Improving Polymer/Nanocrystal Hybrid Solar Cell Performance via Tuning Ligand Orientation at CdSe Quantum Dot Surface

Abstract

Achieving superior solar cell performance based on the colloidal nanocrystals remains challenging due to their complex surface composition. Much attention has been devoted to the development of effective surface modification strategies to enhance electronic coupling between the nanocrystals to promote charge carrier transport. Herein, we aim to attach benzenedithiol ligands onto the surface of CdSe nanocrystals in the "face-on" geometry to minimize the nanocrystal-nanocrystal or polymer-nanocrystal distance. Furthermore, the "electroactive" π-orbitals of the benzenedithiol are expected to further enhance the electronic coupling, which facilitates charge carrier dissociation and transport. The electron mobility of CdSe QD films was improved 20 times by tuning the ligand orientation, and high performance 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):CdSe nanocrystal hybrid solar cells were also achieved, showing a highest power conversion efficiency of 4.18%. This research could open up a new pathway to improve further the performance of colloidal nanocrystal based solar cells.

Phosphate ester side‐chain‐modified conjugated polymer for hybrid solar cells

“…2,6‐Dibromo‐ 4,4‐ bis (6‐bromohexyl)−4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene was synthesized according to the reported procedures . CdSe QDs was prepared to the literature …”

“…But they are detrimental to charge transfer and transport. Thus ligand engineering has been developed to solve this problem, including colloidal ligand exchange and postdeposition ligand exchange . Both methods intend to replace the long chain ligands with shorter ones and reduce the distance between polymers and QDs to improve the charge transfer.…”

Bulk Heterojunction Solar Cells Based on Blends of Conjugated Polymers with II–VI and IV–VI Inorganic Semiconductor Quantum Dots

“…Stabilizing ligands with long alkyl chains such as oleic acid and oleylamine are used in colloidal QD synthesis to solubilize the nanocrystals, control their size and protect them from undesirable chemical reactions. However when QD films are cast along with conjugated polymers to form a photovoltaic device, the stabilizing ligands—which are insulating—inhibit exciton dissociation and charge transport [85]. There has been a concerted move in the hybrid solar cell field to move to replace long chain ligands stabilizing CQDs by shorter chain and aryl-type ligands capable of effective π-overlap.…”

Aqueous‐Processed Polymer/Nanocrystals Hybrid Solar Cells: The Effects of Chlorine on the Synthesis of CdTe Nanocrystals, Crystal Growth, Defect Passivation, Photocarrier Dynamics, and Device Performance

“…Nanoscale morphology control of polymer/NCs hybrid films is difficult due to the inferior miscibility of polymer and NCs. Some methods are developed to solve this problem to some degree, such as ligand exchange, mixed solvent, and precursor motheds .…”