# Spectral Relationships of ZnPc and CuPc: UV-VIS and Fluorescence Behavior in Liquids and Thin Films

## TL;DR

This study compares two methods for making thin films of ZnPc and CuPc, finding that close space sublimation produces better quality films for optoelectronic uses.

## Contribution

The study introduces CSS as a superior method for fabricating high-quality phthalocyanine thin films with better optical and morphological properties.

## Key findings

- CSS films show high transparency (~90%) and a sharp Q-band around 680 nm.
- CSS films have a fluorescence maximum at ~825 nm with strong emission intensity.
- CSS produces smoother, more uniform films compared to drop casting.

## Abstract

In this study, zinc phthalocyanine (ZnPc) and copper phthalocyanine (CuPc) thin films fabricated by drop casting (DC) and close space sublimation (CSS) have been investigated and compared with ZnPc and CuPc solutions in formic acid (29 µmol/L). The results show that the CSS method produces films with improved molecular ordering, enhanced surface uniformity, superior optical and morphological properties compared to those obtained by drop casting. Moreover, CSS allows a precise and reproducible deposition, resulting in thinner, homogeneous layers with strong substrate adhesion and fewer defects. Optical characterization confirms that CSS films display high transparency (~90%), a sharp Q-band around 680 nm, and a fluorescence maximum at ~825 nm with the strongest emission intensity.In contrast, DC films show lower transparency (<70%), a slightly shifted Q-band (~675 nm), and similar emission around 825 nm. The fluorescence is strongly thickness-dependent: at ~100 nm, the emission band appears at 795 nm, while films thicker than 300 nm exhibit a red-shifted maximum at ~825 nm. AFM analysis further demonstrates the influence of deposition method: CSS yields smoother films with tunable morphology, while DC produces rougher, less controllable surfaces. Overall, CSS is shown to be the more effective approach for fabricating high-quality phthalocyanine films for optoelectronic applications such as photovoltaics and sensors.