Chapter 4 Supramolecular Fluorescence Quenching Effects of H-Donor
4.2.2 Synthesis of Surface-Functionalized Gold Nanoparticles AuSC10 and
The surface-functionalized gold nanoparticles (AuSC10 bearing acid-free surfactants) used in this study were prepared through standard Brust-Schiffrin
mixed with tetraoctylammonium bromide (TOAB) in toluene solution (80 mL, 50 mmol). The two-phase mixture was vigorously stirred until all tetrachloroaurate was transferred into the organic layer, and then dodecanethiol (20 µL) was added to the organic phase. A freshly prepared aqueous solution of sodium borohydride (25 ml, 0.4 mol) was slowly added with vigorous stirring. After further stirring for 3 h, the organic phase was separated, and the standard Brust reaction mixture was evaporated without removing TOAB and dried completely under reduced pressure. The black solid obtained was heat-treated at 165°C at a heating rate of 2°C/min and held at this temperature for 30 min.104 The thermally ‘ripened’ product was dissolved in toluene and washed with methanol to remove excess thiol ligands and TOAB, then AuSC10 nanoparticles with alkyl surfactants were obtained. In the subsequent Murray place exchange reaction,105 AuSC10 nanoparticles (60 mg) were combined with the proper amount of 11-mercaptoundecanoic acid in dichloromethane (3 mg of AuSC10/mL) and reacted for 48 h. After the exchange reaction was completed, the reaction mixture was concentrated using a rotary evaporator. After washing these products with a large amount of ethanol and acetone, no further purifications were conducted on these samples. Then, the acid-functionalized gold nanoparticles (AuSCOOH) with a diameter ca. 5 ~ 6 nm were obtained, and the monolayer compositions of AuSCOOH nanoparticles with both acid and alkyl surfactants were characterized by 1H NMR
featured 79% decanethiol and 21% carboxylic acid thiol functionalities.106 In our studies of nanocomposites, both THF-soluble gold nanoparticles, i.e., alkyl-functionalized gold nanoparticles (AuSC10 bearing acid-free surfactants) and acid-functionalized gold nanoparticles (AuSCOOH bearing acid surfactants), were used.
Figure 4.2 Molecular structures of different lateral methyl- and methoxy-substituted groups of fluorescent side-chain polymers PBT1-PBT3 and PBOT1-PBOT3.
4.2.3 Preparation of Nanocomposites Consisting of Gold Nanoparticles and Polymers
The surface-functionalized gold nanoparticles, AuSCOOH and AuSC10, which contain acid and acid-free surfactants, respectively. Nanocomposites were prepared by mixing solutions (0.5 mg/ml) of surface-functionalized gold nanoparticles
AuSCOOH and AuSC10 in THF. This was then mixed with solutions of two series
O
gold nanoparticles began to assemble into nanocomposites within 2 min. The mixed solutions became visibly turbid, indicating that an aggregation process had occurred.
After 24 h, the solid precipitates were collected and washed extensively with hexane.
The nanocomposites were then dried overnight before being subjected to Transmission Electron Microscopy (TEM) measurements.
4.2.4 Measurements and Characterization
1H NMR spectra were recorded on a Varian unity 300M Hz spectrometer using CDCl3 and DMSO-d6 as solvents. UV-visible absorption spectra were recorded in dilute THF solutions (10-6 M) on a HP G1103A spectrophotometer, and photoluminescence (PL) spectra were obtained on a Hitachi F-4500 spectrophotometer. Fourier transform infrared (FT-IR) spectra were performed on a Nicolet 360 FT-IR spectrometer. Transmission Electron Microscopy (TEM) analyses were performed using a JEOL 2011 electron microscope with an acceleration voltage of 200 keV. The samples were prepared from THF solutions with a concentration of 1 wt%, and the aggregates were precipitated on TEM sample grids (200 Cu mesh/carbon films).
