Controlling the Polarity of Ag:PSS Polyelectrolyte Interfacial Layers in Organic Solar Cells

A critical factor affecting the efficiency of organic solar cells is the interfacial material between the electrode and the active layer. Developing interlayer systems whose electronic properties can be systematically tuned through simple compositional modification is attractive because it may enable more symmetric device architectures, simplified processing, and improved control of interfacial energetics. In this study, we prepared an interfacial control material by replacing p-doped poly-(3,4-ethylenedioxythiophene) (PEDOT) in the well-known hole-transporting material (HTM) PEDOT:poly-(styrenesulfonate) (PSS) with silver (Ag⁺ ions). Ag:PSS by itself was found to have insulating properties and did not yield compelling results as an HTM alone. However, we were able to control the polarity of Ag:PSS by mixing it with either PEDOT:PSS or poly-(ethylenimine) (PEI), enabling its use as both HTM and electron transport material (ETM), respectively. By employing p-type and n-type Ag:PSS, we achieved power conversion efficiencies of up to 8.482% with a PTB7:PC₇₁BM active layer. To analyze the effects on band structure, we used ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) to reveal systematic changes in energy bands that followed the interlayer composition. Our study demonstrates how compositional modification of Ag:PSS influences interfacial energetics and charge extraction behavior.