Interfacial Layer Materials with a Truxene Core for Dopant-Free NiOx -Based Inverted Perovskite Solar Cells.

Nickel oxide (NiOx ) is commonly used as a holetransporting material (HTM) in p-i-n perovskite solar cells. However, the weak chemical interaction between the NiOx and CH3 NH3 PbI3 (MAPbI3 ) interface results in poor crystallinity, ineffective hole extraction, and enhanced carrier recombination, which are the leading causes for the limited stability and power conversion efficiency (PCE). Herein, two HTMs, TRUX-D1 (N2 ,N7 ,N12 -tris(9,9-dimethyl-9H-fluoren-2-yl)-5,5,10,10,15,15-hexaheptyl-N2 ,N7 ,N12 -tris(4-methoxyphenyl)-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene-2,7,12-triamine) and TRUX-D2 (5,5,10,10,15,15-hexaheptyl-N2 ,N7 ,N12 -tris(4-methoxyphenyl)-N2 ,N7 ,N12 -tris(10-methyl-10H-phenothiazin-3-yl)-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene-2,7,12-triamine), are designed with a rigid planar C3 symmetry truxene core integrated with electron-donating amino groups at peripheral positions. The TRUX-D molecules are employed as effective interfacial layer (IFL) materials between the NiOx and MAPbI3 interface. The incorporation of truxene-based IFLs improves the quality of perovskite crystallinity, minimizes nonradiative recombination, and accelerates charge extraction which has been confirmed by various characterization techniques. As a result, the TRUX-D1 exhibits a maximum PCE of up to 20.8% with an impressive long-term stability. The unencapsulated device retains 98% of their initial performance following 210 days of aging in a glove box and 75.5% for the device after 80 days under ambient air condition with humidity over 40% at 25 °C.

Commercially available jeffamine additives for p-i-n perovskite solar cells.

Commercially available Jeffamines (polyetheramine) with average molecular weights of 2000 and 3000 g mol-1; one (M2005), two (D2000), and three (T3000) primary amino groups end-capping on the polyether backbone; and propylene oxide (PO) and ethylene oxide (EO) functionality were explored as additives for application in MAPbI3 perovskite solar cells (PSCs). The results indicated that the embedding of Jeffamine additives effectively passivates the defects in the grain boundaries of perovskite through the coordination bonding between the nitrogen atom and the uncoordinated lead ion of perovskite. We fabricated p-i-n PSC devices with the structure of glass/indium tin oxide (ITO)/NiOx/CH3NH3PbI3 (with and without Jeffamine)/PC61BM/BCP/Ag. We observed the interaction between the Jeffamine and perovskites. This interaction led to increased lifetimes of the carriers of perovskite, which enabled the construction of high-performance p-i-n PSCs. For the Jeffamine-D2000-derived device, we observed an increase in the power conversion efficiency from 14.5% to 16.8% relative to the control device. Furthermore, the mechanical properties of the perovskite films were studied. The interaction between the additive and perovskite reinforced the flexibility of the thin film, which may pave the way for stretchable optoelectronics.

Defect Passivation by Amide-Based Hole-Transporting Interfacial Layer Enhanced Perovskite Grain Growth for Efficient p-i-n Perovskite Solar Cells.

In this study, we synthesized four acceptor-donor-acceptor type hole-transporting materials (HTMs) of SY1-SY4 for an HTMs/interfacial layer with carbazole as the core moiety and ester/amide as the acceptor unit. These HTMs contain 4-hexyloxyphenyl substituents on the carbazole N atom, with extended π-conjugation achieved through phenylene and thiophene units at the 3,6-positions of the carbazole. When using amide-based HTMs SY2 as a dopant-free HTM in a p-i-n perovskite solar cell (PSC), we achieved a power conversion efficiency (PCE) of 13.59% under AM 1.5G conditions (100 mW cm-2); this PCE was comparable with that obtained when using PEDOT:PSS as the HTM (12.33%). Amide-based SY2 and SY4 HTMs showed a larger perovskite grain than SY1 and SY3 because of the passivation of traps/defects at the grain boundaries and stronger interaction with the perovskite layer. In further investigation, we demonstrated highly efficient and stable PSCs when using the dopant-free p-i-n device structure indium tin oxide/NiOx/interfacial layer (SY-HTMs)/perovskite/PC61BM/BCP/Ag. The interfacial layer improved the PCEs and large grain size (micrometer scale) of the perovskite layer because of defect passivation and interface modification; the amide group exhibited a Lewis base adduct property coordinated to Ni and Pb ions in NiOx and perovskite, bifacial defect passivation and reduced the grain boundaries to improve the crystallinity of the perovskite. The amide-based SY2 exhibited the stronger interaction with the perovskite layer than that of ester-based SY1, which is related to the observations in X-ray absorption near edge structure (XANES). The best performance of the NiOx/SY2 device was characterized by a short-circuit current density (Jsc) of 21.76 mA cm-2, an open-circuit voltage (Voc) of 1.102 V, and a fill factor of 79.1%, corresponding to an overall PCE of 18.96%. The stability test of the PCE of the NiOx/SY2 PSC device PCE showed a decay of only 5.01% after 168 h; it retained 92.01% of its original PCE after 1000 h in Ar atmosphere. Time-resolved photoluminescence spectra of the perovskite films suggested that the hole extraction capabilities of the NiOx/SY-HTMs were better than that of the bare NiOx. The superior film morphologies of the NiOx/SY-HTMs were responsible for the performances of their devices being comparable with those of bare NiOx-based PSCs. The photophysical properties of the HTMs were analyzed through time-dependent density functional theory with the B3LYP functional.

