High-efficiency inverted polymer solar cells via dual effects of introducing the high boiling point solvent and the high conductive PEDOT:PSS layer

• Three types of device structures with the embedded Au NPs were investigated.
• ∼10% improvement of PCE was obtained by introducing a hcPEDOT:PSS layer in the devices.
• Further ∼10% increase of PCE was achieved by adding 1,8-diiodooctane in P3HT:PCBM.
• LVSEM and AFM were used to characterise morphologies of the active layers and Au NPs.

Polymer solar cells (PSCs) are of great interest in the past decade owing to their potentially low-cost in the manufacturing by the solution-based roll to roll method. In this paper, a novel inverted device structure was introduced by inserting a high conductive PEDOT:PSS (hcPEDOT:PSS) layer between the Au nanoparticles (NPs)-embedded hole transport layer (PEDOT:PSS) and the top electrode layer. Power conversion efficiency (PCE) initially reached up to 4.51%, illustrating ∼10% higher compared with the device similarly enhanced by Au NPs plasmonics where only one PEDOT:PSS layer with the embedded Au NPs was used in single bulk heterojunction inverted PSCs based on the poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methylester (P3HT:PCBM). The PCE was further improved from 4.51% to 5.01% by adding the high-boiling point solvent of 1,8-diiodooctane (DD) into the active layer, presenting ∼20% enhancement in PCE through dual effects of introducing the high boiling point solvent and the high conductive PEDOT:PSS layer. Morphologies of the active layers were characterised by SEM and AFM separately in the paper.

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