Effect of cationic groups in organic sulfide electrolyte on the performance of CdS quantum dot sensitized solar cells

Two organic sulfide redox couples derived from2-mercapto-5-methyl-1,3,4-thiadiazole(McMT):tetrabutylammonium thiolate(McMT-TBA?)/disulfide dimer(BMT)and tetramethylammonium thiolate(McMTTMA?)/BMT were incorporated into quantum dots sensitized solar cells(QDSCs)as alternatives to the inorganic polysulfide electrolyte(Na2S/S).It was found in symmetrical cells test that the interfaces of the organic sulfide electrolytes/platinum counter-electrode have much lower charge transfer resistances as well as higher interface reaction rates compared with that for the inorganic one.Besides,QDSCs based on organic sulfide electrolytes exhibited obviouslyhigher fill factors,open circuit photovoltages,and therefore higher conversion efficiency,thanks to the prohibited recombination and lower redox potential.In addition,by comparing and analyzing the performance of devices based on organic sulfide electrolytes with different cationic groups,it is found that cationic group TMA?with smaller size was favorable for the mass transport in the electrolyte,which explains the better photovoltaic performance of McMT-TMA?/BMT based solar cell than that of McMT-TBA?/BMT based one.Eventually,a power conversion efficiency(PCE)of 0.63%was achieved for QDSCs using McMT-(TMA?)/BMT redox couple as electrolyte,which was till now the highest for CdS QDSC based on organic sulfide electrolyte.