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The interface between the electron transport layer (ETL) and the perovskite film plays a vital role in the performance of perovskite solar cells (PSCs). Here, (2-hydroxyethyl)amine hydroiodide (EOAI) is employed to regulate the interface properties at the SnO2/perovskite. The –NH3+ positive and I− negative ion groups in EOAI, which are anchored on the surface of SnO2 through –OH groups, can passivate the interface defects of perovskite films. Besides, the modified ETL has a smaller work function (WF) and EVB than pristine ones, which contributes to efficient charge transport and collection. Furthermore, the introduction of EOAI can also improve the crystallinity of the perovskite layer. As a result, PSCs with EOAI-modified SnO2 produce a champion power conversion efficiency (PCE) of 22.61%, and an improved environmental stability. At the same time, the 1.68 eV wide-band gap perovskite solar cell achieved a PCE close to 20% and the semitransparent device also achieved an efficiency of over 17%. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) with state-of-the-art efficiencies contain thermally unstable methylammonium (MA). Avoiding MA molecules usually leads to a severe decrease in the cell efficiency. In this work, a novel ion liquid (simplified as NDAPBF4) possessing a pyridine cation and BF4− anion were introduced to improve the performance of MA-free PSCs. The ion liquid NDAPBF4 can optimize the grain growth of the perovskite, leading to reduced carrier traps. In particular, NDAPBF4 served as an n-type dopant and boosted the electron transportation in the perovskite films, which further suppressed the carrier non-radiative recombination at the interface between the perovskite and the electron transporting layer. Finally, PSCs with a Cs0.05FA0.95PbI3 perovskite film as the absorber achieved a remarkable efficiency of 21.25%, which was one of the highest MA-free inverted perovskite solar cells up to date. PSCs doped with NDAPBF4 also gave excellent stability, which preserved 95% and 94% of the initial efficiency after being aged for 1000 h and 500 h under room temperature and elevated temperature at 85 °C, respectively. [ABSTRACT FROM AUTHOR]

Recently, prominent works using organic monomolecular layers (MLs) as efficient hole transport layers (ML-HTLs) in inverted perovskite solar cells (PSCs) have been reported to evidently promote device performance; however, these results were achieved individually on specific organic molecules and the power conversion efficiency (PCE) was less than 20%. Herein, to explore the feasibility of extending the strategy of organic ML-HTLs to efficient PSCs and the underlying general enhancement mechanism as well as further optimizing devices to achieve competitive performances, we report an universal ML-HTL strategy, employing MLs of widely used organic hole transport materials to construct HTLs, including small molecules and polymers that are hydrophobic/hydrophilic in nature. This strategy enabled optimal MLs to be formed on ITO substrates with full coverage; meanwhile, the optimal ML thickness resulted in maximum reduction of the charge carrier transit time. Generally, the ML-HTLs not only improve the wettability of the perovskite precursor that favors the formation of compact perovskite films, but also raise the effective work function of ITO towards better energy level alignment by the formation of interface dipoles. Consequently, a substantially improved fill factor of 81.86% and a champion PCE of 20.58% were achieved with the hydrophobic small molecule ML-HTL, which are record values ever reported for inverted PSCs based on ML-HTLs. Apart from small molecules, the use of ML-HTL based on either hydrophobic or hydrophilic polymers also showed improved performances. Furthermore, the better shrouded and more compact perovskite films on ML-HTLs increased the reproducibility of PSCs, which is beneficial for commercial applications. This work demonstrates the totality and in-depth understanding of the ML-HTL strategy and its potential for the development of highly efficient inverted PSCs. [ABSTRACT FROM AUTHOR]

We report on a method of precursor engineering to prepare high quality and stable perovskites based on formamidinium/methylammonium (FAMA) mixed-cations. CsI is commonly used to inhibit the photoinactive phase in FAMA perovskites. However, the hydrophilic nature of CsI would result in a structural instability issue at high relative humidity (RH). Besides, in inverted perovskite solar cells (PSCs) based on organic hole transport layers, the low conduction band minimum (CBM) of FAMA perovskites would lead to small open circuit voltage (Voc) (∼1.0 V), and thus additional surface passivation/modification layers are normally employed, indicating that it is essential to improve the basic precursors for high quality perovskite films. Herein, the proposed method is realized via ternary precursor alloying which endows the perovskite with increased grain size, enhanced crystallinity, reduced trap states, and a pure photoactive phase without the assistance of CsI. Without passivation/modification layers, the device Voc is enhanced markedly from 1.0 V to 1.1 V on average, and a champion power conversion efficiency of 20.7% with negligible hysteresis is achieved. Moreover, as they are free of hydrophilic CsI, both the photoactive perovskite films and devices exhibit excellent stability in ambient air. At high RH (70%), the optimized device without encapsulation only loses 16% of its efficiency after 1000 h storage, indicating the potential for the development of efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

