Solution‐Processed Metal Ion Polyelectrolytes as Hole Transport Materials for Efficient Inverted Perovskite Solar Cells

Abstract

Despite achieving high efficiencies over a short time, further streamlining of hybrid lead‐halide perovskite solar cell (PSC) designs is necessary for their commercial viability. In this contribution, a new class of interfacial hole transporting layer (HTL) materials consisting of anionic polyelectrolytes comprising polystyrene sulfonate (PSS) with metal cations are explored. These materials represent alternatives to metal oxides, combining characteristics of metal oxides with the facile preparation and desirable film‐forming characteristics of polyelectrolytes. Polyelectrolytes with cations including Li, Mg, V, Mn, Co, Ni, Cu, Zn, Pd, Ag, In, Cs, and Pb as HTLs in inverted PSCs are explored. A range of positive and negative effects is observed for different metal cations, which are attributed to differences in the physical properties of the polyelectrolytes, and their influence on the electronic band structure of devices and the crystal qualities of the perovskite absorber. Ni and Cu polyelectrolytes created p‐type contacts at the anode of PSCs, improving device performance. These materials are believed to have potential in other types of devices as well. This type of metal:PSS polyelectrolyte has not yet been widely investigated, however, it is shown that it constitutes a simple and economic strategy to engineer energy band structures in perovskite devices.

Photoelectron Spectroscopic Study of the Interfacial Electronic Structures of Metal‐Ion Containing Polyelectrolytes on ITO Substrates

“…In a previous study, we reported IP values of ≈8 eV for thin films of all metal:PSS. [41] However, in this current study, the IP values for all metal:PSS are reported to be ≈7 eV, a difference which can be attributed to a difference in the reference WF of the ITO substrates. The UPS spectrum exhibited various changes attributed to E F alignment, which varied based on the film thickness and the type of metal.…”

“…Metal:PSS polyelectrolytes were synthesized according to previously reported procedures. [ 41 ] Solutions were prepared by dissolving metal:PSS materials in deionized water with an initial concentration of 10 mg/1 mL (1 wt.%) and performing serial dilution with a micropipette to vary the concentrations of the solutions to as low as 0.001% in order to vary the thickness of films upon spincoating. Metal:PSS films were deposited by spin‐coating the solutions at 2000 rpm for 60 s onto ITO substrates.…”

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

“…In contrast, the benchmark PEDOT:PSS HTL-based device shows relatively higher efficiency ( V OC = 0.85 V, J SC = 19.09 mA cm −2 , FF = 76.97% and PCE = 14.02%). Kang and coworkers developed an improved layer when a copper polyelectrolyte and PEDOT:PSS were mixed and used as an HTL between the active layer and the electrode, which showed improved characteristics compared to either material alone, 36 a result of reduced recombination loss and improved carrier extraction efficiency. To enhance the hole extraction ability of Ni:PSS, PEDOT:PSS was used in small quantities as an additive with Ni:PSS.…”

“…In a previous study, we investigated the general properties of a wide variety of metal:PSS polyelectrolytes (using various categories of metals, including period 4 transition metals, period 5 transition metals, alkali metals, and post-transition metals) including a screening of their effect on the current–voltage characteristics of perovskite solar solar cells. 36 Furthermore, electronic structure analyses were performed for all metals, revealing Cu:PSS and Ni:PSS as promising candidates for HTLs. Electronic structure analyses were performed for all metals, revealing Cu:PSS and Ni:PSS as promising candidates for HTLs.…”

Effect of GaN-Based Distributed Bragg Reflector on Optical Properties of CH3NH3PbBr3 Crystals

“…In 2009, Miyasaka prepared solar cells using hybrid perovskite materials (CH 3 NH 3 PbI 3 or CH 3 NH 3 PbBr 3 ) as the absorption layer for the first time, realizing a 3.81% photoelectric conversion efficiency (PCE) [4]. Since then, more and more research into hybrid perovskite-based solar cells has been reported and the PCE has increased continuously [5][6][7][8]. This is mainly because this kind of material has the characteristics of simple preparation, large carrier mobility, excellent light absorption ability and great chemical stability [9][10][11][12][13].…”