Polymer/Fullerene Blend Solar Cells with Cadmium Sulfide Thin Film as an Alternative Hole-Blocking Layer.

Murugathas Thanihaichelvan,Dhayalan Velauthapillai,Kailasapathy Balashangar,Selvadurai Loheeswaran,Punniamoorthy Ravirajan

doi:10.3390/polym11030460

Murugathas Thanihaichelvan, Dhayalan Velauthapillai + Show 3 more

Open Access

https://doi.org/10.3390/polym11030460

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Abstract

In this work, chemical bath-deposited cadmium sulfide (CdS) thin films were employed as an alternative hole-blocking layer for inverted poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction solar cells. CdS films were deposited by chemical bath deposition and their thicknesses were successfully controlled by tailoring the deposition time. The influence of the CdS layer thickness on the performance of P3HT:PCBM solar cells was systematically studied. The short circuit current densities and power conversion efficiencies of P3HT:PCBM solar cells strongly increased until the thickness of the CdS layer was increased to ~70 nm. This was attributed to the suppression of the interfacial charge recombination by the CdS layer, which is consistent with the lower dark current found with the increased CdS layer thickness. A further increase of the CdS layer thickness resulted in a lower short circuit current density due to strong absorption of the CdS layer as evidenced by UV-Vis optical studies. Both the fill factor and open circuit voltage of the solar cells with a CdS layer thickness less than ~50 nm were comparatively lower, and this could be attributed to the effect of pin holes in the CdS film, which reduces the series resistance and increases the charge recombination. Under AM 1.5 illumination (100 mW/cm2) conditions, the optimized PCBM:P3HT solar cells with a chemical bath deposited a CdS layer of thickness 70 nm and showed 50% power conversion efficiency enhancement, in comparison with similar solar cells with optimized dense TiO2 of 50 nm thickness prepared by spray pyrolysis.

Highlights

Organic bulk heterojunction solar cells have attracted significant attention due to their potential to fabricate flexible and cost efficient solar cells [1]
We focused on a simple chemical bath deposition method for fabricating the cadmium sulfide (CdS)
CdS films within deposition time of in Figure 2a.47The were measured at fiveasdifferent points and52.3 the±error barsnm), represents the min.thicknesses

Summary

Introduction

Organic bulk heterojunction solar cells have attracted significant attention due to their potential to fabricate flexible and cost efficient solar cells [1]. Recent works reported that the efficiency has gone beyond the 10% mark with non-fullerene acceptors and high hole mobility polymers with multiple layers of donor acceptor composites [2,3,4]. The bulk heterojunction (BHJ) blend structure resolves the limitations of polymers, such as low diffusion lengths and low mobility, by providing interpenetrating donor–acceptor networks [5,6,7]. The most general structures used in high efficiency BHJ solar cells are transparent conducting oxide (TCO), electron-blocking layer (EBL), donor–acceptor blend/hole-blocking layer (HBL), and metal electrodes. Polymers 2019, 11, 460 known as a hole- blocking layer (HBL) in these types of cells. The poor stability of PEDOT: PSS in an ambient atmosphere makes the conventional cell structure with PEDOT:PSS as HBL unstable [8]

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