Novel Hybrid Ligands for Passivating PbS Colloidal Quantum Dots to Enhance the Performance of Solar Cells.

Yuehua Yang,Hongbin Wu,Yuping Gao,Donghuan Qin,Lintao Hou,Yiyao Tian,Wenbo Huang,Baofeng Zhao,Han Liu

doi:10.1007/s40820-015-0046-4

Yuehua Yang, Hongbin Wu + Show 7 more

Open Access

https://doi.org/10.1007/s40820-015-0046-4

Copy DOI

Abstract

We developed novel hybrid ligands to passivate PbS colloidal quantum dots (CQDs), and two kinds of solar cells based on as-synthesized CQDs were fabricated to verify the passivation effects of the ligands. It was found that the ligands strongly affected the optical and electrical properties of CQDs, and the performances of solar cells were enhanced strongly. The optimized hybrid ligands, oleic amine/octyl-phosphine acid/CdCl2 improved power conversion efficiency (PCE) to much higher of 3.72 % for Schottky diode cell and 5.04 % for p–n junction cell. These results may be beneficial to design passivation strategy for low-cost and high-performance CQDs solar cells.

Highlights

Colloidal quantum dots (CQDs) solar cells as potential next-generation solar energy-harvesting devices have received considerable attention in the past several years [1,2,3,4] owing to their low manufacturing cost
PbS CQDs solar cells can be prepared in ambient condition under low temperatures below 200 °C, and the electronic bandgap of PbS CQDs can be tuned by changing size due to its large exciton Bohr radius (*18 nm for PbS [19]), which enables the fabrication of multi-junction solar cells from single material
The peaks blue shifted for those with hybrid ligands and the blue-shift amplitudes increase with increasing carboxyl chain of passivating ligands (998 nm for ligand B, 1040 nm for ligand C, and 1060 nm for ligand D). This may be due to the stronger absorption ability of the alkyl phosphate acid ligands with shorter carboxyl chains which could slow down the growth rate of PbS CQDs

Summary

Introduction

Colloidal quantum dots (CQDs) solar cells as potential next-generation solar energy-harvesting devices have received considerable attention in the past several years [1,2,3,4] owing to their low manufacturing cost (coated on substrates using drop-casting, spin-coating or ink-jet printing). Since the long-chain carboxyl acid is usually attached to the surface of PbS, it is difficult to gain satisfactory device performance unless the carboxyl ligands are well removed during device fabrication processes. Many efforts had been made to improve the PCE of PbS CQDs solar cells, including packing and passivation of CQDs [21, 22], adoption of new exchanging ligands [23], and design of new device structure [24]. (2015) 7(4):325331 or di-thiol were introduced during device fabrication process to remove the long-chain carboxyl acid ligands on the surface of PbS CQDs. The thin film prepared by this method was compact and showed good carrier mobility. Two kinds of solar cells based on PbS CQDs were fabricated to verify the effects of ligands passivation

Materials

Synthesis of PbS CQDs

Device Fabrication

Characterizations

Results and Discussion

A B Pb 4f