of the efficiency/cost compromise (Graetzel, M. Acc. Chem. Res. 2009, 42, 1 788-1798). In a DSC device, a photosensitiser compound, also known as the dye, absorbs sunlight, creating an electron-hole pair at the interface with a semiconductor oxide (preferably titanium dioxide) and an electrolyte (preferably the iodine/iodide redox couple). The separated charges are then transported to the electrodes with the creation of an electric current (O'Regan, B.; Graetzel, M. Nature 1991 , 353, 737-740; Graetzel, M. Nature 2001 , 414, 338-344; Hamann, T.W.; Jensen, R.A.; Martinson, A.B.F.; Ryswyk, H.V.; Hupp, J.T. Energy Environ. Sci. 2008, 1, 66-78; Luo, Y. ; Li, D.; Meng, Q. Adv. Mater. 2009, 21, 4647-4651 ). Currently, the highest conversion efficiencies are reported for complexes of Ruthenium (II) with 2,2'-bipyridyl (bpy) ligands. The most efficient photosensitiser in this series is the complex c/s-dithiocyanate bis(2,2'-bipiridyl-4,4'- dicarboxylate)ruthenium(ll), also known as N719 (Nazeeruddin, M.K.; DeAngelis, F.; Fantacci, S.; Selloni, A.; Viscardi, G.; Liska, P. ; Ito, S.; Takeru, B.; Gratzel, M. J. Am. Chem. Soc. 2005, 127, 16835-16847). In its most common and widely developed embodiment, the DSC device contains a liquid electrolyte based on a solution (in organic solvents such as acetonitrile and valeronitrile) containing iodine , organic (e.g. imidazolium) or inorganic (e.g. Lil) ion iodides and other components (Ito, S.; Murakami, T.N.; Comte, P.; Liska, P.; Gratzel, C; Nazeeruddin, M.K.; Gratzel, M. Thin Solid Films 2008, 516, 4613-461 9). Despite making it possible to achieve highest energy conversion efficiencies, thanks to optimised interaction between the liquid electrolyte and the dye-containing titanium dioxide film, this composition is not suitable for the industrial development of DSC cells. In particular, in order to make DSC devices suitable for external use it is important to consider the duration and long-term stability of DSC cells and modules as well as the use of environmentally compatible materials.

This cannot be achieved with a liquid electrolyte for the following main reasons:

- the organic solvents are toxic and, through evaporation, pollute the atmosphere and destroy the function of the electrolyte;

- the liquid electrolyte can leak from the device, especially in all those applications where vertical devices are used (e.g. in building integration: covering of building surfaces);

- the cell closure (sealing) is inefficient;

- the thermal stability is insufficient;

- the medium to long-term stability is limited due to the liquid electrolyte being incompatible with the metal components of the device, since the liquid electrolyte is corrosive and, through leakage, destroys the metal components.

In order to remedy these drawbacks, solid and semi-solid electrolytes have been studied in recent years as an alternative to liquid electrolytes (Snaith, H. J.; Schmidt- ende, L. Adv. Mater. 2007, 19, 3187-3200; Snaith, H.J.; Moule, A.J.; Klein, C; Meerholz, K.; Friend, R.H.; Gratzel, M. Nano Lett. 2007, 7, 3372-3376; Yum, J.-H. ; Chen, P.; Gratzel, M.; Nazeeruddin, M.K. ChemSusChem 2008, 1, 699-707; Yanagida, S. ; Yu, Y.; Manseki, K. Acc. Chem. Res. 2009, 42, 1827-1 838; Mishra, A.; Fischer, M.; Bauerle, P. Angew. Chem. Int. Ed. 2009, 48, 2474-2499). Among the various solutions proposed are the use of ionic liquids, hole transporter polymeric semiconductors, molecular hole transporter (2,2',7,7'-tetrakis-(N,N-di-p- methoxyphenylamine)-9,9'-spirobifluorene or spiro-MeOTAD). In all such cases, the energy conversion efficiency is poor due to the low mobility of the charge transporters in the electrolyte and the imperfect contact between the electrolyte and the photosensitiser-decorated titanium dioxide nanoparticles. On the other hand, the use of polymer gels may improve these contacts and in perspective lead to higher efficiencies (Shi, J.; Peng, S.; Pei, J.; Liang, Y.; Cheng, F.; Chen, J. ACS Applied Materials & Interfaces 2009, 1, 944-950).

