Abstract
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 In
2
O
3
and Ga
2
O
3
cathode buffer layers (CBLs). The introduction of In
2
O
3
or Ga
2
O
3
CBLs endows PM6:Y6-based OSCs with outstanding performance and high PCEs of 16.17% and 16.01%, respectively. Comparison studies present that the In
2
O
3
layer possesses a work function (WF) of 4.58 eV, which is more favorable for the formation of ohmic contact compared with the Ga
2
O
3
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 In
2
O
3
and Ga
2
O
3
affect the internal charge transfer and the origin of their performance difference. Although In
2
O
3
possesses lower series resistance loss, Ga
2
O
3
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 In
2
O
3
and Ga
2
O
3
suggests that both are excellent CBLs for highly efficient OSCs.