4.3 Results and Discussion
4.3.1 FT-IR Spectroscopic Studies
The formation of hydrogen bonding in two series supramolecular side-chain
polymers PBT1-PBT3 and PBOT1-PBOT3 containing acid-modified gold nanoparticles AuSCOOH was confirmed by FT-IR spectroscopy. As shown in Figure 4.3, IR spectra of PBOT1, AuSCOOH, and H-bonded nanocomposite
PBOT1/AuSCOOH are compared to analyze the hydrogen bonds. In contrast to
acid-modified gold nanoparticles AuSCOOH, the weaker O-H band observed at 2525 and 1920 cm-1 in H-bonded nanocomposite PBOT1/AuSCOOH is indicative of hydrogen bonding between the pyridyl group of PBOT1 and acid-modified gold nanoparticles AuSCOOH in the H-bonded nanocomposite. On the other hand, a C=O stretching vibration appeared at 1695 cm-1 in H-bonded nanocomposite
PBOT1/AuSCOOH, which shows that the carbonyl group was in a less associated
state than that in acid-modified gold nanoparticles AuSCOOH with a weaker C=O stretching vibration appeared at 1660 cm-1. Both results suggest that hydrogen bonds were formed between H-acceptor PBOT1 and H-donor AuSCOOH in the solid state H-bonded nanocomposite PBOT1/AuSCOOH. Some other supramolecular polymers also have the similar consequences of H-bonding formation as the H-bonded polymer complex demonstrated here.17
Figure 4.3 Infrared spectra for AuSCOOH, PBOT1, and H-bonded nanocomposite PBOT1/AuSCOOH at room temperature.
4.3.2 Fluorescence Quenching Effects of Copolymers by Surface-Modified Gold Nanoparticles
In the fluorescence quenching studies, where acid-donor-modified AuSCOOH nanoparticles and non-acid-modified AuSC10 nanoparticles (diameter ca. 5 ~ 6 nm) were doped, the photoluminescence (PL) spectra of two polymers PBOT1 and PBT1 were monitored in the presence of different concentrations of surface-modified gold nanoparticles (Figure 4.4). In Chapter 2, the fluorescence spectra of polymer PBT1 emitted blue light at 440 nm in THF solutions. In comparison with luminescent polymer PBT1, polymer PBOT1 was more red-shifted PL emissions at 440 nm due to the stronger electron donating effect of lateral methoxyl groups, which induce smaller
3000 2500 2000 1500
PBOT1
PBOT/AuSCOOH AuSCOOH
Transmittance
Wavenumber (cm-1)
1695 1660
2525 1920
energy band gaps in chromophores. In Figure 4.4(a) and 4.4(b), H-acceptor polymers
PBOT1 and PBT1 demonstrated dramatic decreases in fluorescence intensities upon
the addition of AuSCOOH nanoparticles (which contain 21% carboxylic acid surfactants). Upon the addition of AuSCOOH, progressive fluorescence quenching effects on polymers PBOT1 and PBT1 (blended with AuSCOOH) were observed by increasing the concentration of AuSCOOH. It is conceivable that the polymer nanocomposites PBOT1-PBT1/AuSCOOH reduced the fluorescence emission intensities by H-bonding complexation of the fluorescent pyridyl units with the acid surfactant on AuSCOOH. In Figure 4.4(a), the polymer PBOT1 was easily H-bonded with the acid H-donor surfactants on AuSCOOH nanoparticles due to the stronger electron donating effect of lateral methoxyl groups, which induce higher affinity on
AuSCOOH. However, as shown in Figure 4.4(b), the titration of methyl-substituted
polymer PBT1 by AuSCOOH nanoparticles displays a similar PL quenching trend as Figure 4.4(a). This suggests that the complexation of methyl-substituted polymer
PBT1 and AuSCOOH nanoparticles has a similar H-bonding interaction as that in the
nanocomposite PBOT1-AuSCOOH. Unlike the methoxyl-substituted polymer
PBOT1, weaker electron donating effect of lateral methyl groups from the
methyl-substituted polymer PBT1 during the H-bonding complexation process in the nanocomposite PBT1-AuSCOOH. Hence, the excitons of methoxyl-substituted
polymer PBOT1 are more easily trapped by the charge-transfer quenchers of
AuSCOOH than those of the methyl-substituted polymer PBT1. As a comparison,
the solutions of polymers PBOT1 and PBT1 were titrated with another nanoparticle counterpart, alkyl-functionalized gold nanoparticles (AuSC10, which bears acid-free surfactants). PL titrations of polymers PBOT1 and PBT1 by AuSC10 nanoparticles (Figure 4.4(c) and 4.4(d)) resulted in similar PL reductions after increasing the concentration of AuSC10 nanoparticles. However, due to less H-bonding interactions of non-acid-modified AuSC10 nanoparticles (containing acid-free surfactants) with polymers PBOT1 and PBT1, AuSC10 nanoparticles have much weaker PL quenching effects on PBOT1 and PBT1 than acid-modified AuSCOOH nanoparticles (Figure 4.4(a) and 4.4(b), respectively). Comparing the insets of Figure 4.4(a)-(d), the fluorescence quenching curves for polymers PBOT1 and PBT1 titrated by AuSCOOH (Figure 4.4(a)-(b)) are totally different from those titrated by AuSC10 (Figure 4.4(c)-(d)). The lower quenching effects observed for PL titrations of
AuSC10 nanoparticles on polymers PBOT1 and PBT1 are owed to the absence of
H-bonding interactions between polymers (PBOT1 and PBT1) and the acid-free surfactants on AuSC10 nanoparticles. In addition, the similar fluorescence quenching curve of AuSCOOH nanoaprticles were observed in the PL spectra of nanocomposites containing various the content of pyridyl groups in the copolymers
PBOT2-PBOT3 and PBT2-PBT3.
