Phthalocyanine Blends Improve Bulk Heterojunction Solar Cells

Abstract

A core phthalocyanine platform allows engineering the solubility properties the band gap; shifting the maximum absorption toward the red. A simple method to increase the efficiency of heterojunction solar cells uses a self-organized blend of the phthalocyanine chromophores fabricated by solution processing.Low-cost photovoltaic (PV) devices may derive performance benefits from the light-absorbing properties of phthalocyanine organic dyes because of their high extinction coefficients, stability, and energy band gaps well-matched to the incident solar spectrum. [1][2][3][4] Despite these desirable attributes, use of phthalocyanines in low-cost solar cells is complicated by their poor solubility in organic solvents (necessitating vacuum deposition processing) 2,5,6 and narrow absorption bandwidths at red (Q-band) and ultraviolet (B-band) wavelengths. 7 Bulk heterojunction (BHJ) solar cells with dyes such as phthalocyanine 5,7,8 and polymer blends have been reported. 9,10 There are a several solar cell designs that contain phthalocyanines, especially the zinc and copper complexes, and those that also contain various C 60 derivatives wherein the layers are vapor-deposited in specified layers. [11][12][13] Other soluble dye systems have been incorporated into layered devices, or into BHJ solar cells. 4,[14][15][16] We demonstrate a new blend-type parallel tandem solar cell device architecture with several innovative features. (1) Click-type alkyation chemistry on a single commercially available phthalocyanine platform allows design of a series of robust, chemically compatible dyes with tunable optical band gaps and energy levels. (2) The family of soluble phthalocyanine dyes permits solution-based processing of molecular BHJ solar cells. (3) In these devices, the semiconductor active layer is composed of a blend of three phthalocyanine derivatives having The ca. 70 nm thick blended phthalocyanine active layer provides a disordered tandem device architecture wherein light can be absorbed by materials with successively smaller band gaps and photogenerated charges are collected with a common complementary organic semiconductor. This demonstrates that a hierarchical organization of dyes, wherein the lowest band gap (red) dye is at the surface and higher band gap (blue) dyes are layered or assembled on top, is not a priori necessary to assure vectoral charge migration between the electrodes. 2, 17 A standard, reproducible, solution-processed device architecture is used to illustrate these points. 9,11We achieve both improved phthalocyanine solubility and control over the optical properties using high yield substitution of peripheral fluoro groups on hexadecafluorophthalocyanato zinc (ZnPcF 16 ) by thio-alkanes (CH 3 (CH 2 ) 11 SH) (Scheme 1). 18,19 Because the frontier molecular orbitals (HOMO and LUMO) are primarily delocalized on the ring periphery, substitution of electron withdrawing groups with electron-donating groups affects the orbital energy levels. 5,7 The HOMO is destabilized more than the LUMO, resultin...

A DFT/TDDFT study of porphyrazines and phthalocyanine oxo‐titanium derivatives as potential dyes in solar cells

“…3), because if the LUMO energy is below the TiO 2 conduction band edge, it possibly predict an unfavorable electron injection originating from the sensitizer [44][45][46][47][48]. The complexes 2, 3, and 7 show a HOMO energy very near to HOMO energy of redox couple I À /I 3 À (being this couple used in the regeration of the dye in a DSC [9][10][11]), together with the fact that the complexes show an important absorption in the visible region (vide infra). Besides, it could be important for the charge separation, which may facilitate the electron injection from the dye to the conduction band of semiconductor, and this can be analyzed through the compositons of the HOMO and LUMO, where the HOMO is localized in the donor motif and the LUMO over the acceptor subunit [49][50][51].…”

“…In these cells, the sensitizer has the fundamental role of being responsible for pumping electrons from a lower to a higher energy level, thus making possible the generation of an electric potential difference, which is used to produce electric work. Today, there is a search of finding a sensitizer that achieves effective absorption of sunlight in the red and near-infrared region of the spectra to convert these photons into electricity [7][8][9][10]. Grätzel [11] developed the DSC and, until now, ruthenium(II) bipyridyl complexes have proven to be the most efficient TiO 2 sensitizers, but it is pertinent to mention that ruthenium is a special metal and its sources are limited, so novel inorganic dyes are desirable for highly efficient DSC [12][13][14][15][16].…”

Phase and Texture of Solution-Processed Copper Phthalocyanine Thin Films Investigated by Two-Dimensional Grazing Incidence X-Ray Diffraction

“…Prepared by a careful control of deposition parameters, the vacuum deposited films are usually highly crystalline, with uni-axial orientation along the surface normal [7][8][9]. The application of X-ray diffraction (XRD) analysis is necessary to fully characterize the crystallite phase and orientation information, which is crucial in device fabrication [10]. To accomplish this goal, grazing incidence X-ray diffraction (GIXRD) has been used, since it offers more direct information than, e.g., selected area electron diffraction performed by transmission electron microscopy [11], where the crystal structure and orientation cannot be obtained without the substrate removal.…”

Liquid crystals in photovoltaics: a new generation of organic photovoltaics

“…[1][2][3][4][5][6] During the past decade, organic solar cells have attracted considerable attention owing to their outstanding characteristics, such as potential low-cost fabrication, utilize high throughput, light weight, flexibility and easy processability with efficiency upto 10%. [7][8][9][10][11] Organic PVs (OPVs) has been the subject of enormous scientific interest and therefore has been covered in many reviews, special issues and books. [12][13][14][15][16][17][18][19][20][21][22] Significant attention has been given to overcome technological and materials problems in order to develop these OPV devices, which can perform better than inorganic PV devices.…”

“…These cells are known as heterojunction solar cells. 9 In these heterojunction solar cells, the transportation of the holes and electrons is conducted through organic p-type and n-type semiconductors and the spontaneous charge flow produces electricity. The concept of heterojunction was first introduced using bilayer structures 5 where a layer stacking of donor and acceptor molecules with a planar interface (Figure 1) is realized.…”