Controlled Fabrication of PbS Quantum‐Dot/Carbon‐Nanotube Nanoarchitecture and its Significant Contribution to Near‐Infrared Photon‐to‐Current Conversion

Abstract

A solution‐processed nanoarchitecture based on PbS quantum dots (QDs) and multi‐walled carbon nanotubes (MWCNTs) is synthesized by simply mixing the pre‐synthesized high‐quality PbS QDs and oleylamine (OLA) pre‐functionalized MWCNTs. Pre‐functionalization of MWCNTs with OLA is crucial for the attachment of PbS QDs and the coverage of QDs on the surface of MWCNTs can be tuned by varying the ratio of PbS QDs to MWCNTs. The apparent photoluminescence (steady‐state emission and fluorescence lifetime) “quenching” effect indicates efficient charge transfer from photo‐excited PbS QDs to MWCNTs. The as‐synthesized PbS‐QD/MWCNT nanoarchitecture is further incorporated into a hole‐conducting polymer poly(3‐hexylthiophene)‐(P3HT), forming the P3HT:PbS‐QD/MWCNT nanohybrid, in which the PbS QDs act as a light harvester for absorbing irradiation over a wide wavelength range of the solar spectrum up to near infrared (NIR, ≈1430 nm) range; whereas, the one‐dimensional MWCNTs and P3HT are used to collect and transport photoexcited electrons and holes to the cathode and anode, respectively. Even without performing the often required “ligand exchange” to remove the long‐chained OLA ligands, the built nanohybrid photovoltaic (PV) device exhibits a largely enhanced power conversion efficiency (PCE) of 3.03% as compared to 2.57% for the standard bulk hetero‐junction PV cell made with P3HT and [6,6]‐Phenyl‐C61‐Butyric Acid Methyl Ester (PCBM) mixtures. The improved performance of P3HT:PbS‐QD/MWCNT nanohybrid PV device is attributed to the significantly extended absorption up to NIR by PbS QDs as well as the effectively enhanced charge separation and transportation due to the integrated MWCNTs and P3HT. Our research results suggest that properly integrating QDs, MWCNTs, and polymers into nanohybrid structures is a promising approach for the development of highly efficient PV devices.

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

“…The short-circuit current density (J sc ), opencircuit voltage (V oc ) and fill factor (FF) of this control device were measured to be 8.82 mA/cm 2 , 0.54 V and 54%, respectively, as enlisted in Table 1. Power conversion efficiency (PCE) of 2.57% was evaluated from these measurements which is an appropriate value for PV cells fabricated and characterized upon air exposure and also comparable with our previously reported results [31,33]. Next, we fabricate the hybrid device -I upon merely adding hybridized PbS-QD/MWCNTs into the standard polymer/fullerene (P3HT:PCBM) blend.…”

“…[31][32][33]. The measured photocurrent density (J) as a function of applied voltage (V) of the standard PV cell, illuminated under AM1.5G solar spectrum at intensity of 100 mW cm −2 , is shown in Figure 1.…”

“…However, beyond 1450 nm, J sc value drastically decreases and is nil beyond 1700 nm. It is then clearly seen from the Figure 2a that the J sc values measured for wavelength between 650 nm to 1450 nm in hybrid device -I should be due to charges generated in the presence of quantum-dot-sensitized PbS [31]. In Figure 2b, the wavelength resolved open circuit voltage (V oc ) measurements were carried out on those same standard and hybrid devices at different wavelengths, similar effect for V oc was observed as it was observed for J sc in Figure 2a.…”

“…In one of our previous communication [31], where we have reported a hybrid photoactive layer prepared from a modified blend of P3HT (without PCBM) and nanohybridized PbS/MWCNT, in place of standard P3HT: PCBM. The P3HT:PbS/MWCNT solar cell shown an improved PCE enhancement while PCBM was replaced by nanohybridized PbS/MWCNT.…”

“…2 Experimental details and device fabrication 2.1 Chemical synthesis of PbS-QDs by using OLA as ligands PbS QDs were synthesized by an organometallic chemistry method using OLA as ligands [31,32]. Typically, PbCl 2 (278 mg, 1 mMol, Sigma-Aldrich) and OLA (5 mL, SigmaAldrich, technical grade, 70%) were loaded into a 50 mL three-neck flask at room temperature.…”