The PL quenching behavior follows the Stern-Volmer relation I0/I = 1+KSV[Q],96 where I0 and I are the emission intensities of the fluorescent polymers (PBOT1-PBT3) in the absence and presence of the quencher Q (surface-modified gold nanoparticles), respectively, KSV is the Stern-Volmer quenching constant, and [Q] is the concentration of the quencher. Figure 4.5 demonstrates Stern-Volmer plots of polymers
PBOT1-PBT3 for various concentrations of acid-modified AuSCOOH nanoparticles
and non-acid-modified AuSC10 nanoparticles, which are replotted from the insets of Figure 4.4(a)-(d). The quenching constants (Ksv) of polymers PBOT1 and PBT1 titrated with different nanoparticle quenchers (AuSCOOH and AuSC10) in THF solutions are obtained from the slope of Figure 4.5 and listed in Table 4.1. In comparison with the fluorescence quenching effects of AuSCOOH nanoparticles on polymers polymers PBOT1 and PBT1, the quenching constant (Ksv = 2.50 x 105 M-1) of PBT1 is smaller than that (Ksv = 3.31 x 105 M-1) of PBOT1. This can be explained by that the stronger electron donating effect of lateral methoxyl groups in polymer
PBOT1 which induce higher affinity to complex with AuSCOOH. However,
different to the previous results of polymers PBOT1 and PBT1 titrated with
AuSCOOH, as polymers titrated with AuSC10 nanoparticles, the quenching constant
(Ksv = 2.15 x 104 M-1) of PBOT1 is slightly smaller than that (Ksv = 2.30 x 104 M-1)
of PBT1. It is elucidated that the lateral methoxyl groups in polymer PBOT1 will connect with AuSC10 and competed with the pyridyl terminus of polymer PBOT1.
Due to reduced supramolecular interactions between AuSC10 and polymers PBOT1 and PBT1 in the nanocomposites, both Ksv constants of polymers PBOT1 and PBT1 (2.15 and 2.30 x 104 M-1 without H-bonds) blended with non-acid-modified gold nanoparticles (AuSC10) are much smaller than those (2.50 and 3.31 x 105 M-1 with H-bonds) H-bonded with acid-donor-modified gold nanoparticles (AuSCOOH).
Hence, the H-bonding interactions play an important role in our study of the fluorescence quenching effect. Moreover, it will be more interesting to develop a multicomponent self-assembly process involving fluorescence quenching of pyridyl H-acceptors from polymers PBOT1, PBT1 and acid-donor-modified gold nanoparticles (AuSCOOH). In general, the significant supramolecular interactions between various surface-modified gold nanoparticles and fluorescent polymers can be distinguished by the distinct fluorescence quenching behavior with specific quenching constants (Ksv). In addition, interestingly, we observe that the decreased of pyridyl unit of polymers, Stern-Volmer constants will be decreased exponentially from the experimental information. We demonstrate to follow the relationship between the Stern-Volmer constant (Ksv) and the pyridyl units of polymers. Figure 4.6 gives the plot of Stern-Volmer constant vs pyridyl units of polymers, as suggested by the Ksv =
A(1-e-BX) equation, where A and B are the constants of the experimental equation.
