Phenoxy-(Chloro) n -Boron Subnaphthalocyanines: Alloyed Mixture, Electron-Accepting Functionality, and Enhanced Solubility for Bulk Heterojunction Organic Photovoltaics.

The first set of phenoxy BsubNc compounds, PhO-Cl n BsubNc and F5-Cl n BsubNc, was synthesized through an axial displacement reaction of Cl-Cl n BsubNc with phenol and pentafluorophenol (respectively). Like their precursor, the products were found to be an alloyed mixture of phenoxylated Cl n BsubNcs with random positioning in the solid state yet consistent frequency of bay position chlorination. The average bay position chlorine occupancy was determined to be 0.99 through single crystal diffraction of PhO-Cl n BsubNc. Although the phenoxylation of Cl-Cl n BsubNc did not influence the chromophore photophysical properties, the electrochemical behavior was found to be more stable. Phenoxylation yielded differences in organic photovoltaic (OPV) device metrics. Specifically, a significant increase in open circuit voltage (V OC) was observed, ultimately exceeding 1.0 V when phenoxylated Cl n BsubNcs were paired with alpha-sexithiophene (α-6T) in planar heterojunction OPVs. Phenoxylation enabled the first example of BsubNcs incorporated into polymer-based bulk heterojunction (BHJ) OPVs through enhanced solubility. Phenoxylated Cl n BsubNcs, when paired with poly-3-hexylthiophene, also showed high V OC in BHJ OPVs with broad spectral absorption up to 760 nm. In the BHJ case, simple phenoxy was shown to be a better axial substituent compared to pentafluorophenoxy. This study represents the first example of using Cl n BsubNcs with nonchlorine axial substituents in OPVs and demonstrates that phenoxylation has a significant impact on device metrics while enhancing solubility to enable incorporation of Cl n BsubNcs into BHJ OPVs.

Characterization of µ-oxo-(BsubPc)2 in Multiple Organic Photovoltaic Device Architectures: Comparing against and Combining with Cl-BsubPc.

We demonstrate the first application of a unique boron subphthalocyanine (BsubPc) derivative, the oxygen bridged dimer µ-oxo-(BsubPc)2, as a multifunctional material within planar heterojunction organic photovoltaic (OPV) devices. We first explored the pairing of µ-oxo-(BsubPc)2 with well-known electron accepting and electron donating materials to explore its basic functionality. These preliminary device structures and metrics indicated that µ-oxo-(BsubPc)2 is best applied as an electron donating material when used in simple bilayer structures, as it yielded comparable OPV device efficiencies to that of the more well-established and highly optimized chloro-boron subphthalocyanine (Cl-BsubPc) OPV device structures. Thereafter we established that the HOMO/LUMO energy levels of µ-oxo-(BsubPc)2 are well-placed to apply it as a bifunctional donor/acceptor interlayer material in both energy and charge cascade OPV device architectures. Within this context, we found that µ-oxo-(BsubPc)2 was particularly effective in a charge cascade device as an interlayer between Cl-BsubPc and C70. We finally found evidence of an alloying-like effect for devices with mixed electron donor layers of (Cl-BsubPc) and µ-oxo-(BsubPc)2, achieved through co-deposition. The overarching conclusion is therefore that µ-oxo-(BsubPc)2 has the ability to improve the performance of Cl-BsubPc OPV devices and is a multifunctional material worthy of further study.

Evaluating thiophene electron-donor layers for the rapid assessment of boron subphthalocyanines as electron acceptors in organic photovoltaics: solution or vacuum deposition?

In this study, we consider the choice of a standard electron-donating material to be paired with boron subphthalocyanines (BsubPcs) to rapidly assess the viability of new BsubPc derivatives as electron-accepting materials within organic photovoltaic devices (OPVs). Specifically, we evaluate the effectiveness of solution-cast poly(3-hexylthiophene-2,5-diyl) (P3HT) as an electron donor paired with BsubPc derivatives relative to vacuum-deposited sexithiophene (α-6T). By using fullerene (C60 ), boron subphthalocyanine chloride (Cl-BsubPc), and hexachloro boron subphthalocyanine chloride (Cl-Cl6 BsubPc) as electron acceptors, we find that devices made with α-6T outperform those with P3HT. However, the two thiophene-based materials show the same performance trends. Given the preservation of these trends, we can recommend either option for assessing the potential of new BsubPc derivatives; P3HT as a solution-cast electron-donor layer or α-6T as a vacuum-deposited alternative.

