3.?Results and DiscussionsThe narrow-band gap semiconducting polymer, PCPDTBT (Scheme 1a), has broad band absorption at the wavelengths �� = 300�C950 nm, with a cutoff at �� �� 1,000 nm (Figure 1), high photoconductivity. quality control Good solar cell performance is obtained by blending it with PC70BM [12].Figure 1.Absorption spectra (left) of pristine PCPDTBT and PCPDTBT:PC70BM thin films, and EQE (right) from the device with the following structure: ITO/PEDOT:PSS/PCPDTBT:PC70BM/Al. The EQE was measured at zero bias.The photo-active layer in our PPDs comprises a phase separated blend of PCPDTBT and PC70BM. The two components form interpenetrating Inhibitors,Modulators,Libraries donor/acceptor networks in the bulk heretojunction (BHJ) structure.

Three different PPD architectures were investigated:PPD A: ITO/PEDOT:PSS/PCPDTBT: PC70BM/Al;PPD B: ITO/PEDOT:PSS/PCPDTBT: PC70BM/C60/Al Inhibitors,Modulators,Libraries andPPD C: ITO/PEDOT:PSS/PS-TPD-PFCB/PCPDTBT: PC70BM/C60/Al.These three device architectures are shown in Scheme 1b (the thickness of each layer is indicated). The energy level diagram in Scheme 1c shows the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of PCPDTBT, PC70BM, C60 and PS-TPD-PFCB. The workfunctions of PEDOT:PSS and Al are also shown in Scheme 1c. The difference between the LUMOs of PCPDTBT and PC70BM is ~0.8 eV, which ensures photoinduced charge transfer and charge separation in the PCPDTBT:PC70BM BHJ structure [14].The current-density voltage (J�CV) characteristics measured in the dark and under illumination (�� = 800 nm) with light intensity of 0.22 mW/cm2 are shown in Figure 2.

All PPDs (A, B and C) Inhibitors,Modulators,Libraries show good rectification ratios in the dark, 104 at ��1 V, indicating the formation of good diodes. The dark currents observed from PPD B are more than 2 orders of magnitude smaller than that from PPD A; the dark currents observed from PPD C are more than 10 times smaller than that from PPD B. These results indicate that the thin C60 and PS-TPD-PFCB buffer layers are important for minimizing the dark currents generated withinfrom the PCPDTBT:PCBM PC70BM BHJ structure.Figure 2.Current-density-voltage characteristics of polymer photodetectors measured in the dark (Jd) Inhibitors,Modulators,Libraries and under light (Jph); �� = 800nm with intensity of 0.

22 mW/cm2For PPDs A, B and C, the current density (J)�Cvoltage (V) relationship can AV-951 be described by the standard diode equation [15]:J=?J0exp[q(V+JRS)nKBT]?1?V+JRSRSE(1)whereJ0=A*T2exp(?EPFKBT)(2)and A* = 4��qm*KB2/h3, J0 is the saturation current density, q is the electron charge V is the voltage, selleck compound n is the ideality factor, KB is the Boltzman constant, T is the absolute temperature RS is the series resistance, RSH is the shunt resistance, m* is the effective electron mass, h is Planck��s constant, A* is Richardson��s constant and EPF is the energy difference between the HOMO of PCPDTBT and the LUMO of PC70BM (~0.6 eV).As described above, a high dark current is expected from PPD A because EPF (~0.6 eV) is relatively small.