Broadband Absorbing Bulk Heterojunction Photovoltaics Using Low-Bandgap Solution-Processed Quantum Dots

Abstract

We describe bulk heterojunction (BHJ) solar cells containing blends of colloidal PbS nanocrystal quantum dots with several new donor-acceptor conjugated polymers. Using photoinduced absorption spectroscopy we found that blends of PbS quantum dots with one polymer, poly(2,3-didecyl-quinoxaline-5,8-diyl-alt-N-octyldithieno[3,2-b:2',3'-d]pyrrole) (PDTPQx), produce significantly more photoinduced charge than blends of PbS with the other donor-acceptor polymers or with traditionally studied polymers like [2-methoxy-5-(3',7'-dimethyloctyloxy)-para-phenylene vinylene] (MDMO-PPV) and poly(3-hexylthiophene) (P3HT). Photovoltaic devices made with PDTPQx/PbS blends exhibit power conversion efficiencies 10-100 times larger than previously reported BHJ blends made with IR-absorbing quantum dots.

Enhanced photovoltaic conversion efficiency in bulk heterojunction solar cells upon incorporating nanohybridized PbS quantum dots/multiwall carbon nanotubes

“…We presume that the V oc can be attributed to the energy difference between the HOMO of P3HT and LUMO of PCBM in our standard cell as it has been reported by other research groups [42][43][44][45][46][47]. Since the value of conduction band of PbS-QDs is consistently aligned with the LUMO value of PCBM [1,14,28] as shown in Figure 7, therefore it is obvious that the V oc of hybrid device -I is consistent with the standard P3HT:PCBM devices. This explains the charge transfer takes place at P3HT/PCBM interface in the case of standard devices, whereas the same phenomenon of charge transfer occurs at the interface(s) of P3HT/PbS and/or P3HT/(PCBM/PbS) in case of the hybrid devices.…”

“…A schematic illustration is depicted in Figure 7, with all the photoactive materials used in this experiment along with their respective energy levels [1,14,28,31,33,37,38], in order to explain the working mechanism(s). In a ternary nanoblend of (P3HT:PCBM):PbS/MWCNT, it has been reported that there is almost a flat band condition between the LUMO of PCBM and the conduction band of PbS-QDs [14,39] as shown in Figure 7.…”

“…Energy band diagram displaying HOMO and LUMO of polymer donor-acceptor materials, as well as the valence and conduction band edge of inorganic PbS-QD acceptor. Values were taken from the references [1,14,28,31,33,37,38].…”

“…We explain the charge transport mechanism(s) behind the consistently observed V oc in all our devices with the aid of energy band diagram shown in Figure 7. The energy level values were taken from the references elsewhere [1,14,28,31,33,37,38]. In all our devices, the P3HT was used as donor with respect to the PCBM and/or nanohybrid of QD/CNT as the acceptor(s).…”

“…Polymer solar cells are emerging as the alternative inexpensive renewable source of green energy due to their interesting properties, such as, low-temperature based manufacturing, mechanical flexibility and solution processability [1][2][3][4][5][6][7][8][9][10][11][12]. Recently, the power conversion efficiency (PCE) of OPV devices has exceeded the 10% milestone [11,12].…”