Efficient organic solar cells with low-temperature in situ prepared Ga₂O₃ or In₂O₃ electron collection layers

Facile synthesis of an interfacial layer in organic solar cells (OSCs) is important for broadening material designs and upscaling photovoltaic conversion efficiency (PCE). Herein, a mild solution process of spin-coating In(acac)₃ and Ga(acac)₃ isopropanol precursors followed by low-temperature thermal treatment was developed to fabricate In₂O₃ and Ga₂O₃ cathode buffer layers (CBLs). The introduction of In₂O₃ or Ga₂O₃ CBLs endows PM6:Y6-based OSCs with outstanding performance and high PCEs of 16.17% and 16.01%, respectively. Comparison studies present that the In₂O₃ layer possesses a work function (WF) of 4.58 eV, which is more favorable for the formation of ohmic contact compared with the Ga₂O₃ layer with a WF of 5.06 eV and leads to a higher open circuit voltage for the former devices. Electrochemical impedance spectroscopy was performed to reveal how In₂O₃ and Ga₂O₃ affect the internal charge transfer and the origin of their performance difference. Although In₂O₃ possesses lower series resistance loss, Ga₂O₃ has a higher recombination resistance, which enhances the device fill factor and compensates for its series resistance loss to some extent. Comparative analysis of the photo-physics of In₂O₃ and Ga₂O₃ suggests that both are excellent CBLs for highly efficient OSCs.