Embedding a Diketopyrrolopyrrole-Based Cross-linking Interfacial Layer Enhances the Performance of Organic Photovoltaics.

In this study, we prepared DPPBTDA, a diketopyrrolopyrrole-based small molecule presenting a terminal cross-linkable azido group, as a cathode modifying layer for organic photovoltaics (OPVs) having the inverted device structure glass/indium tin oxide/zinc oxide (ZnO) with or without the interfacial layer (IFL)/active layer/MoO3/Ag. The active layer comprising a blend of poly[4,8-bis(5-(2-ethylhexyl)thien-2-yl)benzo[1,2- b;4,5- b']dithiophene-2,6-diyl- alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4- b]thiophene)-2-carboxylate-2,6-diyl] (PTB7-Th) as the electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor. Atomic force microscopy, space-charge-limited current mobility, surface energy, electron spectroscopy for chemical analysis depth profile, ultraviolet photoelectron spectroscopy analysis, and OPV performance data revealed that the surface status of ZnO changed after inserting the DPPBTDA/PCBM hybrid IFL and induced an optimized blend morphology, having a preferred gradient distribution of the conjugated polymer and PC71BM, for efficient carrier transport. The power conversion efficiency (AM 1.5 G, 1000 W m-2) of the device incorporating the hybrid IFL increased to 9.4 ± 0.11% from 8.5 ± 0.15% for the preoptimized PTB7-Th/PCBM device (primarily because of an enhancement in the fill factor from 68.7 ± 1.1 to 72.1 ± 0.8%).

Perovskite photovoltaics featuring solution-processable TiO2 as an interfacial electron-transporting layer display to improve performance and stability.

In this study we used solution-processable crystalline TiO2 nanoparticles as an interfacial modified layer between the active layer and aluminum cathode to fabricate CH3NH3PbI3/PCBM-based planar heterojunction perovskite photovoltaic (PPV) devices. We optimized the performance of the PPV device prepared without TiO2 by varying the preheating temperature of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT) substrate, obtaining a power conversion efficiency (PCE) of 6.3% under simulated AM 1.5 G irradiation (100 mW cm(-2)). After incorporating the TiO2 layer, we obtained a much higher PCE of 7.0%. The TiO2-containing PPV device exhibited extremely high stability (retaining ∼96% of its PCE after 1000 h) under long-term storage in a dark N2-filled glove box; the unencapsulated device retained approximately 80% of its original efficiency (T80) after 1 week under ambient conditions (ISOS-D-1; defined as 23 °C/50% RH). In contrast, the normal device was sensitive to ambient conditions with a value of T80 at only 3 h. We attributed the improved device performance (PCE, stability) to the enhanced electron transporting, hole blocking, and barrier properties arising from the presence of the TiO2 layer.

Two-step thermal annealing improves the morphology of spin-coated films for highly efficient perovskite hybrid photovoltaics.

In this paper, we describe relationships between the morphologies and the power conversion efficiencies (PCE) of perovskite photovoltaics having a conventional p-i-n heterojunction structure, indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS)/CH(3)NH(3)PbI(3-x)Cl(x)/PC(61)BM/Al. The PCE of such a device is highly dependent on the morphology of the perovskite film, which is governed by the concentrations of its precursors and the annealing conditions. A two-step annealing process allowed sufficient crystallization of the perovskite material, with a high coverage at a high precursor concentration. Relative to the device prepared using a one-step process (90 °C for 30 min), we observed a 60% increase in PCE for this optimized device. The corresponding devices exhibited extremely high stability after long-term storage (>1368 h) in the dark in a N2-filled glove box, with consistently high PCEs (AM 1.5 G, 100 mW cm(-2)) of up to 9.1%.

Increasing the open-circuit voltage in high-performance organic photovoltaic devices through conformational twisting of an indacenodithiophene-based conjugated polymer.

A fused ladder indacenodithiophene (IDT)-based donor-acceptor (D-A)-type alternating conjugated polymer, PIDTHT-BT, presenting n-hexylthiophene conjugated side chains is prepared. By extending the degree of intramolecular repulsion through the conjugated side chain moieties, an energy level for the highest occupied molecular orbital (HOMO) of -5.46 eV--a value approximately 0.27 eV lower than that of its counterpart PIDTDT-BT--is obtained, subsequently providing a fabricated solar cell with a high open-circuit voltage of approximately 0.947 V. The hole mobility (determined using the space charge-limited current model) in a blend film containing 20 wt% PIDTHT-BT) and 80 wt% [6,6]-phenyl-C71 butyric acid methyl ester (PC71 BM) is 2.2 × 10(-9) m(2) V(-1) s(-1), which is within the range of reasonable values for applications in organic photovoltaics. The power conversion efficiency is 4.5% under simulated solar illumination (AM 1.5G, 100 mW cm(-2)).