Ion conductivity in polymers results from the simultaneous presence of two properties: the ability to solvate cations by means of donor atoms present in the structure; the high segmental mobility of the major chain. Polyoxyethylene (PEO) based electrolytes possess both these properties and have thus been extensively studied for use in lithium batteries and more recently also in DSCs. The main problem with the use of PEO, particularly with high molecular weights, is its tendency to crystallise. Indeed, ion conductivity is blocked in the compact packing of the crystalline phase and the overall conductivity of the electrolyte drops drastically. Crystallinity is reduced with reducing molecular weight, but with a parallel deterioration in mechanical properties. Two main pathways have been followed with the aim of overcoming this problem: a) disperse the PEO in another polymer with better physico-chemical properties, obtaining a polymer "blend", so as to impede its crystallisation and in any case obtain good mechanical properties (Yang, Y.; Zhou, C.H.; Xu, S.; Hu, H.; Chen, B.L.; Zhang, J.; Wu, S.J. J. Power Sources 2009, 185, 1492-1498; Lee, J .Y.; Bhattacharya, B.; Kim, D.W.; Park, J.K. J. Phys. Chem. C 2008, 1 12, 12576-1 2582); b) use statistical copolymers containing other monomer units in addition to the oxyethylene units of the PEO (Nogueira, A.F.; Durrant, J.R.; De Paoli, M. A. Adv. Mater. 2001 , 13, 826-830). These two approaches, even if they have made it possible to obtain significant conversion efficiencies (De Paoli and co-workers report a sunlight energy to electrical energy conversion efficiency of 1 .6% with illumination of 1 sun for the poly(epichlorohydrin-co-ethylene oxide system - Epichlomer-16, Daiso Co. Ltd Osaka, Japan), show certain critical aspects. With regard to statistical copolymers, their poor modulability must be reminded. Indeed, the composition of a statistical copolymer is determined by the reactivity ratios r between the two monomers during copolymerisation, and it is thus most often impossible to vary the composition of the copolymer in a controlled manner, thus in fact limiting the possibility of fine tuning the properties of the copolymer ("Principles of Polymerization" G. Odian, Wiley 2004). Also, in a statistical copolymer, the random distribution of the comonomer, not participating in the conduction phenomenon, can create obstacles to conduction itself. On the other hand, the use of polymer mixtures ("blends") poses a problem with the long-term duration of the cells: indeed, the polymers in the mixture have a tendency to segregate for thermodynamic reasons, quantifiable in the polymer-polymer interaction parameter χ.

An alternative approach is based on the use of block copolymers. Block copolymers are polymers formed by repeating blocks of chemically different monomer units bonded together covalently and thus possess different properties compared to mixtures of the corresponding homopolymers. The chemical distinction between the different chains leads to ordered mesophases, and hence separation between microphases (Li M., Ober C.K., Materials Today 2006, 9, 30-39, Bates F.S., Fredrickson G.H., Physics Today 1999, 52, 32-38). In the case of block copolymers of type AB, wherein the two blocks are immiscible, there is autoassembly into various ordered microstructures. At high temperatures there is a disordered phase (DIS) wherein blocks A and B mix homogeneously; with reducing temperature (i.e. with increasing Flory-Huggins equation parameter χΝ), they separate at the microscopic level forming domains rich in A or domains rich in B separated by a vast quantity of internal interface. These domains can assume various geometries, principally as a function of the mean spontaneous curvature of the internal interface, which is produced by a lack of correspondence between the entropy contribution to the stretching energy between blocks A and B. The classic structures are lamellar (L), hexagonal with hexagonally packed cylinders (H) and spheres packed within a body- centered cubic lattice (bcc). In the case of copolymers of three or more blocks, there can be various possibilities for each of these three basic structures in addition to linear combinations. By way of example, in the case of an ABC triblock, there can be cylinders of A dispersed in a lamellar matrix of BC, or cylinders of B dispersed in a lamellar matrix of AC or finally cylinders of C dispersed in a lamellar matrix of AB. Each of the morphologies indicated has different physico-chemical and mechanical properties.

On the basis of this complex and rich morphological variety, block copolymers represent a versatile class of templates for nanoarchitecture construction (Kim, H.-C;

Park, S.-M.; Hinsberg, W. D. Chem. Rev. 2010, 110, 146-177).

