γ‐Ray Irradiation Enables Annealing‐ and Light‐Soaking‐Free Solution Processable SnO2 Electron Transport Layer for Inverted Organic Solar Cells

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2024-05, Vol.20 (18), p.e2307441-n/a
• Main Authors: Tran, Hong Nhan, Park, Chan Beom, Lee, Jin Hee, Seo, Jung Hwa, Kim, Jin Young, Oh, Seung‐Hwan, Cho, Shinuk
• Format: Article
• Language: English
• Subjects: Annealing; Buffer layers; Charge transport; Electrodes; Electron mobility; Electron transport; Energy levels; Flexible components; High temperature; Irradiation; Ligands; Nanoparticles; organic solar cell; Photovoltaic cells; room temperature; Soaking; Solar cells; Substrates; Surfactants; Temperature; Thin films; Tin dioxide; tin oxide; γ‐ray radiation
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202307441

The electrode buffer layer is crucial for high‐performance and stable OSCs, optimizing charge transport and energy level alignment at the interface between the polymer active layer and electrode. Recently, SnO2 has emerged as a promising material for the cathode buffer layer due to its desirable properties, such as high electron mobility, transparency, and stability. Typically, SnO2 nanoparticle layers require a postannealing treatment above 150°C in an air environment to remove the surfactant ligands and obtain high‐quality thin films. However, this poses challenges for flexible electronics as flexible substrates can't tolerate temperatures exceeding 100°C. This study presents solution‐processable and annealing‐free SnO2 nanoparticles by employing y‐ray irradiation to disrupt the bonding between surfactant ligands and SnO2 nanoparticles. The SnO2 layer treated with y‐ray irradiation is used as an electron transport layer in OSCs based on PTB7‐Th:IEICO‐4F. Compared to the conventional SnO2 nanoparticles that required high‐temperature annealing, the y‐SnO2 nanoparticle‐based devices exhibit an 11% comparable efficiency without postannealing at a high temperature. Additionally, y‐ray treatment has been observed to eliminate the light‐soaking effect of SnO2. By eliminating the high‐temperature postannealing and light‐soaking effect, y‐SnO2 nanoparticles offer a promising, cost‐effective solution for future flexible solar cells fabricated using roll‐to‐roll mass processing. Annealing‐free and light‐soaking‐free tin dioxide (SnO2) electron transport layers are developed and applied to non‐fullerene organic solar cells (OSCs) based on PTB7‐Th:IEICO‐4F. The OSCs fabricated with pristine SnO2 exhibited 8.34% low efficiency without annealing. However, upon annealing the pristine SnO2 at 150 °C, the efficiency recovered to the normal value of 11.21%. The solar cell using γ‐ray treated SnO2 demonstrated a comparable efficiency of 11.18% without any annealing process. Furthermore, the light‐soaking effect disappeared in the γ‐ray‐treated SnO2.