Efficient Hole Extraction from Sb2S3 Heterojunction Solar Cells by the Solid Transfer of Preformed PEDOT:PSS Film

Abstract

Here, we report significant improvements of Voc and FF in Sb2S3 quantum dot (QD)-based, solid-state heterojunction solar cells prepared from the solid transfer of preformed PEDOT:PSS hole extraction layers. Despite the moderate optical properties of Sb2S3 QDs, the solid state QD solar cells suffer from poor power conversion efficiency (PCE) resulting from the disappointing Voc and the high series resistance since there is inefficient charge extraction from QDs to the metal top electrode. In order to improve the hole extraction performance, a significantly uniform PEDOT:PSS (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)) layer was transferred on the hole transport layer (P3HT, poly(3-hexylthiophene-2,5-diyl)) by using a simple solid-transfer method. In contrast with conventional spin-cast methods, the hydrophilic PEDOT:PSS layer was uniformly coated on the hydrophobic P3HT layer without any significant detriment to P3HT film properties. Due to improved contact surface for the Au top electrode and hole conductance resulting in significantly improved charge extraction, the power conversion efficiency was dramatically enhanced. Furthermore, the thickness of the PEDOT:PSS film was precisely optimized by layer-by-layer solid transfer, and thereby the PCE of the PEDOT:PSS solid-transfer device (30 nm) was improved by 25.7% in comparison to the PEDOT:PSS spin-cast device and by 76% in comparison to the PEDOT:PSS free device.