In particular, the hexagonal structure is particularly adapted to an ion conduction process, particularly when all cylinders are oriented with the main axis perpendicular to the surface of the electrodes; furthermore, the cylindrical geometry hampers crystallinity.

The development of "pseudo living" radical polymerisation techniques, such as ATRP (Atomic Transfer Radical Polymerization, Wang, J.-S. and Matyjaszewski, K. J. Am. Chem. Soc. 1995, 7 /7, 5614-5615) or RAFT (Reversible Addition and Fragmentation Transfer, Moad, G.; Rizzardo, E. and Thang, S.H. Polymer 2008, 49, 1 079-1 131 ) has made it possible to synthesise a large number of block copolymers. The RAFT polymerisation processes are a recent technology and arise from the need to be able to combine the advantages of radical polymerisation with those of living polymerisation (preferably anionic), while minimising the problems associated with them. On the other hand, despite having the advantage of being very simple to achieve, radical polymerisations are not adapted to processes where it is essential to have high selectivity and uniformity of the products obtained, since they are poorly controllable and provide polymers of highly variable molecular weight. In addition, as already mentioned, anionic polymerisation processes have the disadvantage of being usable only with a limited number of monomers and require the use of highly expensive catalysts and very severe conditions.

On the other hand, RAFT polymerisation is distinguished by its versatility in that it may be applied to a vast range of monomers and different reaction conditions, guaranteeing polymers with good average molecular weight control and molecular weight distribution. Furthermore, the polymerisation reaction can take place in solution, in emulsion and in mass using common peroxide or nitrogen-based initiators, without there being any particular limitations regarding solvents or reaction temperature.

The mechanism of this type of polymerisation is based on a transfer agent preferably formed from a dithioester where the carbonyl is substituted with an amino, ester or thiol group, and where the ex-thiol sulphur is substituted with a good leaving group.

Z = aryl, alkyl, NR'₂, OR', SR'

R = Homolytic leaving group

Group Z may be: phenyl, para substituted phenyl (4-methoxyphenyl), methyl, ethyl thiododecyl, thiooctadecyl. Group R may be: CH₂CH2CO₂H, (CH₃)₂CCOOH, 2-cyano- 2-propyl, 4-cyanopentanoic acid. These transfer agents are commonly known as "chain transfer agents" (CTA).

Summary of the invention

According to the present invention it has now been found that solid or semisolid electrolytes, effective for the manufacture of solid DSC devices not containing liquid electrolytes, can be made from block copolymers as the major component characterised by the following general formula:

(I) (A_n-PEO_m-An)

wherein A is a monomer selected from: styrene, alkylstyrene, halogen styrene, alkyl methacrylate, alkyl acrylate, aminoalkyi methacrylate, aminoalkyi acrylate, N-alkyl aminoalkyi methacrylate, N-alkyl aminoalkyi acrylate, acrylamide and Ν,Ν-dialkyl and N-monoalkyl substituted acrylamides, acrylonitrile, alkoxy acrylate, alkoxyalkyl methacrylate, hydroxyalkyl acrylate, hydroxyalkyl methacrylate alkylthio; said alkyl residues having 1 -20 carbon atoms and being linear or branched; '

PEO is poly(oxyethylene); Ri= methyl, ethyl, butyl, tert-butyl; m is comprised between 10 and 5000, preferably between 100 and 200; n is comprised between 10 and 10000, preferably between 50 and 500. PEO is preferably polyoxyethylene with molecular weight comprised between 500 and 250000 Daltons, more preferably between 4000 and 10000 Daltons.

Blocks A_n are characterised by low polydispersity indices D, such as D=1 .05-1 .15. The subject of the present invention is also non-liquid electrolytes which, besides containing one or more block copolymers characterised by general formulas (I) and (II) above as the major components, also contain chemical species, such as redox pairs, capable of transporting negative and positive charges between the counter electrode and the other components of the cell, in particular with a photosensitiser absorbed on the surface of titanium dioxide. These chemical species are selected from iodine or triiodide and the iodides of inorganic cations, for example Lil or Nal, and organic cations, for example alkylimidazolium salts. The electrolyte may also contain the additives necessary for improved function of the device, such as for example tert-butylpyridine and guanidinium thiocyanate.

