Conformational and Compositional Tuning of Phenanthrocarbazole-Based Dopant-Free Hole-Transport Polymers Boosting the Performance of Perovskite Solar Cells

Abstract

Conjugated polymers are regarded as promising candidates for dopant-free hole-transport materials (HTMs) in efficient and stable perovskite solar cells (PSCs). Thus far, the vast majority of polymeric HTMs feature structurally complicated benzo­[1,2-b:4,5-b’]­dithiophene (BDT) analogs and electron-withdrawing heterocycles, forming a strong donor–acceptor (D–A) structure. Herein, a new class of phenanthrocarbazole (PC)-based polymeric HTMs (PC1, PC2, and PC3) has been synthesized by inserting a PC unit into a polymeric thiophene or selenophene chain with the aim of enhancing the π–π stacking of adjacent polymer chains and also to efficiently interact with the perovskite surface through the broad and planar conjugated backbone of the PC. Suitable energy levels, excellent thermostability, and humidity resistivity together with remarkable photoelectric properties are obtained via meticulously tuning the conformation and elemental composition of the polymers. As a result, PSCs containing PC3 as dopant-free HTM show a stabilized power conversion efficiency (PCE) of 20.8% and significantly enhanced longevity, rendering one of the best types of PSCs based on dopant-free HTMs. Subsequent experimental and theoretical studies reveal that the planar conformation of the polymers contributes to an ordered and face-on stacking of the polymer chains. Furthermore, introduction of the “Lewis soft” selenium atom can passivate surface trap sites of perovskite films by Pb–Se interaction and facilitate the interfacial charge separation significantly. This work reveals the guiding principles for rational design of dopant-free polymeric HTMs and also inspires rational exploration of small molecular HTMs.

Vanadium Oxide‐Modified Triphenylamine‐Based Hole‐Transport Layer for Highly Reproducible and Efficient Inverted Perovskite Solar Cells

“…SCLC analysis was performed on a device structure of ITO/HTL/MAPbI 3 /MoO 3 /Al. Based on dark J – V curves, trap state density can be calculated by the following equation [ 14 ] where ε 0 is relative dielectric constant, ε is the vacuum permittivity, V TFL is the trap filling limited voltages, and L is the film thickness.…”

“…Recently, poly(triarylamine) (PTAA) is widely adopted as the HTL due to proper energy level alignment, related strong physicochemical interaction with perovskite, and mitigation of bulk defect activities, which shows relatively better device performance compared to other HTLs. [ 13,14 ] But, the reproducibility and fill factor (FF) of PTAA‐based PSCs is generally inferior due to the unsatisfactory perovskite growth in generating rough perovskite film with high charge recombination loss, originating from the grave hydrophobicity (contact angle > 90°) compared to 10°–30° for the hydrophilic perovskite films. [ 15,16 ] The wetting ability of HTLs is crucial for growing high‐quality perovskite films.…”

Intramolecular Electric Field Construction in Metal Phthalocyanine as Dopant‐Free Hole Transporting Material for Stable Perovskite Solar Cells with >21 % Efficiency

“…Metal phthalocyanines (MPcs) have attracted intense interest as HTMs in PSCs, due to the low preparation cost and excellent stability [29–31] . Their physical and chemical properties are also well‐adjusted by optimizing the central metal ions and the peripheral substituents in MPcs.…”

Efficient Inverted Perovskite Solar Cells with Low Voltage Loss Achieved by a Pyridine‐Based Dopant‐Free Polymer Semiconductor

“…In addition to introducing an additional passivation layer, directly endowing the HTLs with passivation functions should be a more efficient way to reduce the NRR in PVSCs, [30–32] since it can further simplify the device fabrication and avoid hindering charge transfer at the interface. Moreover, since the HTL is deposited before the perovskite layer in inverted devices, the HTL with passivation functions is expected to increase the interface contact and further to improve the crystal quality of perovskite films, leading to the decrease of NRR within the perovskite bulk.…”