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.