A Simple Cu(II) Polyelectrolyte as a Method to Increase the Work Function of Electrodes and Form Effective p‐Type Contacts in Perovskite Solar Cells

Abstract

One effective strategy to improve the performance of perovskite solar cells (PSCs) is to develop new hole transport layers (HTLs). In this work, a simple polyelectrolyte HTL, copper (II) poly(styrene sulfonate) (Cu:PSS), which comprises easily reduced Cu2+ counter‐ions with an anionic PSS polyelectrolyte backbone is investigated. Photoelectron spectroscopy reveals an increase in the work function of the anode and upward band bending effect upon incorporation of Cu:PSS in PSC devices. Cu:PSS shows a synergistic effect when mixed with polyethylenedioxythiophene: polystyrenesulfonate (PEDOT:PSS) in various proportions and results in a decrease in the acidity of PEDOT:PSS as well as reduced hysteresis in completed devices. Cu:PSS functions effectively as a HTL in PSCs, with device parameters comparable to PEDOT:PSS, while mixtures of Cu:PSS with PEDOT:PSS shows greatly improved performance compared to PEDOT:PSS alone. Optimized devices incorporating Cu:PSS/PEDOT:PSS mixtures show an improvement in efficiency from 14.35 to 19.44% using a simple CH3NH3PbI3 active layer in an inverted (P‐I‐N) geometry, which is one of the highest values yet reported for this type of device. It is expected that this type of HTL can be employed to create p‐type contacts and improve performance in other types of semiconducting devices as well.

Improving the Electrical Properties and Hole Extraction Efficiency of Inverted Perovskite Solar Cells with AuCl3 Interfacial Modification Layer

“…By introducing halide perovskite precursor to dope with PEDOT:PSS, Sandrez et al [ 28 ] improved the conductivity by two orders of magnitude compared to the adoption of PEDOT:PSS alone. Ali et al [ 29 ] used poly(II) copper sulfonate (Cu:PSS) to modify PEDOT:PSS and improved the efficiency of inverted PSCs from 14.35% to 19.44%. Xu et al [ 30 ] used PTB7 to adjust the energy orientation and hydrophobicity of PEDOT:PSS to form a better energy‐level matching and improved the hole mobility of PEDOT:PSS.…”

A pH‐Neutral Polyelectrolyte Hole Transport Layer for Improved Energy Band Structure at the Anode/PTB7 Junction and Improved Solar Cell Performance

“…These calculations suggest that highly transparent Cu:PSS based HTLs can improve light transmission to the active layer and increase the J SC of devices. [ 40 ] These results indicate that highly transparent PEDOT doped Cu:PSS may allow for superior light transmission and charge generation in PTB7:PC 71 BM solar cells as well.…”

“…It was determined that Cu:PSS layers alone are not thick enough to prevent back diffusion of electrons to the anode, allowing recombination to occur at the ITO electrode. [40] Whereas PEDOT:PSS has high conductivity and can be used to make thicker (>30 nm) films with a large number of doped charge carriers, Cu:PSS has low electrical conductivity and must be used in ultrathin layers (<10 nm), affecting only the interface of the active layer and allowing electrons to back diffuse through quantum tunneling. [42] For a deeper understanding of the J sc and FF results of the four optimized HTLs devices, shunt resistance (R sh ) and series resistance (R s ) were investigated by measuring the dark current of devices (Figure 2b).…”

“…In a previous study where Cu:PSS was investigated in the context of perovskite solar cells, two other sets of mixed HTLs were investigated in addition to neat PEDOT:PSS and Cu:PSS films. [ 40 ] Films consisting of Cu:PSS and mixtures with PEDOT:PSS were found to have smooth morphologies and to be highly transparent throughout the visible spectrum. In this work, two other sets of mixed HTLs were investigated in addition to neat PEDOT:PSS and Cu:PSS films.…”

“…We used this material alone, or as an admixture with PEDOT:PSS to improve the efficiency of devices by optimizing the ratio of Cu:PSS and PEDOT:PSS for use as efficient hole transport/electron blocking layers. [ 40 ] Using neat Cu:PSS as an HTL in OSC devices yielded performance that was comparable with PEDOT:PSS, while mixtures of Cu:PSS with PEDOT:PSS resulted in substantial improvements in PCE of up to 9.28 %. Devices using optimized Cu:PSS/PEDOT:PSS mixtures showed a 12% improvement in performance compared with PEDOT:PSS alone, with enhanced device stability under ambient conditions.…”