Process for the synthesis of symmetric and unsymmetric oxygen bridged dimers of boron subphthalocyanines (µ-oxo-(BsubPc)2s).

A process for the gram scale synthesis of the oxygen bridged dimer of boron subphthalocyanine, µ-oxo-(BsubPc)2, has been developed. During the development it was found that a wide range of reaction pathways under diverse conditions lead to µ-oxo-(BsubPc)2 formation. However, obtaining µ-oxo-(BsubPc)2 as the main reaction product in appreciable yields and its subsequent isolation were extremely challenging. The best balance of purity, yield and conversion was achieved with a time controlled reaction of an equimolar reaction of HO-BsubPc with Br-BsubPc in the presence of K3PO4. The purification involved sequentially Soxhlet extraction, Kauffman column chromatography and train sublimation. We have repeated the process and yields ranged from 27 to 30% of pure, doubly-sublimed µ-oxo-(BsubPc)2. This process also enabled the synthesis of unsymmetric µ-oxo-(BsubPc)2s by reaction of HO-BsubPc with Br-F12BsubPc, Cl-Cl6BsubPc and Cl-Cl12BsubPc. After synthesis the solution-state properties of the unsymmetric µ-oxo-(BsubPc)2s were investigated, and compared to the symmetric µ-oxo-(BsubPc)2 and more broadly to other BsubPcs. The electronic properties of µ-oxo-(BsubPc)2 were found to differ from its unsymmetric counterparts, but were found to be similar to halo-BsubPcs. Furthermore, the photophysical properties of µ-oxo-(BsubPc)2, both symmetric and unsymmetric, differed greatly from all other known BsubPcs.

Bis(tri-n-hexylsilyl oxide) silicon phthalocyanine: a unique additive in ternary bulk heterojunction organic photovoltaic devices.

Previous studies have shown that the use of bis(tri-n-hexylsilyl oxide) silicon phthalocyanine ((3HS)2-SiPc) as an additive in a P3HT:PC61BM cascade ternary bulk heterojunction organic photovoltaic (BHJ OPV) device results in an increase in the short circuit current (J(SC)) and efficiency (η(eff)) of up to 25% and 20%, respectively. The previous studies have attributed the increase in performance to the presence of (3HS)2-SiPc at the BHJ interface. In this study, we explored the molecular characteristics of (3HS)2-SiPc which makes it so effective in increasing the OPV device J(SC) and η(eff. Initially, we synthesized phthalocyanine-based additives using different core elements such as germanium and boron instead of silicon, each having similar frontier orbital energies compared to (3HS)2-SiPc and tested their effect on BHJ OPV device performance. We observed that addition of bis(tri-n-hexylsilyl oxide) germanium phthalocyanine ((3HS)2-GePc) or tri-n-hexylsilyl oxide boron subphthalocyanine (3HS-BsubPc) resulted in a nonstatistically significant increase in JSC and η(eff). Secondly, we kept the silicon phthalocyanine core and substituted the tri-n-hexylsilyl solubilizing groups with pentadecyl phenoxy groups and tested the resulting dye in a BHJ OPV. While an increase in JSC and η(eff) was observed at low (PDP)2-SiPc loadings, the increase was not as significant as (3HS)2-SiPc; therefore, (3HS)2-SiPc is a unique additive. During our study, we observed that (3HS)2-SiPc had an extraordinary tendency to crystallize compared to the other compounds in this study and our general experience. On the basis of this observation, we have offered a hypothesis that when (3HS)2-SiPc migrates to the P3HT:PC61BM interface the reason for its unique performance is not solely due to its frontier orbital energies but also might be due to a high driving force for crystallization.