Capacitance Spectroscopy for Quantifying Recombination Losses in Nonfullerene Small-Molecule Bulk Heterojunction Solar Cells

The light intensity dependence of the main photoelectrical parameters of the nonfullerene small‐molecule bulk heterojunction (BHJ) solar cells p‐DTS(FBTTh2)2:perylene diimide (T1:PDI) shows that the nongeminate recombination losses play an important role in this system. A simple approach for the quantitative analysis of capacitance spectroscopy data of the organic BHJ solar cells, which allows to determine the density of free charge carriers as a function of applied bias under standard working conditions, is demonstrated. Using the proposed capacitance spectroscopic technique, the nongeminate recombination losses in the T1:PDI solar cells are quantitatively characterized in the scope of the bimolecular‐ and trap‐assisted recombination mechanisms. Their contributions are separately analyzed within a wide range of the applied bias. A simple method for the determination of the density of free charge carriers and quantification of nongeminate recombination losses in organic‐bulk heterojunction solar cells, based on the analysis of capacitance spectroscopy data, is presented. The proposed method is applied to the analysis of nongeminate recombination losses in nonfullerene T1: perylene diimide small‐molecule solar cells in the scope of bimolecular‐ and trap‐assisted recombination mechanisms under 1 sun illumination.