Molecular Regulation of Perylenediimide and Fluorene‐Based Cathode Interfacial Materials for Efficient Inverted Perovskite Solar Cells

Abstract

their high efficiency and low-cost solution manufacturing procedure and are considered the most likely to be commercialized and could be compared with silicon-based solar cells. The power conversion efficiencies (PCEs) of PSCs have increased dramatically from 3.8% to 25.7% [1][2][3] during the last decade with the advancements in fabrication techniques, [4][5][6] chemical compositions, [7,8] and phase stabilization techniques. [9,10] However, ion migration, electrode degradation, energy level mismatch, and poor interface contact are still the limited factors that needed to be considered and optimized. [11][12][13] Among them, interfacial contact defect is the most important challenge to be solved for the state-of-the-art PSCs. To this end, a lot of research have been done on interface engineering to reduce interface defects in order to higher photovoltaic performance of PSCs. [14,15] At present, the solution processed [6,6]-phenyl-C61-butyric acid methyl ester (PC 61 BM) is still used as benchmark electron transport material (ETM) in inverted PSCs because it can effectively passivate the charge trap states and defects on the surface of perovskite layer. [16,17] However, the PC 61 BM as ETL suffers from the larger energy level barrier with high-work function cathode (i.e., Ag) and leads to significant energy loss at PC 61 BM/Ag interface. Moreover, solution-processed PC 61 BM as cathode interface layer (CIL) also suffers from obvious aggregations with large roughness, leading to poor interface contact with Ag cathode and large charge recombination in PSCs.To correct the energy level mismatch and poor interface, an appropriate CIL need to be inserted between PC 61 BM and Ag electrode. [18,19] The CIL as a functional layer in PSC together with electron transport layer (ETL) plays the vital role of charge carrier extraction and transport, which can also modify the interfacial properties of ETL and lower the work function (WF) of the metal electrode. [20,21] Among cathode interface materials (CIMs), solution processable organic small molecules and polymers offer a more convenient device preparation process than alkaline salts (i.e., LiF) and metal oxides (i.e., ZnO, TiO 2 ), which normally require vacuum thermal evaporation or thermal annealing.In inverted perovskite solar cells (PSCs), n-doping fullerene electron transport layers (ETLs) have been found to prepare high efficiency devices due to their excellent performance in electrochemistry, film formability, and surface passivation. Herein, two cathode interface layers (CILs) 2PDI-FN and 2PDIT-FN are prepared with dimethylamino functional groups and PDI units. The addition of thiophene makes the 2PDIT-FN conjugated framework coplanar and enhances the effect of dimethylamino functional groups, which give 2PDIT-FN with higher electrical conductivity, electron mobility, self-doping property, and film formability. Moreover, dopant N-DMBI can further enhance these advantages of 2PDIT-FN. Consequently, a peak power conversion efficiency (PCE) of 20.44% is achieved with 2P...

Interface Engineering of Inverted Perovskite Solar Cells Using a Self‐doped Perylene Diimide Ionene Terpolymer as a Thickness‐Independent Cathode Interlayer†

“…When 10 wt% Bphen is added into the PNPDIN, 21.28% PCE is achieved, which is one of the best performances of PerSCs based on PDI CILs (Figure 1). [ 18,23‐37 ] More importantly, the high conductivity and good film morphology of PNPDIN also made the mixed CIL good thickness tolerance. The optimal PCE of the inverted PerSC still showed 20.46% for film thicknesses of up to 37 nm.…”

Inducing molecular orientation in solution-processed thin films of fluorene-bithiophene-based copolymer: thermal annealing vs. solvent additive

“…Fluorene-based copolymers are highly attractive organic semiconducting materials used for several optoelectronic applications, such as hole transport materials, 1–3 field-effect transistors, 4,5 light emitting devices 6–8 and electrochromic devices, 9,10 owing to their well-known synthetic route and chemical and thermal stability. In particular, the poly(9,9-dioctyl-fluorenyl- co -bithiophene) copolymer (F8T2 – chemical structure shown in Fig.…”

Dimensional Tuning of Perylene Diimide‐Based Polymers for Perovskite Solar Cells with Over 24% Efficiency

“…[23][24] The low-lying frontier molecular orbital makes PDI suitable as an electron-withdrawing unit to construct polymer semiconductor materials and tune their energy levels. [25][26] Moreover, the PDI molecule exhibits a large density of chemically active sites, for example, four carbonyl groups within the backbone, which could passivate the undercoordinated Pb 2+ on the surface of perovskite film through C≐O•••Pb 2+ noncovalent interactions. [27] However, the polymer interface materials based on PDI units have rarely been reported in the field of PSCs.…”