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

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.