KSV is the Stern-Volmer quenching constant, and X is the percentage of the pyridyl units of polymers. Consequently, it will be easy to predict Stern-Volmer constant in various pyridyl units of polymers from the experimental equation. Due to much smaller Ksv constants of non-acid-modified gold nanoparticles (AuSC10) in polymers without supramolecular interactions, both Ksv constants of polymers PBOT and PBT blended with AuSC10, i.e., AuCS10-PBOT and AuCS10-PBT, are replotted in the inset of Figure 4.6. In order to confirm the fluorescence quenching effects on polymer
PBOT1 by AuSCOOH, UV-visible absorption analyses of polymer nanocomposites,
containing AuSCOOH, were carried out. We would expect the UV-visible absorption spectra to change if the aggregation of fluorescent polymers is induced by the addition of AuSCOOH. In the UV-visible absorption spectra (Figure 4.7(a)), the absorption peaks of polymer PBOT1 (384 and 520 nm in THF solutions) titrated by AuSCOOH do not red shift with increasing Au nanoparticle concentrations (from 0 to 121 μM).
These were the same processing conditions used for the quenching titrations of fluorescent polymer PBOT1 by Au nanoparticles. The reasonably low concentrations (smaller than 121 μM) of AuSCOOH were maintained to avoid the aggregation of fluorescent copolymers and AuSCOOH nanoparticles. Therefore, the aggregation effects on fluorescence quenching can be ignored. The major source of fluorescence
quenching is then attributed to energy transfer between fluorescent polymer (PBOT1) and Au nanoparticles (AuSCOOH). Similarly, as shown in Figure 4.7(b), the absorption peaks of polymer PBT1 (350 and 520 nm in THF solutions) titrated by
AuSC10 do not red shift with increasing Au nanoparticle concentrations (from 0 to 121 μM). These were the same processing conditions used for the quenching titrations of fluorescent polymer PBT1 by non-acid-modified AuSC10 nanoparticles.
Additionally, the similar UV-visible absorption analyses of polymer nanocomposites, containing AuSCOOH and AuSC10, were observed.
Table 4.1 Stern-Volmer Constant (Ksv) for Polymers PBT1-PBOT3 Titrated with Different Nanoparticle Quenchers (AuSCOOH and AuSC10) in THF Solutions
Ksv (M-1)a
PBT1 PBT2 PBT3 PBOT1 PBOT2 PBOT3
AuSCOOH 2.50 x 105 2.17 x 105 1.70 x 105 3.31 x 105 2.67 x 105 2.19 x 105 AuSC10 2.30 x 104 1.96 x 104 1.66 x 104 2.15 x 104 1.82 x 104 1.51 x 104
a The quenching behavior follows the Stern-Volmer relation I0/I = 1+KSV[Q],where I0
and I are the emission intensities of the fluorescent polymer (PBT1-PBOT3) in the absence and presence of the quencher Q (surface-functionalized gold nanoparticles), respectively, KSV is the Stern-Volmer quenching constant, and [Q] is the concentration of the quencher.
(a) (b)
(c) (d)
Figure 4.4 Fluorescence quenching spectra of polymers in THF solutions (a) PBOT1 and (b) PBT1 by varying the concentration of acid-donor-modified gold nanoparticles AuSCOOH (c) PBOT1 and (d) PBT1 by varying the concentration of non-acid-modified gold nanoparticles AuSC10.
400 450 500 550 600
0
400 450 500 550 600 650
0
400 450 500 550 600
0
400 450 500 550 600 650
0
Figure 4.5 Corresponding Stern-Volmer plots of polymers PBT1 (■), PBT2 (●), PBT3 (▲), PBOT1 (▼), PBOT2 (◆), and PBOT3 (★) by increasing the concentration of acid-modified gold nanoparticles AuSCOOH and polymers PBT1 (□), PBT2 (○), PBT3 (△), PBOT1 (▽), PBOT2 (◇), and PBOT3 (☆) by increasing the concentration of non-acid-modified gold nanoparticles AuSC10 in THF solutions, where polymers PBT1-PBOT1 by increasing the concentration of non-acid-modified gold nanoparticles AuSC10 are replotted from inset of Figure.
0 20 40 60 80 100 120
Figure 4.6 Schematic curves showing the dependence of Stern-Volmer constant (Ksv) on pyridyl units’ X mol% of polymers, which follow the experimental equation of Ksv
= A[1-exp(-BX)], where A and B are constants for the exponential curve fittings.
0.0 0.3 0.6 0.9
X mol % (Pyridyl units)
AuSCOOH-PBOT
X mol % (Pyridyl units)
(a)
(b)
Figure 4.7 UV-visible spectra of polymers (a) PBOT1 titrated by varying the concentration of acid-donor-modified gold nanoparticles (AuSCOOH) and (b) PBT1 by varying the concentration of non-acid-modified gold nanoparticles (AuSC10) in THF solutions.
