JP2018110252A - Photoelectric conversion device using inclusion fullerene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion device using an inclusion fullerene using a nanocluster.SOLUTION: A photovoltaic device uses an inclusion fullerene including a composite body of supermolecules consisting of an alkali ion inclusion fullerene and an anionic dye. The alkali ion inclusion fullerene is preferentially Li@C. A molecule having the dye-sensitization action is preferentially MTPPS(M is Zn or H). An electrode is preferentially SnO.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photoelectric conversion device using an endohedral fullerene.

    Photoelectrochemical cells (PECs) have been widely studied as next-generation solar cells because of their simple structure. Photoinduced charge separation between the electrode and dye excited state plays an important role in improving PEC performance. In the natural photosynthetic reaction center, effective photoinduced electron transfer occurs, producing a long-life charge-separated (CS) state with high quantum efficiency. Extensive efforts have been made so far to design and synthesize electron donor-acceptor binding molecules to achieve effective photoinduced charge separation for application to PECs. However, the difficulty in synthesizing covalent donor-acceptor molecules has hindered the development of simple photovoltaic devices using such model compounds with photosynthetic reaction centers. Among the many candidates, porphyrins and fullerenes are a suitable combination for constituting PECs. This is because porphyrin has a strong visible absorption band, and fullerene exhibits effective electron mobility such as low relocation energy because the three-dimensional π system is delocalized. Supramolecular approaches aimed at PECs have also been studied, but there have been no reports of supramolecules with strong bonds between neutral porphyrins and fullerenes.

We recently designed and synthesized a simple electron donor-acceptor supramolecular complex composed of lithium ion-encapsulated fullerene (Li ⁺ @C ₆₀ ) and sulfonated mesotetraphenylporphyrin (MTPPS ^4- : M = Zn, H ₂ ). (Non-Patent Document 1). They have strong 1: 1 supramolecular bonds due to cation-anions and π-π interactions (K = −10 ⁵ M ⁻¹ ). The photoexcitation of this supramolecule showed very slow (τ = 0.3 ms) charge recombination in the CS state in benzonitrile (PhCN). Li ⁺ @C ₆₀ has been reported to act as an electron acceptor that is more effective than the original C ₆₀ (Non-patent Document 2). The driving force of photoinduced electron transfer from MTPPS ^4- to triple excited state of Li ⁺ @C ₆₀ is large in positive polarity (ZnTPPS ^4- has -ΔG _ET = 0.98 eV, and H ₂ TPPS ^4- in polar PhCN = 0.67 eV), which is sufficient to produce a CS state even in non-polar environments in nanoclusters.

Chem. Commun., 2012,48, 4314-4316 J.Am.Chem.Soc., 2011,133,15938-15941 J. Phys. Chem. C, 2009, 113, 19694

  However, until now, no specific means has been known about how to construct a battery composed of supramolecular nanoclusters of lithium-encapsulated fullerenes and sulfonated mesotetraphenylporphyrins. There is no such battery.

  An object of this invention is to provide the photoelectric return apparatus using the endohedral fullerene.

  The invention according to claim 1 is a photovoltaic device using an endohedral fullerene comprising a supramolecular complex composed of an alkali ion-encapsulating fullerene and an anionic dye.

  The invention according to claim 2 is the photovoltaic device using the endohedral fullerene according to claim 1, wherein the alkali ion is Li.

The invention according to claim 3, wherein the alkali ion containing fullerene is a photovoltaic device using the endohedral fullerenes as claimed in claim 1 or 2, wherein the Li ⁺ @C _60.

  Photoelectrochemical solar cells composed of supramolecular nanoclusters of lithium-encapsulated fullerene and sulfonated mesotetraphenylporphyrin show significantly higher photoelectrochemical performance compared to a reference system containing only a single component.

