Photoconductivity of a Low‐Bandgap Conjugated Polymer

Abstract

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.

Double acceptor donor–acceptor alternating conjugated polymers containing cyclopentadithiophene, benzothiadiazole and thienopyrroledione: toward subtractive color organic photovoltaics

“…5,[30][31][32][33][34][35][40][41][42][43] On this basis, when BT and TPD are assembled together in a repeating polymer unit, we expect that the energy levels of the polymer could be tailored to give a wide photo absorption range with alterations to the TPD moiety, resulting in changes to the HOMO energy level and changes in the BT unit, resulting in the alteration of the absorption at higher wavelengths. While new D-A units and their combinations have been investigated, improved molecular designs incorporating further combinations of D-A units are possible but have so far not been well-reported.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Benzothiadiazole (BT) and its analogs have been used as electron acceptor groups in conjunction with various donor units such as cyclopentadithiophene (CPDT); compounds containing these acceptor groups exhibit lower-energy levels and a reduction in the band gap compared with other D-A alternating copolymers. [23][24][25][26][27][28][29] Since the development of poly [4,4- Figure 1), one of the first efficient third-generation donor-type conjugated polymers, [30][31][32][33][34][35] various new conjugated polymers applying D-A structures have been synthesized. These feature a lower-energy band gap to capture a wider range of the solar spectrum.…”

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

“…NIR photodetectors are important in medical, industrial, communication, scientific and military applications as well as for night-vision imaging and security [14][15][16] . NIR-sensitive photodectectors have previously been demonstrated using inorganic quantum dot sensitization 17,18 , narrow optical-gap donor organic semiconductors within a conventional thin heterojunction structure 14,19,20 , and more recently by harvesting sub-gap charge transfer states (CT) 15,21,22 . Yang et al have reported on the use of CT state absorption to extend the spectral response of an OPD based on a P3HT:PC60BM blend to the NIR 22 .…”

A Polymer with a Benzo[2,1‐b;3,4‐b′]dithiophene Moiety for Photovoltaic Applications

“…For an efficient solar cell, the HOMO and the LUMO energies of donors should be more positive than those of acceptors in order to guarantee a ready charge transfer in the device. [12] Therefore, [70]PCBM, with an experimentally determined LUMO level of À4.3 eV and a HOMO level of À6.1 eV, was chosen as acceptor. In the pair, a 0.9 eV offset of HOMO levels and a 1. annealing, the PBTT-based bulk-heterojunction solar cells show an overall conversion efficiency of 2.7 % under 1 sun light illumination.…”