Quasi-two-dimensional (Q-2D) perovskites ((RNH3)2MAn−1PbnI3n+1, RNH3 represents the organic spacer (mostly phenethylammonium (PEA) and n-butylammonium (BA)) and MA = methylammonium) have shown great potential for application in solar cells due to their intrinsic stability, where the organic spacer dominantly determines the Q-2D perovskite ambient stability and device performance. Current studies merely concentrate on unary organic spacer Q-2D perovskites, either using BA or PEA. Herein, for the first time, we have successfully designed and fabricated (PEA1−xBAx)2MA3Pb4I13 binary spacer-based Q-2D perovskite films, and demonstrated that the device using binary organic spacer-based Q-2D perovskite films has substantially better performance than that using either of the unary organic spacer-based Q-2D perovskite films. The (PEA0.8BA0.2)2MA3Pb4I13 binary spacer device yields a maximum power conversion efficiency of 15.7%, which outperforms the efficiency record (12–14%) for unary spacer (PEA or BA) Q-2D perovskite devices. In particular, a peak open-circuit voltage of 1.21 V is achieved due to a non-radiative recombination loss of ∼100 mV, the lowest reported loss value for Q-2D perovskite devices. The high device performance results from binary-spacer-induced intensified film surface quality, preferable vertical orientation of crystals and improved film optoelectronic properties as well as obviously decreased device recombination losses. These findings open up a new avenue for the rational design of Q-2D perovskite materials with polynary organic spacer. [ABSTRACT FROM AUTHOR]

Interface modifying layers (IMLs) play a pivotal role in the improved performance of perovskite solar cells (PSCs). Herein, we report a new IML based on Bphen:Cs2CO3:BCP (BCB), which is inserted at the interface of phenyl-C61-butyric acid methyl ester (PC61BM) and a Ag electrode. Consequently, the efficiency of PSCs is significantly improved by 5% (from 17.57% to 18.29%), mainly due to the increased open circuit voltage (VOC). It is revealed by ultraviolet photoelectron spectroscopy (UPS) that the work function of Ag is reduced from 4.68 eV to 3.90 eV, after being modified by BCB due to the formation of a strong negative interfacial dipole at the Ag/BCB interface. The decreased work function of Ag improves the ohmic contact between PC61BM and Ag, facilitating carrier extraction and suppressing the charge recombination at the interface of PC61BM and the Ag electrode. As a result, the reverse saturation current of the final PSC is decreased by approximately one order of magnitude, which is consistent with a larger VOC. Our work provides a comprehensive understanding of the interface between a metal electrode and an electron transporting layer (ETL), and hence paves a way towards better interfacial engineering and highly efficient solar cells. [ABSTRACT FROM AUTHOR]

A delicate control of crystallization and morphology of perovskite absorbers is critical to obtain high performance hybrid perovskite solar cells (PSCs). Here, we have developed a novel crystallization strategy which involves hydration water induced intermediate phase formation under heat assisted spin-coating processing (HASP) to manipulate the morphology and grain size of perovskite films, and thus it can avoid the use of toxic and volatile antisolvents used in conventional one-step solution processes to make PSCs. During HASP, impressive morphological evolution of films occurs with the formation of CH3NH3PbI3·xH2O perovskite intermediate phases. With ingenious control of the crystallization kinetics, highly crystalline perovskite films with fewer defect states and high carrier lifetimes are obtained. The corresponding PSCs exhibit a power conversion efficiency (PCE) of 19.12% with a stabilized power output efficiency of 18.89% at the maximum power point, which is a 70% enhancement compared to that of conventional one-step process based PSCs. Furthermore, the PSC fabricated by the HASP method achieved a PCE of 15.47% with an active area of 1.2 cm2. Moreover, the flexible PSCs fabricated by the HASP method achieved a record efficiency of 14.87% with negligible hysteresis for PEDOT:PSS-based flexible inverted PSCs. Our work opens up a new avenue for morphology and crystallization control through hydration water induced intermediate phase formation under HASP, which paves the way toward further enhancing the device performance of perovskite solar cells. [ABSTRACT FROM AUTHOR]