_{^{OTE / SnO 2 -MTPPS 4- -Li +}} @C 60) is a schematic image of a photoelectrochemical cell. Is a diagram showing an ultraviolet-visible absorption spectrum of _{^{(MTPPS 4- -Li + @C 60)}} n electrode (red) ^- MTPPS ^4- of PhCN solution (black) and _OTE / SnO ^2. M = (a) Zn, (b) H ₂ ^(A) is a TEM image of _Li + @C 60 -ZnTPPS ^4- and _{^{(b) Li + @C 60 -H}} 2 TPPS 4- nanoclusters. (A) OTE / SnO ₂ — (ZnTPPS ⁴ —Li ⁺ @C ₆₀ ) _n (red), OTE / SnO ₂ — (MTPPS ⁴ —Li ⁺ @C ₆₀ ) _n (blue) and OTE / SnO ₂ − It is a photocurrent action spectrum of (Li ⁺ @C ₆₀ ) _n (black), and (b) a photocurrent action spectrum of OTE / SnO ₂ — (H ₂ TPPS ⁴ − -Li ⁺ @C ₆₀ ) _n . Electrolytic solution: MeCN-PhCN (3.1 v / v) 0.5 M Lil and 0.01 M l ₂ (A) (ZnTPPS ^4- -Li ⁺ @C ₆₀ ) _n transient absorption spectrum in degassed MeCN-PhCN (3.1 v / v) at 30 μs (black) and 200 μs (red) after laser excitation at 550 nm and (b ) Time coordinate diagram at 1035 nm. The inset in (b) is a primary analysis diagram.

Examples will be described below by taking MTPPS ^4- as an example, but the present invention is not limited thereto.

We have here a photovoltaic cell using a nanostructured SnO ₂ optically transmissive electrode (OTE), ie Li ⁺ @C ₆₀ -MTPPS ^4- nanoclusters assembled on (OTE / SnO ₂ ) Report. The photoelectrochemical behavior of the nanostructured SnO ₂ film of supramolecular nanoclusters between Li ⁺ @C ₆₀ and MTPPS ^4- (denoted as OTE / SnO _2- (MTPPS ^4- -Li ⁺ @C ₆₀ ) _n ) is , MTPPS ^4- or Li ⁺ @C ₆₀ cluster single component film (significantly expressed as OTE / SnO ₂ − (MTPPS ⁴⁻ ) _n or OTE / SnO ₂ − (Li ⁺ @C ⁶⁰ ) _n ) High (Figure 1).

Li ⁺ @C ₆₀ -MTPPS ⁴ -Supramolecular solution is in PhCN, Li ⁺ @C ₆₀ PF ₆ (2.5 × 10 ⁻⁴ M) and (Bu ₄ N ⁺ ) ₄ MTPPS ⁴⁻ (2.5 × 10 ⁻⁴ M). 1 mL of PhCN mother liquor was injected into acetonitrile (MeCN) solution (3 mL) to produce a suspension containing supramolecular nanoclusters [(MTPPS ^{4 −} −Li ⁺ @C ₆₀ ) _n ]. (MTPPS ^{4 −} −Li ⁺ @C ₆₀ ) The _n suspension was immersed in a quartz cuvette where two electrodes OTE and OTE / SnO ₂ were installed and held at a distance of 5 mm using a Teflon spacer. Next, when a DC electric field is applied, (MTPPS ^{4 −} −Li ⁺ @C ₆₀ ) _n adheres to the electrode surface from the suspension, and becomes clear by the discoloration of the suspension and the simultaneous coloring of the OTE / SnO ₂ electrode. A strong thin film of OTE / SnO ₂ — (MTPPS ⁴ ——Li ⁺ @C ₆₀ ) _n was formed. For reference purposes, a thin film consisting only of OTE / SnO ₂ or MTPPS was similarly deposited on the electrode surface to form OTE / SnO _2- (Li ⁺ @C ₆₀ ) _n or OTE / SnO _2- (MTPPS) _n .
Steady-state UV-visible absorption spectra were used to follow the adhesion of MTPPS ^{4 −} —Li ⁺ @C ₆₀ supramolecular material to the electrode surface. The UV visible absorption spectrum of OTE / SnO ₂ − (MTPPS ⁴ − −Li ⁺ @C ₆₀ ) _n is illustrated in FIG. 2, but shows a significant spread compared to that in the PhCN solution of MTPPS ⁴⁻ ing. This spread of behavior indicates that porphyrin molecules or supramolecules are aggregated on the OTE / SnO ₂ surface by π stacking. Therefore, MTPPS ^4-- Li ⁺ @C ₆₀ has been successfully deposited on OTE / SnO ₂ . As already reported, the broad absorption band at 725 nm shown in FIG. 2 may be associated with the charge transfer band between the porphyrin surface and the fullerene sphere in the 1: 1 supramolecular complex.

