Efficient, Stable, and Low-Cost PbS Quantum Dot Solar Cells with Cr–Ag Electrodes

Jobeda J Khanam,Simon Y Foo,Pengsu Mao,Tianhan Liu,Zhibin Yu

doi:10.3390/nano9091205

Abstract

PbS quantum dots (QDs) are a promising nanostructured material for solar cells. However, limited works have been done to explore the active layer thickness, layer deposition techniques, stability improvement, and cost reduction for PbS QD solar cells. We address those issues of device fabrication herein and suggest their possible solutions. In our work, to get the maximum current density from a PbS QD solar cell, we estimated the optimized active layer thickness using Matlab simulation. After that, we fabricated a high-performance and low-cost QD photovoltaic (PV) device with the simulated optimized active layer thickness. We implemented this low-cost device using a 10 mg/mL PbS concentration. Here, spin coating and drop-cast layer deposition methods were used and compared. We found that the device prepared by the spin coating method was more efficient than that by the drop cast method. The spin-coated PbS QD solar cell provided 6.5% power conversion efficiency (PCE) for the AM1.5 light spectrum. Besides this, we observed that Cr (chromium) interfaced with the Ag (Cr–Ag) electrode can provide a highly air-stable electrode.

Highlights

The semiconductor quantum dots (QDs) of groups IV and VI make compounds PbSe and PbS
Colloidal QDs (CQDs) materials consist of individual QDs where the QDs remain side by side [17,18]
The film quality depends on the quantum dot size [20], the concentration of PbS QD material, ligand exchanger and exchanging time [15], an optimal annealing process [21], band alignment [22], and the solvent’s properties

Summary

Introduction

The semiconductor quantum dots (QDs) of groups IV and VI make compounds PbSe and PbS. The film quality depends on the quantum dot size [20], the concentration of PbS QD material, ligand exchanger and exchanging time [15], an optimal annealing process [21], band alignment [22], and the solvent’s properties. To explore the deposition method, we fabricated and compared the performance of PbS QD solar cells using drop cast and spin coating methodologies. We used 10 mg mL−1 PbS QDs instead of highly concentrated PbS QDs. To improve the air stability performance of the back electrode, we used a Cr–Ag electrode because the Cr layer provides excellent stability to silver and sticks well to the surface of the cell. Thin layers of Cr (5–10 nm) do not usually modify the properties of the devices [34,35]

Materials

Estimation of the PbS QD Layer Thickness

The Drop Cast Deposition Method for Device Fabrication

The Spin Coating Deposition Method for Device Fabrication

Device Characterization and Instrumentation

Results and Discussion