Electronic properties of small molecule-diketopyrrolopyrrole derivatives and a correlation with the open circuit voltage in organic solar cells

The electronic properties of five diketopyrrolopyrrole (DPP) derivatives as a function of alkyl chains and conjugated frameworks were investigated. The results of ultraviolet photoelectron spectroscopy (UPS) and UV-vis absorption measurements show different ionization potentials (IPs), and optical band gaps. To investigate the relation between the IP and the open circuit voltage (V _OC) of bulk heterojunction (BHJ) solar cells, the V _OC of organic solar cells fabricated with DPP derivatives as the donor and [6,6]-phenyl C ₇₁ butyric acid methyl ester (PC ₇₁BM) as the acceptor were measured. The values between the IP of the DPP derivatives and V _OC in BHJ devices exhibit linear relationship.