The present invention also concerns reference photoelectrical devices (see Gratzel, M. Nature 2001 , 414, 338-344), photoelectric conversion devices, photovoltaic devices and/or solar cells (Ito, S.; Nazeeruddin, M. K.;Liska, P.; Comte, P:, Charvet, R.; Pechy, P.; Jirousek, M.; Kay, A.; Zakeeruddin, S.M.; Graetzel, . Prog. Photovolt: Res. Appl., 2006, 14, 589) that use a compound containing the block copolymers according to the present invention as electrolyte.

A solar cell adapted to contain the polymer electrolytes according to the invention consists of a photoelectric conversion device from light energy, preferably sun light, to electrical energy, comprising the following components: a) a light absorbing component (photosensitiser); b) a semiconductor material, preferably titanium dioxide, onto which the light absorbing component is adsorbed; c) a charge transporting component (electrolyte) in accordance with the polymer compounds of the present invention; d) a transparent working electrode; e) a counter-electrode. The semiconductor material is preferably present in the form of mono- or multi-layer mesoscopic film containing nanoparticles of dimensions ranging from a few to several tens or hundreds of nanometres and may be either transparent or opaque or, in multilayer form, contain both transparent or opaque films, and have a thickness comprised between 5 and 100 μιη.

Brief description of the figures

The characteristics and advantages of the present invention are illustrated in greater detail with reference to the attached figures.

Figure 1 shows a layout of a solar cell containing a solid electrolyte according to the invention.

Figure 2 shows the current/voltage density curves relative to the characterisation under solar simulator illumination of the DSC cell containing a solid electrolyte PSig₆- PEOi₃₆-PSi₉₆ according to general formula (I) of the invention, wherein PS _^polystyrene.

Detailed description of the invention

The invention is now described with reference to certain preferred compounds belonging to general formula (I) and (II), according to examples which are purely illustrative and non-limiting of the scope of the invention.

EXAMPLE 1

Preparation of the macrotransfer agent

Method 1

PEO 6000 was anhydrified by dispersion in toluene and then by distilling the toluene/water azeotrope; the transfer agent was dried under mechanical vacuum for 2 h. The dichloromethane used as a solvent was anhydrified by distillation. 2 g of PEO 6000 and 270 mg of transfer agent were added to a 100 ml Schlenk tube and there dissolved in 5 ml of dichloromethane with magnetic stirring. 4-(dimethylamino)pyridine (DMAP), 40 mg, was added and the mixture degassed in a stream of nitrogen, again with constant stirring. 160 mg of dicyclohexylcarbodiimide (DCC) dissolved in 1 ml di dichloromethane was then slowly added dropwise. The reaction was conducted at 0°C in an ice/water bath for 12 hours and at 25 °C for 48 hours with magnetic stirring. The solution was filtered to remove the urea formed, and precipitated three times in diethyl ether. The macrotransfer agent was dried under mechanical vacuum for 24 hours at 35 °C. 1 .18 g of CTA-PE0_{1 3}6-CTA, wherein CTA = 2-(dodecylthiocarbonothyoylthio)-2-methylpropionic acid, was obtained as a yellowish solid with a yield of 52%.

Method 2

Using a syringe, 0.3 g of oxalic chloride and 0.7 g of S-1 -Dodecyl-S'-(a,a'-dimethyl- a"-acetic acid) trithiocarbonate dissolved in suitably distilled and anhydrified dichloromethane (transfer agent to oxalic chloride ratio 1 :1 .1 ) were added to a 100 ml Schlenk tube. The solution was stirred using a magnetic stirrer under an atmosphere of nitrogen. The two compounds combine to form an unstable intermediate which has a tendency to break down immediately, forming carbon dioxide, carbon monoxide and the chloride of the acid. At the end of the reaction, which occurs after approx. five hours and is indicated by cessation of gas formation, the solvent was eliminated by applying a mechanical vacuum to the tube, and the product was then dried. The sample was redissolved in 20 ml of anhydrous dichloromethane and reacted, transferred using a cannula under nitrogen to a reaction flask containing 5 g of PEO 6000 dissolved in 20 ml of anhydrous CH₂CI₂, and 0.17 g of distilled and anhydrous triethylamine was added to the reaction mixture. The reaction continues under an atmosphere of nitrogen, with magnetic stirring. After 18 hours the mixture is filtered and precipitated three times in diethyl ether. The esterification reaction between PEO and the acid chloride leads to the formation of the desired compound CTA-PEOi₃₆- CTA. The sample is purified using a kumagawa with hexane for 24 hours and dried under a mechanical vacuum, 5.1 g, yield 89%. Synthesis of the block copolymer

