Novel Phenothiazine‐Based Self‐Assembled Monolayer as a Hole Selective Contact for Highly Efficient and Stable p‐i‐n Perovskite Solar Cells

Abstract

PSCs have two typical configurations, regular (n-i-p) and inverted (p-i-n). So far, the highest reported efficiencies of PSCs have been achieved using the n-i-p configuration with a mesoporous scaffold such as, a TiO 2 layer. [11] The mesoporous n-i-p structure usually requires a high temperature thermal treatment, exhibits severe hysteresis behavior and photo-induced degradation. The planar p-i-n architecture, which has no mesoporous scaffold, has attracted growing attention because it offers low temperature fabrication, much less pronounced hysteresis [12] and high stability with no need for dopants in the charge selective layer, which are known to cause degradation. [13] The p-i-n PSCs have also shown superior compatibility in perovskite based tandem solar cells due to lower parasitic absorption loss in the front contact. [14][15][16] Nevertheless, the maximum PCE of p-i-n PSCs still lags behind that of their n-i-p counterparts. This is predominantly the results of lower open circuit voltage and higher non-radiative recombination losses. [17] These losses are dominated by the interfaces of the charge-selective contacts. Extensive efforts have been devoted to improving these interfacial properties. For instance, approaches using ultrathin but conformal organic Recent advances in perovskite solar cells (PSCs) performance have been closely related to improved interfacial engineering and charge selective contacts. Here, a novel and cost-competitive phenothiazine based, self-assembled monolayer (SAM) as a hole-selective contact for p-i-n PSCs is introduced. The molecularly tailored SAM enables an energetically well-aligned interface with the perovskite absorber, with minimized nonradiative interfacial recombination loss, thus dramatically improving charge extraction/transport and device performance. The resulting PSCs exhibit a power conversion efficiency (PCE) of up to 22.44% (certified 21.81%) with an average fill factor close to 81%, which is among the highest efficiencies reported to date for p-i-n PSCs. The new SAM also demonstrates the outstanding operational stability of the PSC, with increasing PCE from 20.3% to 21.8% during continuous maximum power point tracking under a simulated 1 sun illumination for 100 h. The reported findings highlight the great potential of engineered SAMs for the fabrication of stable and high performing PSCs.

Self-assembled monolayer enabling improved buried interfaces in blade-coated perovskite solar cells for high efficiency and stability

“…Recently, self-assembled monolayer (SAM) has been introduced as hole-extraction layer (HEL) for small-area PVSCs with high photovoltaic performance [20][21][22][23]. SAMs are ordered arrays of organic molecules which contain an anchoring group bonding to the substrate surface, a linkage determining the packing, and a functional headgroup tuning its surface properties.…”

Extended phenothiazines: synthesis, photophysical and redox properties, and efficient photocatalytic oxidative coupling of amines

“…3–5 Also, because phenothiazine derivatives exhibit low oxidation potentials with a fully reversible one-electron redox process and good hole mobility, they have been widely employed as efficient hole transport materials (HTMs) for perovskite solar cells (PSCs). 6–8 In addition, phenothiazine is a very unique luminophore that can display conventional fluorescence and thermally activated delayed fluorescence (TADF) as well as room-temperature phosphorescence (RTP), mainly because of its distinct boat conformation that can induce different charge transfer characteristics and molecular packing motifs. 9–15 Moreover, phenothiazine derivatives have also been proven to be effective photoredox catalysts for various synthetic transformations ranging from metal-free atom transfer radical polymerization (ATRP) for controlled polymer synthesis 16–23 to small molecule transformations such as radical dehalogenations, 24 nucleophilic alkoxylations of alkyl olefins, 25 photoredox catalyzed C–N and C–H/C–H cross-couplings, 26,27 and so on.…”

Conjugated Self-Assembled Monolayer as Stable Hole-Selective Contact for Inverted Perovskite Solar Cells

“…22 Figures 1a and S1 depict molecular structures of reported highperformance SAM based HSCs, most of which (especially the well-established PACz series) feature an alkyl based linker. 16,17,19,23,24 The nonconjugated molecular structures are unfavorable for stability of electron-rich arylamine moieties, as well as charge-transport capability, due to the localization of electrons and charges. 25 In this work, we report a series of conjugated SAM-based HSCs for enhancing intrinsic photo-and electrical stability without sacrifice of photovoltaic performance.…”

“…Among various types of HSCs for inverted-structured PSCs, the anchoring-based self-assembled monolayer (SAM) paradigm has recently outperformed traditional HTMs based on PEDOT:PSS, polymeric arylamine, or inorganic p-type semiconductors like nickel oxides in terms of power conversion efficiencies (PCEs). − Moreover, the SAM based HSCs have unique advantages of minimal parasitic absorption, low material consumption, and simplified fabrication for large-area PSCs. The molecular structure of SAM based HSCs typically consists of an arylamine based hole-transporting head, an anchoring group like carboxylic acid (-COOH) or phosphonic acid (-PO­(OH) 2 ) that can chemically adsorb onto the surface of the transparent conductive oxide (such as indium tin oxide, ITO), and a linker between them to assist self-assembly …”

“…The molecular structure of SAM based HSCs typically consists of an arylamine based hole-transporting head, an anchoring group like carboxylic acid (-COOH) or phosphonic acid (-PO­(OH) 2 ) that can chemically adsorb onto the surface of the transparent conductive oxide (such as indium tin oxide, ITO), and a linker between them to assist self-assembly Figures a and S1 depict molecular structures of reported high-performance SAM based HSCs, most of which (especially the well-established PACz series) feature an alkyl based linker. ,,,, The nonconjugated molecular structures are unfavorable for stability of electron-rich arylamine moieties, as well as charge-transport capability, due to the localization of electrons and charges …”