Hierarchical materials are a favourite for energy storage/harvesting technologies, such as supercapacitors and electrically-driven hydrogen production. In this work, we report a robust and highly active nanomaterial for pseudocapacitors and hydrogen production by growing vanadium pentoxide on the surface of nickel sulfide (denoted as V2O5@Ni3S2). V2O5@Ni3S2 shows a capacitance of up to 854 F g−1 at a current density of 1 A g−1 and good rate capability. The capacitance can retain ca. 60% of the initial specific capacitance even after 1000 cycles at a current density of 1 A g−1. For the hydrogen evolution reaction (HER), the overpotential of V2O5@Ni3S2 is around 95 mV at 10 mA cm−2. The excellent electrochemical performance of the V2O5@Ni3S2 hybrid is attributed to the synergistic effect between vanadium pentoxide and nickel sulfide for pseudocapacitors, and the V2O5@Ni3S2 interface and V–S active bonding in the hierarchical structure for the HER. This work demonstrates an effective structure design for supercapacitors with high energy density and for efficient hydrogen production with high catalytic activity by incorporating metal oxide with metal sulfide. [ABSTRACT FROM AUTHOR]

An unconventional reductive quenching cycle was developed to realize the visible-light-induced thiotrifluoromethylation of terminal alkenes. CF3SO2Na was used as an easy to handle CF3 radical source to afford the desired products in moderate to good yields. Mild reaction conditions and a broad substrate scope feature in this transformation. [ABSTRACT FROM AUTHOR]

Methylammonium lead-iodide (CH3NH3PbI3, hereafter referred to as MAPbI3) perovskite has emerged as a dazzling nova in the solar cell realm. To date, the surface physics of these materials is still puzzling, but in this work, we demonstrate that the optical dynamics in MAPbI3 is primarily determined by the surface states. Pb dangling bonds on the surface of MAPbI3 introduce shallow electronic states. The carrier localization effect for these electronic states is rather weak as the lifetimes of the carriers on the iodine-poor surface are comparative to those in the interior region of MAPbI3. In contrast, rich-iodine on the surface of MAPbI3 induces deep trap centers for the carriers, which are detrimental to long carrier diffusion lengths. It is further proved that the surface passivation, which surprisingly prolongs the carrier diffusion lengths, mainly works on the rich-iodine on the surface rather than the Pb dangling bonds. This better understanding of the surface physics could provide essential information for improving the performance of photoelectronic devices based on MAPbI3 perovskites. [ABSTRACT FROM AUTHOR]

Solution-processed hybrid perovskite of CH3NH3PbI3 (MAPbI3) exhibits an abnormal luminescence behavior at around the tetragonal–orthorhombic phase transition temperature. The combination of time resolved photoluminescence (PL), variable excitation power PL, and variable-temperature X-ray diffraction (XRD) allows us to clearly interpret the abnormal luminescence features in the phase transition region of MAPbI3. Both PL and XRD results unambiguously prove the coexistence of the tetragonal and orthorhombic phases of MAPbI3 in the temperature range of 150 to 130 K. The two luminescence features observed in the orthorhombic phase at T ＜ 130 K originate from free excitons and donor–acceptor-pair (DAP) transitions, respectively. The comprehensive understanding of optical properties upon phase transition in MAPbI3 will benefit the development of new optoelectronic devices. [ABSTRACT FROM AUTHOR]

Solution-processed hybrid perovskite of CH3NH3PbI3 (MAPbI3) exhibits an abnormal luminescence behavior at around the tetragonal-orthorhombic phase transition temperature. The combination of time resolved photoluminescence (PL), variable excitation power PL, and variable-temperature X-ray diffraction (XRD) allows us to clearly interpret the abnormal luminescence features in the phase transition region of MAPbI3. Both PL and XRD results unambiguously prove the coexistence of the tetragonal and orthorhombic phases of MAPbI3 in the temperature range of 150 to 130 K. The two luminescence features observed in the orthorhombic phase at T < 130 K originate from free excitons and donor-acceptor-pair (DAP) transitions, respectively. The comprehensive understanding of optical properties upon phase transition in MAPbI3 will benefit the development of new optoelectronic devices.