Improved Efficiency and Stability in 1,5-Diaminonaphthalene Iodide-Passivated 2D/3D Perovskite Solar Cells.

Engineering multidimensional two-dimensional/three-dimensional (2D/3D) perovskite interfaces as light harvesters has recently emerged as a potential strategy to obtain a higher photovoltaic performance in perovskite solar cells (PSCs) with enhanced environmental stability. In this study, we utilized the 1,5-diammonium naphthalene iodide (NDAI) bulky organic spacer for interface modification in 3D perovskites for passivating the anionic iodide/uncoordinated Pb2+ vacancies as well as facilitating charge carrier transfer by improving the energy band alignment at the perovskite/HTL interface. Consequently, the NDAI-treated 2D/3D PSCs showed an enhanced open-circuit voltage and fill factor with a remarkable power conversion efficiency (PCE) of 21.48%. In addition, 2D/3D perovskite devices without encapsulation exhibit a 77% retention of their initial output after 1000 h of aging under 50 ± 5% relative humidity. Furthermore, even after 200 h of storage in 85 °C thermal stress, the devices maintain 60% of their initial PCE. The defect passivation and interface modification mechanism were studied in detail by UV vis absorption, photoluminescence spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), solid-state NMR, space-charge-limited current (SCLC) mobility measurement, and impedance spectroscopy. This study provides a promising path for perovskite surface modification in slowing their degradation against external stimuli, providing a future direction for increasing the perovskite device efficiency and durability.

Interplay of Kinetic and Thermodynamic Reaction Control Explains Incorporation of Dimethylammonium Iodide into CsPbI3.

CsPbI3 is a promising material for optoelectronics owing to its thermal robustness and favorable bandgap. However, its fabrication is challenging because its photoactive phase is thermodynamically unstable at room temperature. Adding dimethylammonium (DMA) alleviates this instability and is currently understood to result in the formation of DMA x Cs1-x PbI3 perovskite solid solutions. Here, we use NMR of the 133Cs and 13C local structural probes to show that these solid solutions are not thermodynamically stable, and their synthesis under thermodynamic control leads to a segregated mixture of yellow one-dimensional DMAPbI3 phase and δ-CsPbI3. We show that mixed-cation DMA x Cs1-x PbI3 perovskite phases only form when they are kinetically trapped by rapid antisolvent-induced crystallization. We explore the energetics of DMA incorporation into CsPbI3 using first-principles calculations and molecular dynamics simulations and find that this process is energetically unfavorable. Our results provide a complete atomic-level picture of the mechanism of DMA-induced stabilization of the black perovskite phase of CsPbI3 and shed new light on this deceptively simple material.

Highly Efficient and Stable 2D Dion Jacobson/3D Perovskite Heterojunction Solar Cells.

Heterostructures involving two-dimensional/three-dimensional (2D/3D) perovskites have recently attracted increased attention due to their ability to combine the high photovoltaic performance of 3D perovskites with the increased stability of 2D perovskites. Here we report ammonium thiocyanate (NH4SCN) passivated 3D methylammonium lead triiodide (MAPbI3) perovskite active layer and deposition of 2D perovskite capping layer using xylylene diammonium iodide (XDAI) organic cation. The 2D/3D perovskite heterojunction formation is probed by using FESEM and UPS spectroscopy. The NH4SCN passivated MAPbI3 perovskite has shown 19.6% PCE compared to the 17.18% PCE of pristine MAPbI3 perovskite solar cells (PSCs). Finally, the champion 2D/3D perovskite heterojunction based solar cells have achieved the remarkable PCE of 20.74%. The increased PCE in 2D/3D PSCs is mainly attributed to the reduced defect density and suppressed nonradiative recombination losses. Moreover, the hydrophobic 2D capping layer endows the 2D/3D heterojunction perovskites with exceptional moisture, thermal and UV stability, highlighting the promise of highly stable and efficient 2D/3D PSCs.

Thiocyanate-Passivated Diaminonaphthalene-Incorporated Dion-Jacobson Perovskite for Highly Efficient and Stable Solar Cells.