Method 1

For the purpose of conducting the polymerisation of the second block with styrene, 86 mg of (CTA-PEOi₃₆-CTA) are dried in a 10 ml Schlenk tube under a mechanical vacuum, then 3 ml of styrene, distilled under reduced pressure prior to use (styrene/PEO ratio = 100) and 3 ml of 1 ,4-dioxane are added. The solution thus obtained is degassed (freeze-pump-thaw) three times. The polymerisation was conducted for 22 hours at 1 10 °C in an oil bath with magnetic stirring and in a stream of nitrogen. The solution was precipitated three times in diethyl ether. 0.3 g of PS₈o- PEOi₃6-PS₈o was obtained, corresponding to a conversion of 10%. The length of the styrene blocks was determined by proton NMR spectroscopy in solution. Method 2

The polymerisation with styrene was performed using the same procedure, varying the ratio between monomer and transfer agent. In particular, using a ratio of 250 to 1 and conducting the reaction for 48 h, PSi96-PEOi₃₆-PSi₉₆ was obtained with a polydispersity of 1 .12.

The block copolymer-based solid electrolytes according to the invention show photoelectric conversion properties when inserted, together with the other components, in a photoelectric conversion device, in a solar cell or in a photovoltaic device.

In this regard, again purely by way of example, experimental data are described relating to the evaluation of the photoelectric conversion properties of the compounds according to the invention.

The following parameters are introduced:

Jsc = maximum obtainable photocurrent density, measured under short-circuit conditions (mA/cm²);

Voc = maximum obtainable potential, measured under open circuit conditions (V) ; FF = fill factor, which is obtained from the ratio between Jm_PxV_mp and Jsc V_0C, where J_mp is the photocurrent density at the point of maximum power and V_mp is the cell potential at the point of maximum power;

η = light energy - electrical energy conversion efficiency (%), measured under standard AM 1.5 illumination conditions, corresponding to 100 mW/cm² or 1000

W/m², obtained by applying the following equation:

η = Jsc [mA/cm²] x V_oc [V] x FF / 1₀ [mWcm^"2]

where l₀ = 100 mW/cm² or 1000 W/m² under AM 1 .5 conditions.

EXAMPLE 2

This example refers to the characterisation of the photoelectric conversion properties of the solid electrolyte based on the copolymer PS196-PEO136-PS-196 when included in a photoelectric conversion device (DSC cell), the general layout of which is shown in Figure 1 .

The scope of this characterisation is only to demonstrate the photoelectric conversion properties of the novel compounds and is not aimed at obtaining photoelectric conversion efficiency values optimised and measured under the best conditions achievable.

The cell shown schematically in Figure 1 consists of two substrates 1 , containing a conductor layer, of which at least one is transparent (TCO); a semiconductor material 2, for example titanium dioxide, onto which is adsorbed a compound with light absorber function; a charge carrier component 3 based on the block copolymer according to the present invention; and a counter electrode 4, for example TCO coated with platinum.

The DSC cell is prepared as follows. A TCO=FTO (fluorine doped tin oxide, Solaronix TC0022-7) based conductor substrate is thoroughly cleaned according to the following procedure: detergent solution in an ultrasonic bath for 30 minutes, water, ethanol. The FTO substrate is then treated with an aqueous solution of 0.04 M TiCI₄ for 30 minutes at 70 °C and then re-washed with water and ethanol.

A first layer of transparent titanium dioxide consisting of nanoparticles of mean size 15-20 nm (Solaronix T20/SP) is then deposited manually (squeegee technique), followed by heat treatment at 125 °C for 10 minutes. The second layer of opaque titanium dioxide (CCIC PST-400C) is then deposited using the same technique, so that the overall thickness, measured by profilometer following sintering, is comprised between 12 and 15 μιη. The substrate with the titanium dioxide is then subjected to the following heat treatment: 325 °C for 10 minutes, 450 °C for 15 minutes, 500 °C for 15 minutes. The area covered by titanium dioxide ("active area") is 0.40 cm². After heat treatment, the FTO glass with the titanium dioxide film is once more treated with an aqueous solution of 0.04 M TiCI₄ for 30 minutes at 70 °C, washed with water and ethanol and then treated at 500 °C for 30 minutes. On completion of the heat treatment, after being left to cool to 80 °C,^; the substrate is immersed in a solution of the photosensitiser (for example, N7 9) (concentration = 10^" M) in acetonitrile and tert-butyl alcohol (1 :1 ) containing chenodeoxycholic acid as co-adsorbent (at the same concentration) for 20 hours.

