Solution-processed small-molecule organic solar cells based on non-aggregated zinc phthalocyanine derivatives: A comparative experimental and theoretical study

Abstract

A series of non-aggregated zinc phthalocyanine derivatives containing either bulky thiophenol or phenol substituents were synthesized as a novel donor component for bulk heterojunction (BHJ) solar cell applications. The molecular structure and photophysical properties of ZnPc derivatives were investigated by combined experimental and theoretical studies using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. In order to evaluate the physical properties of ZnPcs in the solvent environment, we applied the conductor-like polarizable continuum model (CPCM). Within this scope, light-harvesting efficiency (LHE), excited-state lifetime (τ), maximum absorption wavelengths (λmax), oscillator strength (f) and hyperpolarizability (β tensors) were calculated both in vacuum and chloroform (ε = 4.9) medium. Furthermore, divergent types of global descriptors such as EHOMO, ELUMO, and bandgap (Egap) energies, ionization potential (I), electron affinity (A), hardness (η), and electrophilicity index (ω) were also calculated. Our computational findings revealed that the linker heteroatoms [sulfur for the ZnPc (1–2); oxygen for the ZnPc (3–4) including the substituent type (isopropyl for the ZnPc (2–4), and phenyl for the ZnPc (1–3] severely affected the photophysical properties of the dyes. In relation, theoretical results are in good accordance with our experimental observations. Finally, ZnPc derivatives were used as a donor component and PC61BM as an acceptor material in BHJ solar cells, displaying a maximum power conversion efficiency of 0.8%. Compared with ZnPcs 1–2, ZnPc 3–4 based cells showed an inferior photovoltaic performance. These results are promising and should encourage further studies on BHJ solar cells using near-infrared absorbing and non-aggregated ZnPcs.