Effect of TADF fluorescent isomers on the solar cell performance and dielectric characteristics of organic Schottky junctions

We have found that some fluorescent small molecules could be used as donor in organic Schottky junctions (OSJs) and achieved good performance. There has been no report on the application of thermally activated delayed fluorescence (TADF) luminescent material on OSJs. In this work, the effect of TADF isomers on the solar cell performance and dielectric characteristics of the OSJs were investigated. All the doped OSJs demonstrate higher Jsc than the neat C 60 OSJ, and 4CzTPN achieves the highest photovoltaic performance. However, the overall efficiency of these OSJs is not so high probably arising from the high photoluminescence quantum yield of these donors. The dielectric characteristics including Z-V, C-V, and Z-f were investigated, and the Z-V characteristic shows a reverse trend with the Jsc. For the C-V characteristics, the first V peak demonstrates a similar trend with the open circuit voltage and the built-in potential. The 4CzPN OSJ depicts much higher capacitance for the second peak than the 4CzIPN and 4CzTPN based OSJs, indicating the existence of more traps, resulting in a relatively low Jsc. For Z-f characteristics, the impedance of the doped OSJs is slightly lower from 20 Hz to 107 Hz than the neat C 60 OSJ.