Cellulose Nanocrystals-Tin-Oxide Hybrid Electron Transport Layers for Solar Energy Conversion

Petro-derived organic cathode interlayers (CILs) can modify the tin-oxide (SnO2) electron transport layer (ETL) in organic photovoltaics (OPVs) to address the energy-level alignment, charge extraction, and device shelf-life instability challenges. However, the potential eco-hazardousness of petro sources used to synthesize such CILs and the toxicity of processing solvents warrant the discovery of sustainable and commercially viable substitutes. Herein, a low-cost, biocompatible, and water-processable CIL based on amine-functionalized cellulose nanocrystals (CNC-a) is introduced to enhance the performance of OPVs by mitigating surface defects of the SnO2 ETL. X-ray photoelectron spectroscopy (XPS) reveals a reduction in water traps after SnO2 modification with CNC-a. The electrical characterization shows that CNC-a modification improves the conductivity of the SnO2. CNC-a inhibits charge recombination and improves the charge collection ability leading to power conversion efficiencies (PCEs) of >13% in halogen-free solvent and air-processed PBDB-T-SF (PM6):BTP-4F-12 (Y6-C12)-based OPVs. The SnO2/CNC-a bilayer ETL-based devices exhibit relatively high shelf-life device stability. Fully slot-die-coated (where SnO2, CNC-a, and bulk heterojunction [PM6:Y6-C12] are coated) large area bottom cathode cells (PCE > 10%) are demonstrated, showcasing the utility for scale-up. This work opens a viable and sustainable pathway to develop bio-derived materials for scalable OPVs.

Automated summary

This study introduces a low-cost, biocompatible, and water-processable organic photovoltaic (OPV) modification material based on amine-functionalized cellulose nanocrystals, which can improve the performance and shelf-life stability of the SnO2 electron transport layer in OPVs.