4.3.3 TEM Analyses
To further confirm the modulation of fluorescence quenching effects on two series of polymers PBTO1 and PBT1 by acid-donor-modified gold nanoparticles (AuSCOOH), transmission electron microscopy (TEM) analysis was carried out on polymer nanocomposites containing AuSCOOH nanoparticles. This provides a
300 400 500 600
acid-functionalized gold nanoparticles (AuSCOOH) with a diameter ca. 5 ~ 6 nm were observed in the Figure 4.8(a). Solutions of polymer nanocomposites, consisting of PBTO1 and PBT1 (2 mg/mL) blended with AuSCOOH (0.5 mg/mL) in THF solvent, were drop-cast onto TEM grids. The morphologies of the polymer nanocomposites into structural ensembles were controlled by the supramolecular self-assembly. Regarding H-bonded interactions in the polymers, carboxylic acid units in surface-functionalized gold nanoparticles will be connected with pyridyl groups in the polymers to form H-bonds. The addition of acid-donor-modified gold nanoparticles AuSCOOH to polymers PBTO1 and PBT1 resulted into the formation of extended aggregates. In the case of polymer composites PBOT1/AuSCOOH and
PBT1/AuSCOOH, the morphology of AuSCOOH and polymers were strongly dependent on the H-bonded situations of polymers. In Figure 4.8(b) and 4.8(c), the gold nanoparticles AuSCOOH were homogeneously dispersed in polymers PBOT1 and PBT1 because the H-accepted pyridyl groups in H-bonded structures of polymers in this TEM figure. The self-assembled phenomena of H-bonding between H-donors (from both polymers and nanoparticles) and polymeric H-acceptors are dependent on all existing carboxylic acid groups (H-donors) available for the supramolecular architectures. Hence, AuSCOOH nanoparticles are still homogeneously dispersed in the various pyridyl content copolymers. Besides, the similar aggregation trends of
AuSCOOH nanoaprticles were observed in the TEM images of nanocomposites
containing various the content of pyridyl groups in the copolymers PBOT2-PBOT3 and PBT2-PBT3. The gold nanoparticles AuSCOOH were only partially dispersed in copolymers PBOT2-PBOT3 and PBT2-PBT3 due to the less accepted pyridyl groups in H-bonded structures of copolymers, where the layered CAZ structures of copolymers itself were clearly evidenced in this TEM figure. In order to distinguish the contribution from acid and acid-free surfactants on surface-modified nanoparticles (AuSCOOH and AuSC10, respectively), the polymer PBT1 was blended with non-acid-modified AuSC10 nanoparticles (without H-bonds between polymer PBT1 and AuSC10 nanoparticles). Thus, it is clearly observed in Figure 4.8(d) that non-acid-modified nanoparticles (AuSC10) self-aggregated more extensively. This suggests that no H-bonding interactions occurred between AuSC10 nanoparticles and polymer PBT1. Overall, the TEM morphologies of H-bonded architectures demonstrate the versatility of the self-assembly processes in supramolecular nanocomposites of H-acceptor polymers and H-donor nanoparticles.
(a) (b)
(c) (d)
Figure 4.8 TEM images of (a) acid-modified gold nanoparticles AuSCOOH and blended with polymers (b) PBOT1, (c) PBT1, and (d) alkyl-functionalized gold nanoparticles (AuSC10) blended with polymer PBT1.
4.4 Conclusions
In summary, supramolecular nanocomposites containing two series fluorescent polymers with different pyridyl content, lateral methyl-substituted polymers
PBT1-PBT3 and lateral methoxyl-substituted polymers PBOT1-PBOT3, and donor nanoparticles were developed to display distinct aggregation phenomena in TEM images. H-acceptor polymers PBT1-PBOT3 would not only display highly aggregation but also well dispersion with the proton donor surfactants from
acid-modified gold nanoparticles (AuSCOOH) and lateral methoxyl-substituted polymer PBOT1 affect the fluorescence quenching more effectively, when compared with fluorescence titrations of acid-free-modified gold nanoparticles (AuSC10).
