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 (VOC) device and provides another method to realize high‐power conversion efficiency in organic solar cells. However, the VOC 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 VOC 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 VOC devices, and also provides a reference for other semiconductor optoelectronic devices. [ABSTRACT FROM AUTHOR]