Early-stage analysis of PET – fullerene derivatives for electron transport in photovoltaics

Abstract

In the pursuit of sustainable materials for solar cell technologies, this work presents a new class of electron transport layers (ETLs) based on PET-derived monomers and dimers hybridized with fullerene C₆₀. These hybrids were synthesized via selective cyclopropane and furan functionalization and thoroughly characterized using electrochemical, optical, and morphological methods. Compared to the benchmark material PCBM, several PET–fullerene derivatives exhibited improved properties, including enhanced substrate coverage, stronger electron-blocking behaviour, and favourable energy level alignment. Compound 5 emerged as the most promising ETL candidate, demonstrating a smooth, pinhole-free morphology (RMS = 1.15 nm), high charge transfer resistance (R_ct = 8.63 × 10⁴ Ω), and a relatively high apparent donor density (N_d = 2.21 × 10²¹ cm⁻³). While the absolute N_D values may be influenced by film morphology, the comparative analysis confirms superior performance of compound 5. These results indicate that PET–fullerene hybrids, especially compound 5, offer both environmental and functional advantages as next-generation ETL materials.