Two-dimensional (2D) metal halide perovskites have recently emerged as promising photovoltaic materials due to their superior ambient stability and rich structural diversity. However, power conversion efficiencies (PCEs) of the 2D perovskites solar cells (PSCs) still lag behind their three-dimensional (3D) counterpart, particularly due to the anisotropy in the charge carrier mobility and inhomogeneous energy landscape. A promising alternative is Dion-Jacobson (D-J) phase quasi-2D perovskite, where the bulky organic diammonium cations are introduced into inorganic frameworks to remove the weak van der Waals interactions between interlayers and to improve the open-circuit voltage (Voc). Although the D-J phase 2D perovskite shows a homogeneous energy landscape and better charge transport, their poor crystallinity and existence of higher trap states remain a major challenge for the development of high-efficiency solar cells device. To address this issue, here, we report the eclipsed D-J phase 2D perovskite using 1,5-diaminonaphthalene cation and subsequently treated the film with ammonium thiocyanate (NH4SCN) additive to further improve the film crystallinity, out-of-plane orientation, and carrier mobility. We observe that 2 mol NH4SCN surface treatment in NDA-based D-J phase perovskite leads to better film morphology and improved crystallinity, as confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Time-resolved photoluminescence (TRPL) spectroscopy and steady-state space charge limited current (SCLC) mobility measurement reveal a significant reduction of trap-assisted nonradiative recombination and improvement of carrier mobility in the thiocyanate-passivated perovskite. Consequently, the PCE of the NH4SCN-treated (NDA)(MA)3(Pb)4(I)13 perovskite device enhanced nearly 46% from 10.3 to 15.08%. We have further studied intensity-dependent J-V characteristics, which demonstrate the reduction of ideality factor, confirming the effective suppression of trap-assisted nonradiative recombination, consistent with the transient PL results. Electrochemical impedance spectroscopy (EIS) confirms the improved charge carrier transport in NH4SCN additive-treated devices. Interestingly, our additive-engineered unsealed perovskite devices retained 75% of their initial efficiency after 1000 h of continuous storage under 60% relative humidity. This study opens up the strategy for developing high-efficiency and stable 2D perovskite solar cells.

Azahomofullerenes as New n-Type Acceptor Materials for Efficient and Stable Inverted Planar Perovskite Solar Cells.

Fullerene derivatives with a strong electron-accepting ability play a crucial role in enhancing both the performance and stability of perovskite solar cells (PSCs). However, most of the used fullerene molecules are based on [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which limits the device performance due to difficulties in preparing high-quality and uniform thin films. Herein, solution-processable azahomofullerene (AHF) derivatives (abbreviated as AHF-1 and AHF-2) are reported as novel and effective electron-transport layers (ETLs) in p-i-n planar PSCs. Compared to the control PCBM ETL-based PSCs, the devices based on AHFs exhibit higher photovoltaic performances, which is attributed to the enhanced charge-transport properties and improved layer morphology leading to a maximum power conversion efficiency (PCE) of 20.21% in the case of the device based on AHF-2 ETL. Besides, due to the preferable energy band alignment with the perovskite layer, reduced trap states, and suppressed charge recombination, the device with AHF-2 ETL exhibits significantly suppressed hysteresis and improved stability under both ambient and thermal conditions.

Atomic Layer Deposition of an Effective Interface Layer of TiN for Efficient and Hysteresis-Free Mesoscopic Perovskite Solar Cells.

Perovskite solar cells (PSCs) have experienced outstanding advances in power conversion efficiencies (PCEs) by employing new electron transport layers (ETLs), interface engineering, optimizing perovskite morphology, and improving charge collection efficiency. In this work, we study the role of a new ultrathin interface layer of titanium nitride (TiN) conformally deposited on a mesoporous TiO2 (mp-TiO2) scaffold using the atomic layer deposition method. Our characterization results revealed that the presence of TiN at the ETL/perovskite interface improves the charge collection as well as reduces the interface recombination. We find that the morphology (grain size) and optical properties of the perovskite film deposited on the optimized mp-TiO2/TiN ETL are improved drastically, leading to devices with a maximum PCE of 19.38% and a high open-circuit voltage (Voc) of 1.148 V with negligible hysteresis and improved environmental (∼40% RH) and thermal (80 °C) stabilities.