Photoconductivity of a Low-Bandgap Conjugated Polymer


  • Research at UCSB was supported by a grant from Konarka Technologies, Inc., and by the AirForce Office of Scientific Research (Charles Lee, Program Officer). The assistance of Dr. Alexander Mikhailovsky in photoluminescence measurements is gratefully acknowledged. We also thank Wanli Ma, Dr. Jin Young Kim and Dr. Cuiying Yang for the useful discussions.


The photoconductive properties of a novel low-bandgap conjugated polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT, with an optical energy gap of Eg ∼ 1.5 eV, have been studied. The results of photoluminescence and photoconductivity measurements indicate efficient electron transfer from PCPDTBT to PCBM ([6,6]-phenyl-C61 butyric acid methyl ester, a fullerene derivative), where PCPDTBT acts as the electron donor and PCBM as the electron acceptor. Electron-transfer facilitates charge separation and results in prolonged carrier lifetime, as observed by fast (t > 100 ps) transient photoconductivity measurements. The photoresponsivities of PCPDTBT and PCPDTBT:PCBM are comparable to those of poly(3-hexylthiophene), P3HT, and P3HT:PCBM, respectively. Moreover, the spectral sensitivity of PCPDTBT:PCBM extends significantly deeper into the infrared, to 900 nm, than that of P3HT. The potential of PCPDTBT as a material for high-efficiency polymer solar cells is discussed.