Using TEM, the topography of the OTE / SnO ₂ − (MTPPS ⁴ − -Li ⁺ @C ₆₀ ) _n film as shown in FIG. 3 was measured. The (MTPPS ^4- -Li + @ C ₆₀ ) n membrane consists of a complex cluster of closely packed MTPPS ^4- and Li ⁺ @C ₆₀ with a size of about 80 nm that gives the membrane a nanoporous morphology. Cluster dimensions are also measured by dynamic light scattering (DLS) measurements (see Figure S1 in ESI). As already described in Non-Patent Document 3, the charging of porphyrin and fullerene components in a DC electric field plays an important role in the growth and adhesion process. These coatings are extremely strong and can be washed with an organic solvent to remove all of the coarsely assembled MTPPS ⁴⁻ and Li ⁺ @C ₆₀ nanoassembly.

Photoelectrochemical measurements were performed using a standard two-electrode system consisting of a working electrode and a Pt wire gauge electrode in air-saturated MeCN containing 0.5 M LiI and 0.01 M I ₂ (FIG. 1). A series of photocurrent action spectra was recorded to measure the response immediately before photocurrent generation. Photocurrent values were normalized with respect to incident light energy and intensity, and IPCE (incident photon-photocurrent efficiency) values were calculated using equation (1).
IPCE (%) = 100 × 1240 xi _sc (I _inc xλ) (1)
_{Here, i sc} is the short circuit photocurrent ^(Acm _-2), the _{I inc} incident light intensity ^{(Wcm -2),} λ is the wavelength (nm). The maximum IPCE values for OTE / SnO _2- (Li ⁺ @C ₆₀ ) _n (black spectrum in Fig. 4a) and OTE / SnO _2- (ZnTPPS ^4- ) _n (blue spectrum) are only 5% (425 nm) and 22% (445 nm). Compared to the reference experiment, the IPCE value of OTE / SnO ₂ — (ZnTPPS ⁴ —Li ⁺ @C ₆₀ ) _n is the individual system OTE / SnO ₂ — (ZnTPPS ⁴ —) _n and OTE / SnO ₂ − in the visible region. (Li ⁺ @C ₆₀ ) Much higher than the sum of two individual IPCE values of _n . The maximum IPCE value obtained in these experiments was 77% at 450 nm. The high IPCE value in the Q band region was also observed to be 50% at 570 nm. Such IPCE values are such that photocurrent generation is initiated through photoinduced electron transfer in supramolecules between ZnTPPS ^4- and Li ⁺ @C ₆₀ , and then charge transfer to the OTE / SnO ₂ electrode assembly surface (FIG. 1). . When ZnTPPS ^4- is replaced with H ₂ TPPS ^4- , a significantly lower IPCE value of 7% is probably not bound to Li ⁺ @C ₆₀ , which is observed at 440 nm due to self-aggregation of H ₂ TPPS ^4- (FIG. 4b).

The inventor also measured the power characteristics of the OTE / SnO ₂ — (ZnTPPS ⁴ —Li ⁺ @C ₆₀ ) _n electrode (Figure S2 in ESI). Power conversion efficiency η, equation:
η = FFxI _sc xV _oc / W _in (2)
Calculate using. Here, the filling factor (FF) is defined as FF = [IV] _max / I _sc V _oc , where V _oc is an open circuit photovoltage and I _sc is a short circuit photocurrent. OTE / SnO ₂ — (ZnTPPS ⁴ ——Li ⁺ @C ₆₀ ) _n has a total η value of 2.1% at an input power (W _in ) of 28 mWcm ⁻² , and OTE / SnO ₂ — (ZnTPPS ⁴ — -Li ⁺ @C ₆₀₎ in _{n FF = 0.37, V oc =} 460mV, it is I sc = 3.4mAcm ^-2. Note that this η value is ¹² orders of magnitude larger than the reported simple porphyrin and C ₆₀ composites (˜0.03%). The significantly higher η value demonstrates that strong ordering and effective charge separation within the cluster in ZnTPPS ^4- -Li ⁺ @C ₆₀ ) _n has improved the light energy conversion properties. .

