An inorganic molecule-induced electron transfer complex for highly efficient organic solar cells†
Interfacial engineering of electrode modification has proved to be an effective approach for improving the power conversion efficiency (PCE) of organic solar cells (OSCs). However, compared to the advances in active layers, the study of interfacial modification is seriously lagging and the contribution of electrode modification to PCE enhancement is marginalized. Herein, we synthesized a series of polynuclear metal-oxo clusters (PMCs) with gradually varied chemical compositions and photoelectronic properties, by which an efficient and stable hole extraction layer was developed to enhance OSC efficiency. The PCE of the OSC modified by PMC-4 was improved from 15.7% to 16.3% as compared to the PEDOT:PSS device. Moreover, PMC-4 can be fabricated through solution processing without any post-treatment and the corresponding device shows improved long-term stability. As revealed for the first time, the strong oxidizing property of PMC can induce formation of an inorganic–organic electron transfer complex with a barrier-free interface for efficient hole extraction. Furthermore, experimental data and theoretical calculation results reveal that the molecular polarization of mixed-addenda PMCs can enhance the capacitance at the AIL/active layer interfaces. As a result, the mixed-addenda PMCs can be processed via blade-coating to make a large-area OSC of 1 cm2 and a certified PCE of 14.3% was achieved.