A Dopant‐Free Zwitterionic Conjugated Polyelectrolyte as a Hole‐Transporting and Interfacial Material for Perovskite Solar Cells

Abstract

Achieving rapid extraction and equivalent transport of charge carriers is an effective way to improve the performance of perovskite solar cells (PSCs). Herein, a thiophene‐based zwitterionic conjugated polyelectrolyte (poly(5‐amino‐5‐carboxy‐3‐oxapentyl)‐2,5‐thiophene [POWT]) is introduced into PSCs as a hole‐transporting and interfacial material. The polyelectrolyte has a high hole mobility of 5.74 × 10−3 cm2 V−1 s−1 (similar to that of poly(triarylamine) [PTAA]) and compatible covalence level relative to the perovskite. Terminated with a zwitterionic pair of a‐amino acid, POWT layer builds up a weak double‐layer capacitance at the interface, which is not strong enough to induce the migration of MA+ ions in the perovskite layer. Deep electrical study on the PSC with the structure of indium tin oxide (ITO)/POWT/FA0.2MA0.8PbI2.9Br0.1/C60/bathocuproine (BCP)/Ag discloses that the device has low carrier transfer resistance, low leakage current density, and minor interfacial charge accumulation. The open‐circuit voltage and the short‐circuit current density are much improved, and the power conversion efficiency (PCE) is up to 17.5%. With a‐amino acid zwitterions, POWT passivates the surface charge defects and grain boundaries of the perovskite film. The PSC presents negligible hysteresis and high stability. After 56 days, the unencapsulated PSC still remains at 85% of the original efficiency.

Dopant‐Free Ternary Conjugated Polymeric Hole‐Transporting Materials for Efficient Inverted Planar Perovskite Solar Cells

“…[47] In addition, the crystallization peaks of the perovskite film with a PDPPTBT underlayer are sharper, indicating that PDPPTBT can improve the crystallinity of perovskite, reduce the defects between grain boundaries, and facilitate the transport of carriers and stability. [48] As the thickness of the perovskite layer is almost the same for all the samples, the higher peak strength observed in the studied polymer HTMs may indicate the better crystallinity of perovskite, possibly due to its relatively nonpolar nature, [49] as exemplified by the contact angle analyses shown in Figure S10, Supporting Information. The estimated contact angles of PTPDTBT and PDPPTBT were found to be 65.2 and 65.8 , respectively, which were far superior to the conventional PEDOT:PSS (19.7 ).…”

Importance and Advancement of Modification Engineering in Perovskite Solar Cells

“…alignment was achieved at the perovskite/HTL/anode interface, with reduced energy offset and consequently enhanced V OC of 1.02 V, compared to 0.92 V for the control devices based on PEDOT:PSS HTL. [70] Figure 8. Chemical structures of MSAPBS, [53] 4-pyridinecarboxylic acid, [54] glycine, [55] creatine, [56] 1-butyl-3-methylimidazolium tetrafluoroborate, [57] JTCA, [58] TP6 [59] or TBAPF6, [99] PN6, [62] QAPDI, [64] HDAC, [65] FPyBr, [66] F-R-COOK, [67] π-PFE, [68] and POWT.…”

Increasing Stability of SnO2-Based Perovskite Solar Cells by Introducing an Anionic Conjugated Polyelectrolyte for Interfacial Adjustment

“…Ultraviolet photoelectron spectroscopy (UPS) measurements were conducted on an ultrahigh vacuum UPS system (Kratos Axis Supra) with a He Iα (21.2 eV) ultraviolet source. The cells were characterized as our report …”

“…A conjugated polyelectrolyte refers to a conjugated polymer with an ionic group (for example, a sulfonic acid group, a carboxyl group, and an ammonium group) on the side chain. In the past few years, several types of conjugated polyelectrolytes were introduced as ETL, HTL, or dopant in PSCs, achieving improved device performance with suppressed trap density and better charge extraction. − The ionic conjugated polymer electrolytes can form a strong interface dipole and may adjust the interface work function. − An anionic conjugated polyelectrolyte, a block copolymer polyfluorene (abbreviated to SPF), is composed of two fluorene monomers, one fluorene containing two sulfonic groups at the side chain and another containing two octyl side chains. SPF is both hydrophilic due to sulfonic groups and hydrophobic due to octyl chains.…”