In order to elucidate the mechanism of photocurrent generation, we investigated the formation of the CS state [(ZnTPPS ⁴⁻ ) ^* -Li ⁺ @C ₆₀ ) _n ^* ] by nanosecond laser flash pyrolysis measurement. The time-resolved transient absorption spectrum of (ZnTPPS ^4- -Li ⁺ @C ₆₀ ) _n dispersed in a degassed MeCN-PhCN solution (3: 1 v / v) is shown in FIG. 5a, which shows a broad absorption band around 1035 nm. Is clearly shown. This is characteristic of the formation of Li ⁺ @C ₆₀ radical anions immediately after laser irradiation. Therefore, photoinduced electron transfer occurs from ZnTPPS ⁴⁻ to Li ⁺ @C ₆₀ in the composite cluster, generating the CS state [(ZnTPPS ⁴⁻ ) ^{· +} − (Li ⁺ @C ₆₀ ) _n ^{· −} ]. FIG. 5 b shows an absorption time variation diagram of [(ZnTPPS ⁴⁻ ) ^{· +} − (Li ⁺ @C ₆₀ ) _n ^{· −} ] recorded at 1035 nm. The primary plot (inset of FIG. 5b) corresponds to the reverse electron transfer from Li ⁺ @C ₆₀ ^{• −} to (ZnTPPS ⁴⁻ ) ^+, and the reverse electron transfer rate constant k _BET = 4.6 × 10 ³ s ^−1. give. The lifetime of this CS state is 220 μs, which is long enough to inject electrons from the Li ⁺ @C ₆₀ ^* in the CS state into the SnO ₂ electrode before charge recombination. Such long life CS state, MeCN-PhCN solution containing _{^{(ZnTPPS 4- -Li + @C 60)}} n at 77K: is further detected by EPR under light irradiation (1 1v / v). The EPR signal was observed at g = 2.0020 due to a mixture of porphyrin radical cation (g = 2.002) ¹⁴ and Li ⁺ @C ₆₀ ^* (g = 2.0014) (ESI diagram S3a Reference) ¹⁵ . When ZnTPPS ⁴⁻ was replaced with H ₂ TPPS ⁴⁻ , the transient absorption band due to the CS state was significantly narrower than that of ZnTPPS ⁴⁻ (see ESI in FIG. S4). This is the reason why the IPCE value of OTE / SnO ₂ − (H ₂ TPPS ⁴ —Li ⁺ @C ₆₀ ) _n was low as shown in FIG. 4b.

Based on the above results, initiated from ZnTPPS ^4-) photocurrent generated in the cluster by photoinduced electron transfer to ^Li + _{@C 60,} CS state ^{ZnTPPS 4-) · + - (Li} + @C 60) n · ^- to generate. Li ⁺ @C ₆₀ is reduced (Li ⁺ @C ₆₀ ^{· −} ) (E (Li ⁺ @C ₆₀ / Li ⁺ @C ₆₀ ^{· −} ) = 0.14V vs. SCE), and the electron is SnO ₂ . Injected into the conduction band (0.2v vs. SCE), while ZnTPPS4- oxide is (E (ZnTPPS ⁴⁻ / (ZnTPPS ⁴⁻ ) ⁺ ) = 0.74V vs. SCE) ^{8 in} the electrolyte solution To undergo electron transfer reduction with iodide (I ₃ /I=0.7 V vs. SCE).

In conclusion, the performance of the photoelectrochemical cell can be enhanced by photoinduced electron transfer from ZnTPPS ^4- to Li ⁺ @C ₆₀ in the supramolecular cluster. Thus, using Li ⁺ @C ₆₀ as an electron acceptor in supramolecular clusters with ZnTTPS ^4- opens a new path for the design of high performance solar cells.

Claims (3)

A photovoltaic device using an endohedral fullerene comprising a supramolecular complex composed of an alkali ion-encapsulating fullerene and an anionic dye. The photovoltaic device using the endohedral fullerene according to claim 1, wherein the alkali ion is Li. The alkali ions endohedral photovoltaic device using the endohedral fullerenes as claimed in claim 1 or 2, wherein the Li ⁺ @C _60.

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