Thermodynamic Property–Performance Relationships in Silicon Phthalocyanine-Based Organic Photovoltaics

Abstract

Axially substituted silicon phthalocyanines [(R3SiO)2-SiPc] have recently emerged as promising alternatives to fullerenes in organic photovoltaics (OPVs), with advances in both molecular design and device fabrication resulting in a fourfold improvement in efficiency, bringing these materials closer to commercial viability. Further refinements in SiPc-based OPVs can only be achieved through exploration of their physical properties and correlation with performance metrics. In this work, we have synthesized seven (R3SiO)2-SiPc derivatives and paired them with P3HT in OPV devices to explore how both the fundamental thermodynamic properties of the SiPcs and the blend morphology affect device performance. From these studies, (R3SiO)2-SiPc derivatives with smaller critical radius (r c) values correlated to higher power conversion efficiencies (PCEs) in devices due to their tendency to form smaller domains in the active layer. Higher values for the Flory–Huggins miscibility parameter also correlated to higher PCEs due to the formation of unadulterated, sharper domains. Both properties are dependent upon axial substituent size, with values minimized by smaller axial substituents, serving as a guideline for the molecular design of SiPc-based non-fullerene acceptors (NFAs). Moreover, the majority of the (R3SiO)2-SiPc materials reported herein outperformed the fullerene-based reference device, with one derivative resulting in a device with a PCE greater than 4%.

From P‐type to N‐type: Peripheral fluorination of axially substituted silicon phthalocyanines enables fine tuning of charge transport

“…The champion devices achieved a power conversion efficiency (PCE) of 3.3%, which is comparable to other R 2 ‐SiPc‐based devices. [ 25 ] These results demonstrate that peripheral fluorination of R 2 ‐F x SiPc enables the pairing with PTQ10, by deepening their HOMO/LUMO levels. That is further evidenced by the results obtained from the incorporation of (tb‐Ph) 2 ‐F 4 SiPc in OPDs, also paired with PTQ10 (Figure 4D and Table 3).…”

“…The OPV preparation procedure has been adapted from Vebber et al [ 25 ] Substrate, transport layers, and electrode deposition have not been altered, with overall device structure ITO/ZnO/PTQ10:(tb‐Ph) 2 ‐F x SiPc/MoO X /Ag. Active layers were spin coated at 1250 RPM, for 60 s, from PTQ10:(tb‐Ph) 2 ‐F x SiPc solutions at 8 mg mL −1 and 1:1 ratio.…”

High Performance Solution Processed n‐Type OTFTs through Surface Engineered F–F Interactions Using Asymmetric Silicon Phthalocyanines

“…In particular, axially substituted silicon phthalocyanines (SiPcs) employing flexible nonconjugated alkyl chains as solubilizing groups have demonstrated promising results in n-type OTFTs [27,28] and as acceptors in organic photovoltaic devices (OPV). [29][30][31][32] Substituted alkyl chains contribute to the dissolution of small molecules in solution through increased van der Waals interactions, hindering interactions between the π-conjugated systems of the semiconductor, and thus enabling increased solubility and solution processability. [33] Additionally, SiPcs offer two chemical handles in the axial position enabling the potential for asymmetric substitutions and the incorporation of fluorine atoms for selfpatterning potential and as electron withdrawing groups for enhanced stability.…”

Low-Cost Silicon Phthalocyanine as a Non-Fullerene Acceptor for Flexible Large Area Organic Photovoltaics

“…Phthalocyanines are common dye molecules which have been utilized as a semiconducting material in organic light emitting diodes, , organic thin film transistors − and organic photovoltaics. − Phthalocyanines (Pcs) are already synthesized on the ton scale annually and found in everyday textiles, paints, colorants, and inks . Silicon phthalocyanine ((R) 2 -SiPc) are emerging as an exciting class of phthalocyanines due to their ability to enable n-type operation in electronics and their axial groups provide a handle to tune the physical and thermodynamic properties such as miscibility, solubility, nucleation, and solid-state arrangement. − In terms of synthetic complexity (SC), SiPcs have been reported with an SC index of 12, almost five times lower than those of high-performing NFAs such as Y6 (SC of 59) and ITIC (SC of 67) . Traditionally, (R) 2 -SiPcs have been utilized as ternary additives in donor–acceptor OPVs, providing more than 20% increase in photocurrent due to the extended solar absorption ,− Recently, (R) 2 -SiPc derivatives have also been used as NFAs with different donor polymers P3HT, PTB7, and PBDB-T and achieved high power conversion efficiencies (>4%). , These promising results demonstrate a great potential for low cost OPVs through the use of materials that have low synthetic complexity.…”

“… 28 Silicon phthalocyanine ((R) 2 -SiPc) are emerging as an exciting class of phthalocyanines due to their ability to enable n-type operation in electronics and their axial groups provide a handle to tune the physical and thermodynamic properties such as miscibility, solubility, nucleation, and solid-state arrangement. 29 − 33 In terms of synthetic complexity (SC), SiPcs have been reported with an SC index of 12, almost five times lower than those of high-performing NFAs such as Y6 (SC of 59) and ITIC (SC of 67). 34 Traditionally, (R) 2 -SiPcs have been utilized as ternary additives in donor–acceptor OPVs, providing more than 20% increase in photocurrent due to the extended solar absorption 25 , 35 − 38 Recently, (R) 2 -SiPc derivatives have also been used as NFAs with different donor polymers P3HT, PTB7, and PBDB-T and achieved high power conversion efficiencies (>4%).…”