Direct Z-Characteristic Observation and Efficiency Improvement in Organic Solar Cells with Ethylenediamine Regulating the Unconventional Energy-Level Alignment

According to the previous study, a bilayer organic photovoltaic with unconventional energy-level alignment has been studied. Unlike the donor-acceptor system, this kind of structure has the potential to produce a high open-circuit voltage (V-OC) device and provides another method to realize high-power conversion efficiency in organic solar cells. However, the V-OC of the device is not high enough, and there is no direct observation of the Z-characteristic. Herein, the device performance is improved according to the strategy provided in the latest report. With ethylenediamine regulating the interface, the V-OC and short-circuit current are improved from 0.59 to 0.77 V and 0.9 to 1.9 mA cm(-2), respectively. The overall efficiency increases by 280%. The enhancement and direct observation of Z-characteristics are observed. Considering the efficiency improvement brought by Z-characteristic enhancement in this work, combined with the previous work, the theoretical efficiency limitation is 22.5% under a low light intensity and 30% under a high light intensity. This article supports the previous work, shows that the Z-characteristic device has very broad optimization potential, provides a method for the fabrication of high efficiency and high V-OC devices, and also provides a reference for other semiconductor optoelectronic devices.