The cell is then covered with a counter electrode prepared follows. An FTO glass is washed thoroughly with water, a solution of 0.1 M HCI in ethanol and acetone (with ultrasound treatment) and then heated for 15 minutes at 400 °C in order to remove all traces of contaminants. A drop of a solution of H₂PtCI₆ in ethanol (1 g/L of platinum) is then deposited and the treatment repeated for 15 minutes at 400 °C.

A solution of PS-i9₆-PEOi₃₆-PS₁₉6 (5 mg in 0.5 ml dichloromethane) is deposited by cast film on the counter electrode thus prepared and the solvent allowed to evaporate, thus giving a homogeneous film. The I /l₃ based electrolyte (Dyesol EL- HPE) (50 μΐ_) is then deposited at left to absorb for 12 hours.

The substrate containing the photosensitiser-treated titanium dioxide film is then closed with the counter electrode containing the Pt, prepared as previously described, sealing the perimeter with a layer of thermoplastic sealer (Dyesol TPS 065093-50G). The photovoltaic properties of the DSC cell thus obtained are characterised using an Oriel 81 160 solar simulator with a 300 W Xenon lamp under standard AM 1 .5 illumination conditions. The results are reported in the following tab e together with the measurements obtained under the same conditions using the conventional I I3 based liquid electrolyte (Dyesol EL-HPE).

Figure 2 shows the current-voltage density curves for the DSC cell containing the compound PS₁₉₆-PE0₁₃6-PSi₉₆.

Claims

1 . Block copolymer characterized by the general formula

(I) (A_n-PEO_m-A_n)

or (II) (Pu PEC An)

wherein A is a monomer selected from: styrene, alkylstyrene, halogen styrene, alkyl methacrylate, alkyl acrylate, aminoalkyl methacrylate, aminoalkyl acrylate, N-alkyl aminoalkyl methacrylate, N-alkyl aminoalkyl acrylate, acrylamide and Ν,Ν-dialkyl and N-monoalkyl substituted acrylamides, acrylonitrile, alkoxy acrylate, alkoxy alkyl methacrylate, hydroxyalkyl acrylate, hydroxyalkyl methacrylate alkylthio; said alkyl residues having 1 -20 carbon atoms and being linear or branched;

PEO is poly(oxyethylene); Ri= methyl, ethyl, butyl, tert-butyl; m is comprised between 10 and 5000, preferably between 100 and 200; n is comprised between 10 and 10000, preferably between 50 and 500.

2. Block copolymer according to claim 1 , characterized in that PEO has molecular weight comprised between 500 and 250000 Daltons.

3. Block copolymer according to claim 2, characterized in that PEO has molecular weight comprised between 4000 and 10000 Daltons.

4. Block copolymer according to claim 1 , characterized by the formula PS-|₉₆- PEO-I 36-PS-I96, wherein PS is polystyrene.

5. Block copolymer according to claim 1 , characterized by the formula PSso- PEOi₃₆-PS8o, wherein PS is polystyrene.

6. Electrolyte in solid or semi-solid form for a photoelectric energy conversion device, containing at least a block copolymer according to Claim 1 .

7. Electrolyte in solid or semi-solid form, containing at least a block copolymer according to claim 1 , in mixture with PEO having molecular weight comprised between 500 and 10000.

8. Electrolyte in solid or semi-solid form according to claims 6 and 7, comprising chemical species able to carry positive or negative charges, also by means of oxido-reductive reactions.

9. Electrolyte according to claim 8, wherein said chemical species are selected from iodine and iodides of inorganic or organic cations.

10. Electrolyte according to claims 6, 7, 8 comprising chemical additives.

1 . Photoelectric energy conversion device using an electrolyte according to any one of the preceding claims.

12. Photovoltaic cell according to claim 1 1 .