High‐Mobility p‐Type Organic Semiconducting Interlayer Enhancing Efficiency and Stability of Perovskite Solar Cells

Abstract

A high‐mobility p‐type organic semiconductor based on benzodithiophene and diketopyrrolopyrrole with linear alkylthio substituents (BDTS‐2DPP) is used as a dual function interfacial layer to modify the interface of perovskite/2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene in planar perovskite solar cells. The BDTS‐2DPP layer can remarkably passivate the surface defects of perovskite through the formation of Lewis adduct between the under‐coordinated Pb atoms in perovskite and S atoms in BDTS‐2DPP, and also shows efficient hole extraction and transfer properties. The devices with BDTS‐2DPP interlayer show a peak power conversion efficiency of 18.2%, which is higher than that of reference devices without the BDTS‐2DPP interlayer (16.9%). Moreover, the hydrophobic BDTS‐2DPP interlayer effectively protects the perovskite against moisture, leading to enhanced device stability.

Reducing Detrimental Defects for High‐Performance Metal Halide Perovskite Solar Cells

“…[4,5,34a] Thes urface under-coordinated Pb 2+ (Figure 1b and Figure 5a-c) is the main source of trap states and several chemicals have been proposed to heal this particular type of defect. As election of organic molecules containing Lewis base functional groups,s uch as pyridine, [64,70] thiophene, [64] thiourea, [71] 6,6,12,12-tetrakis(4-hex-ylphenyl)-indacenobis-(dithieno[3,2-b;2,3-d]thiophene) end-capped with 1,1-dicyanomethylene-3-indanone units with 0t o2fluorine substituents (INIC), [72] perylene diimide and dithienothiophene (PPDIDTT), [73] benzodithiophene and diketopyrrolopyrrole with linear alkylthio substituents (BDTS-2DPP), [74] 1,3,4thiadiazolidine-2,5-dithione (TDZDT), [75] organic semiconducting non-fullerene acceptor molecule named IT-M, [76] 3,9bis(2-meth-ylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(5-hexylthienyl)-dithieno[2,3-d:2',3'-d']-sindaceno[1,2-b:5,6-b']dithiophene (ITIC-Th), [77] 2-(6-bromo-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)ethan-1-ammonium iodide (2-NAM), [78] and others [79] were employed. Lewis base can coordinate with Pb 2+ through lone pair electrons neutralizing its positive charge leading to subsequent annihilation of electronic trap states.T hese passivation treatments often result in significant enhancement in photoluminescence quantum yield (PLQY) and longer-lived excited charge carrier lifetime in perovskites often interpreted as decrease of non-radiative recombination centers.I na ddition, ab lue shift in the PL peak after the perovskite passivation is indicative of suppressed radiative recombination between charge traps.…”

“…The surface under‐coordinated Pb 2+ (Figure b and Figure a–c) is the main source of trap states and several chemicals have been proposed to heal this particular type of defect. A selection of organic molecules containing Lewis base functional groups, such as pyridine, thiophene, thiourea, 6,6,12,12‐tetrakis(4‐hex‐ylphenyl)‐indacenobis(dithieno[3,2‐b;2,3‐d]thiophene) end‐capped with 1,1‐dicyanomethylene‐3‐indanone units with 0 to 2 fluorine substituents (INIC), perylene diimide and dithienothiophene (PPDIDTT), benzodithiophene and diketopyrrolopyrrole with linear alkylthio substituents (BDTS‐2DPP), 1,3,4‐thiadiazolidine‐2,5‐dithione (TDZDT), organic semiconducting non‐fullerene acceptor molecule named IT‐M, 3,9‐bis(2‐meth‐ ylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(5‐hexylthienyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′] dithiophene (ITIC‐Th), 2‐(6‐bromo‐1,3‐dioxo‐1H‐benzo[de]isoquinolin‐2(3H)‐yl)ethan‐1‐ammonium iodide (2‐NAM), and others were employed. Lewis base can coordinate with Pb 2+ through lone pair electrons neutralizing its positive charge leading to subsequent annihilation of electronic trap states.…”

Intensive Exposure of Functional Rings of a Polymeric Hole‐Transporting Material Enables Efficient Perovskite Solar Cells

“…In addition to these bulk properties of charge‐transporting layer, the interface between the charge‐transporting material and the perovskite layer is also of great significance for the PSC device performance. So far, various self‐assembly monolayers or ionic liquids have been applied to modify the interfaces between metal oxide film and its upper perovskite layer, and small molecules or polymers have been directed to tuning the interfaces between the perovskite layer and its upper charge‐transporting layer. These always led to less recombination centers through passivating the defects on the surface and/or in the bulk of perovskite layer or to a higher charge‐extracting ability due to a stronger interaction or a dipole moment across the interfaces, and resulted in a markedly increased PCE.…”

Side‐Chain Engineering on Dopant‐Free Hole‐Transporting Polymers toward Highly Efficient Perovskite Solar Cells (20.19%)

“…Previously, designing of HTMs was mainly focused on the bulky properties of the HTM layer, especially the hole mobilities, and consequently the well‐known face‐on molecular orientation where the plane of polymer's main chain is parallel or intermolecular π–π stacking direction is perpendicular to the substrate was widely adopted as a criterion when one designs an HTM . Later, the interfaces between the perovskite and HTM layer were paid attention to be modified by small molecules and polymers, so that the defects on the surface and/or in the bulk of the perovskite layer could be passivated, leading to an enhanced photovoltaic performance. Nowadays, researchers have gradually recognized that the interaction between the perovskite layer and the HTM is also very crucial, and this interaction now turns to be an important designing factor for the HTMs.…”