Manipulation of PEDOT:PSS with Polar and Nonpolar Solvent Post-treatment for Efficient Inverted Perovskite Solar Cells

Abstract

Poly(3,:poly(styrene sulfonate) (PEDOT:PSS) has been widely used as a hole-conducting polymer in many optoelectronic devices including perovskite solar cells. However, its electrical and surface properties are not well controlled during the conventional ambient annealing. Herein, we apply the solvent posttreatments, including toluene vapor annealing and ethylene glycol (EG) washing, to modify not only the electrical conductivity and work function but also, importantly, the surface composition and morphology of PEDOT:PSS thin films. We show that annealing PEDOT:PSS films in a nonpolar toluene vapor environment results in a slightly enhanced electrical conductivity and increased work function while maintaining the surface composition and morphology. The CH 3 NH 3 PbI 3 perovskite solar cells using the toluene vapor-annealed PEDOT:PSS hole transporting layers (HTLs) yield a 31.8% increase in power conversion efficiency (PCE) from the control devices with the ambient conditionannealed PEDOT:PSS HTLs. All photovoltaic parameters are increased because of reduced trap states at the perovskite/HTL interface, as well as efficient and balanced charge generation, transport, and extraction rates. In contrast, washing PEDOT:PSS films with the polar EG solvent removes the PSS on the surface, increases the surface roughness, and dramatically increases the electrical conductivity by 5 orders of magnitude but slightly decreases the work function. Consequently, the CH 3 NH 3 PbI 3 perovskite solar cells with EG-washed PEDOT:PSS HTLs result in a 28.6% decrease in PCE from the control devices because of the increased trap states at the perovskite/HTL interface, which leads to an inefficient hole extraction. The charge accumulation at the perovskite/HTL interface also reflects in a serious hysteresis of J−V curves in the reversed bias region. This work highlights the importance of controlling both electronic and surface properties of PEDOT:PSS HTLs for the improvement of perovskite solar cell performance.

Understanding the role of inorganic carrier transport layer materials and interfaces in emerging perovskite solar cells

“…552,553 Thus, to overcome these issues, PEDOT:PSS is either treated with a dimethylformamide (DMF)/methanol mixture or annealed with non-polar vapours of toluene, which improves its conductivity, reduces its trap state density, and facilitates smooth charge transfer at the PEDOT:PSS/perovskite interface, resulting in an improved PCE than the pristine HTL. 553,554 Separately, the development of a PEDOT:PSS toluene-based ink coated over the perovskite absorber in the conventional planar (n-i-p type) device architecture has attracted attention from the scientific and industrial community. 555 The absorbance of PEDOT films is very low in the UV-visible region, causing less parasitic losses during the second pass through the perovskite layer and resulting in an increased photocurrent with a PCE of 14.5% (Fig.…”

Metal-Free Transparent Three-Dimensional Flexible Electronics by Selective Molecular Bridges

“…The presence of polar solvents can induce PEDOT:PSS polymers to change from benzoid form to quinoid form, and it can also distract PSS molecules from the PEDOT structure to improve the PEDOT:PSS polymer conductivity. 74 As can be seen in Figure 2A, the sheet resistance of a PEDOT:PSS/PVA/PET film decreases with the increasing DMSO content in the operation. This DMSO treatment can reduce the sheet resistance >100 times lower than the original film when the concentration of DMSO is at 6 vol %.…”

“…To improve the conductivity of this PEDOT:PSS/PVA/PET film, an appropriate amount of dimethyl sulfoxide (DMSO) is introduced into the aqueous PEDOT:PSS colloidal solution before the polymer spin coating process. The presence of polar solvents can induce PEDOT:PSS polymers to change from benzoid form to quinoid form, and it can also distract PSS molecules from the PEDOT structure to improve the PEDOT:PSS polymer conductivity . As can be seen in Figure A, the sheet resistance of a PEDOT:PSS/PVA/PET film decreases with the increasing DMSO content in the operation.…”

Ambient Inkjet‐Printed High‐Efficiency Perovskite Solar Cells: Manipulating the Spreading and Crystallization Behaviors of Picoliter Perovskite Droplets

“…It is not only a good wetting surface for the perovskite precursor solution, but also a widely used HTM for the inverted PSC devices. [ 26,27 ] In this work, the PEDOT:PSS substrate were heated (heat‐assisted printing) to aid the crystallization of perovskite droplets against the ambient humidity. Although all printed films were immediately annealed at 100 °C for 10 min after the printing process, their morphology is various at different substrate (printing) temperatures ( Figure d).…”