Moreover, in contrast to the lateral methyl-substituted polymer PBT1, lateral methoxyl-substituted polymer PBOT1 more readily captures acid-modified gold nanoparticles (AuSCOOH) in the suparmolecular assembly of nanocomposites. The H-bonding interactions between the pyridyl H-acceptor (from the polymers) and the acid H-donor units (from both nanoparticles and polymers) can explain the similarities in fluorescence quenching effects on both polymers PBOT1 and PBT1.
Moreover, we established the exponential equation to predict Stern-Volmer constant in varous pyridyl units of polymers according to these experimental information.
Various nanocomposites containing two kinds of fluorescent polymer counterparts (methoxyl-substituted polymer PBOT1 and methyl-substituted polymer PBT1) and surface-modified nanoparticles (acid-modified AuSCOOH and acid-free-modified
AuSC10) were developed to display distinct aggregation phenomena in TEM images.
Based on the fluorescence quenching and recovery of gold nanocomposites, further chemosensor and biosensor applications of this study can be developed in the near future.
Chapter 5
Supramolecular Assembly of H-Bonded Side-Chain Polymers Containing Conjugated Pyridyl H-Acceptor Pendants and Various Low-Band-Gap H-Donor Dyes Bearing Cyanoacrylic Acid Groups for Organic Solar Cell Applications
Novel supramolecular side-chain polymers were constructed by complexation of
proton acceptor (H-acceptor) polymers, i.e., side-chain conjugated polymers P1-P2
containing pyridyl pendants, with low-band-gap proton donor (H-donor) dyes S1-S4
(bearing terminal cyanoacrylic acids) in a proper molar ratio. Besides unique
mesomorphic properties confirmed by DSC and XRD results, the H-bonds of
supramolecular side-chain structures formed by pyridyl H-acceptors and
cyanoacrylic acid H-donors were also confirmed by FTIR measurements. H-donor
dyes S1-S4 in solid films exhibited broad absorption peaks located in the range of
471-490 nm with optical band-gaps of 1.99-2.14 eV. Furthermore, H-bonded polymer
complexes P1/S1-P1/S4 and P2/S1-P2/S4 exhibited broad absorption peaks in the
range of 440-462 nm with optical band-gaps of 2.11-2.25 eV. Under 100 mW/cm2 of
AM 1.5 white-light illumination, the bulk heterojunction polymer solar cell (PSC)
devices containing an active layer of H-bonded polymer complexes P1/S1-P1/S4 and
P2/S1-P2/S4 (as electron donors) mixed with [6,6]-phenyl C61 butyric acid methyl
ester (i.e., PCBM, as an electron acceptor) in the weight ratio of 1:1 were
investigated. The PSC device containing H-bonded polymer complex P1/S3 mixed
with PCBM (1:1 w/w) gave the best preliminary result with an overall power
conversion efficiency (PCE) of 0.50%, a short-circuit current of 3.17 mA/cm2, an
open-circuit voltage of 0.47 V, and a fill factor of 34%.
5.1 Introduction
Self-assembled phenomena through molecular recognition between complementary constituents have been explored in various areas, such as the applications of biomaterials, liquid crystalline (LC) materials, and electro-optical materials.65,66,68,83,107 Not only innovative LC properties of novel supramolecules consisting of two counterparts can be generated through intermolecular hetero-hydrogen-bonding interactions, but also particular self-assembly of nano-scaled building blocks using non-covalent interactions (e.g. hydrogen bonding, acid/base proton transfer, and electrostatic forces) may be amplified into macroscopically observable phenomena.50b,84 More recently, direct energy harvesting from sunlight by using photovoltaic cells (PVCs) has increasingly attracted intensified
attention to utilize renewable energy of the nature, especially for the development of organic solar cells.108 Compared with inorganics (such as Si), organic materials (especially polymers) have the benefits to be easily made into devices with light weight, large area, and flexible panels, so different concepts of solar cell architectures have been developed by organics, including blends of polymers109-112 and block copolymers113 with [6,6]-phenyl C61 butyric acid methyl ester (i.e., PCBM, as an electron acceptor). Among the organic solar cell materials investigated so far,
attention to utilize renewable energy of the nature, especially for the development of organic solar cells.108 Compared with inorganics (such as Si), organic materials (especially polymers) have the benefits to be easily made into devices with light weight, large area, and flexible panels, so different concepts of solar cell architectures have been developed by organics, including blends of polymers109-112 and block copolymers113 with [6,6]-phenyl C61 butyric acid methyl ester (i.e., PCBM, as an electron acceptor). Among the organic solar cell materials investigated so far,