Nickel polyelectrolytes as hole transporting materials for organic and perovskite solar cell applications†

Engineering interfacial materials for use between the active layer and the electrodes in organic and perovskite solar cells is one of the most effective ways to increase device efficiency. Despite decades of development, new materials continue to emerge offering improved performance and streamlined fabrication of devices. Here, a hole transport layer (HTL) for organic and perovskite solar cells combining poly(styrene sulfonate) (PSS) and nickel (Ni²⁺) is presented. P-type carriers and p-doping at the anode are stabilized by the PSS backbone's negatively charged state. The impact of ionic moieties on the electronic band structure and characteristics of organic and perovskite solar cells must be understood. The combination of Nickel(II): poly(styrene sulfonate) (Ni:PSS) and poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) can improve efficiency to 15.67% (perovskite solar cell) and 16.90% (organic solar cell) over traditional Ni:PSS and PEDOT:PSS. Ultraviolet photoelectron spectroscopic observations at HTL/donor interfaces indicate energy level alignment, which is the cause of various changes in device performance. Low ionization potential (IP) and hole injection barrier (ϕ_h) are essential at the HTL/donor interface for effective charge extraction in organic and perovskite solar cells.