Auxiliary donors for phenothiazine sensitizers for dye-sensitized solar cells – how important are they really?†
Auxiliary donors are common design motifs for phenothiazine sensitizers for dye-sensitized solar cells. Despite this, there are only a few reports on their overall contribution to the photon-to-electron conversion efficiency. Twelve sensitizers have been prepared and investigated, including ten different auxiliary donors in addition to a control with no auxiliary donor. The various auxiliary donors improved the PCE by a modest 4–11%, and pyrene (AFB-19) was determined to be the most efficient auxiliary donor, with the best cell delivering a PCE of 5.36%. Included in the dye series was also the champion dye within the phenothiazine class. With a reported PCE of 12.1%, it would be an excellent phenothiazine reference dye. The high VOC of 0.83 V of this dye is worth further investigation, but the absorption and photovoltaic performance in this work does not correlate with the previously reported PCE of 12.1%.