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Methylammonium chloride (MACl) additive is almost irreplaceable in high‐performance formamidine perovskite photovoltaics. Nevertheless, Some of the problems that can arise from adding MACl are rarely mentioned. Herein, it is proposed for the first time that the addition of MACl would cause the non‐stoichiometric ratio in the perovskite film, resulting in the halogen vacancy. It is demonstrated that the non‐synchronous volatilization of methylamine cations and chloride ions leads to the formation of halogen vacancy defects. To solve this problem, the NH4HCOO is introduced into the perovskite precursor solution to passivate the halogen vacancy. The HCOO− ions have a strong force with lead ions and can fill the halogen vacancy defects. Consequently, the champion devices' power conversion efficiency (PCE) can be improved from 21.23% to 23.72% with negligible hysteresis. And the unencapsulated device can still retain >90% of the initial PCE even operating in N2 atmosphere for over 1200 h. This work illustrates another halogen defect source in the MACl‐assisted formamidine perovskite photovoltaics and provides a new route to obtain high‐performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

The perovskite photovoltaic field has developed rapidly within a decade. In particular, formamidinium (FA)‐rich perovskite allows a broad absorption spectrum, and is considered to be one of the most promising perovskite materials. Great progress has been achieved, and most recorded high‐efficient perovskite solar cells (PSCs) used the FA‐rich perovskite light absorption layer. However, the black α‐phase formamidinium lead iodide (FAPbI3) perovskite easily transforms into an undesirable δ‐phase at a low temperature. Thus, researchers have put a lot of effort into deeply understanding the phase transformation and stabilization mechanism of FA‐rich perovskite. Herein, the fundamental physical properties of FAPbI3 materials, including crystal structure, phase‐transition temperature, charge‐carrier dynamics, etc. are summarized, and establish a complete phase evolution with temperature by reviewing previous reports. The intrinsic and external factors are subsequently discussed for influencing the stability of FAPbI3 perovskite and the remarkable breakthroughs of FA‐rich PSCs in recent years are reviewed. Moreover, a series of strategies to stabilize FA‐rich perovskite is summarized, including but not limited to compositional engineering, passivating engineering, processing engineering, and strain engineering. Finally, several new viewpoints are provided for improving the efficiency and stability of PSCs. This review may be regarded as a reference project for preparing high‐efficient and stable perovskite photovoltaic devices. [ABSTRACT FROM AUTHOR]

• Double modification – simultaneously using MoS 2 as buffer layer and additives. • MoS 2 film acts as a protective and ideal electron blocking candidate. • MoS 2 doped CH 3 NH 3 PbI 3 , enhance the quality of the perovskite film. • CH 3 NH 3 PbI 3 : MoS 2 heterojunction promote charge transfer. Organic-inorganic perovskite solar cells emerge as one of the most promising photovoltaic technology due to its high performances. Particularly, inverted perovskite device architecture, due to low temperature processing, have a great potential in commercialization. High-crystalline quality perovskite film and interfacial passivation are essential to yield high performance devices. In this work, we employ a simple strategy of using molybdenum disulfide (MoS 2) as both the interfacial layer and the additive to prepare efficient PSCs. MoS 2 as an additive in perovskite can form the CH 3 NH 3 PbI 3 :MoS 2 heterostructure, resulting in the homogeneous perovskite film with larger crystal grains. In addition, MoS 2 as the buffer layer (BL) between poly (3,4-ethylene dioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) and perovskite can prevent the decomposition of perovskite film by avoiding the direct contact with the hydrophilic PEDOT:PSS films. On tedious optimization, the champion device based on active layer of CH 3 NH 3 PbI 3 :MoS 2 (10 v%) as well as employing MoS 2 buffer layer shows a remarkable improvement in the power conversion efficiency (PCE) (from 15.29% to 18.31%) and a better stability, with 87% of the initial efficiency sustained after 20 days. Our finding herein provides a promising way to fabricate high efficiency and stable photovoltaic devices. [ABSTRACT FROM AUTHOR]

Carbon-based perovskite solar cells aroused huge attention for their simple, low-cost device fabrication processing and excellent stability. However, the fully low-temperature preparation and flexibility of carbon-based perovskite solar cells remain huge challenges. Here we demonstrate the fabrication of carbon-based perovskite solar cells processed at fully low-temperature, which take thermally evaporated cadmium sulfide as efficient electron transport layer, and obtain an optimal power conversion efficiency of 13.22%. With the decoration of PCBM, the separation of charges at the interface is facilitated and the recombination is hindered, so a higher fill factor is obtained and the efficiency is further improved to 14.28%. Our devices also exhibit good long-term durability and excellent ultraviolet stability. Based on the fully low-temperature preparation process, carbon-based flexible devices are further developed with an optimal efficiency over 9% and considerable mechanical stability, which can serve as the roof-top photovoltaics and power sources for wearable devices. Image 1 • Fully low-temperature processed and flexible carbon-based PSCs with excellent efficiency and stability are demonstrated. • First use of CdS as electron transport layer for carbon-based PSCs. • With the decoration of PCBM, efficiency of the best-performing device is greatly enhanced. [ABSTRACT FROM AUTHOR]

Abstract Fullerenes have been widely used as the electron transport layers (ETL) for planar-heterojunction perovskite solar cells (PSCs), due to their superior abilities in electron transporting, hysteresis suppression and low-temperature processing. Here, we demonstrate a novel inverted PSC with evaporated C 60 as ETL and dopant-free copper phthalocyanine (CuPc) as hole transport layer (HTL). The C 60 ETL can not only transport photogenerated electrons, but also passivate grain boundaries and surfaces of perovskite films effectively. By optimizing the thickness of the C 60 ETL, a champion power conversion efficiency (PCE) of 16.72% is obtained with almost no hysteresis and less than 10% decay in efficiency is observed during a two-week stability test. To the best of our knowledge, this is the highest efficiency of the inverted PSCs employing CuPc as HTL. For comparison, the devices using PCBM as ETL are also prepared and only achieve a highest efficiency of 15.74%. Various characterizations and analyses attest the enhanced charge transport and extraction as well as suppressed charge recombination and hysteresis for the C 60 -based devices. Since all the processes are accomplished under a low temperature, this enable us to fabricate flexible PSCs on polyethylene terephthalate (PET) substrates with a highest PCE of 12.96%. Our work provides a new strategy for fabricating cost-effective, highly efficient and hysteresis-free flexible PSCs in mass production. Graphical abstract Novel efficient C 60 -based inverted perovskite solar cells with negligible hysteresis are demonstrated. A champion power conversion efficiency (PCE) of 16.72% and 12.96% is obtained for the devices prepared on rigid and flexible substrates, respectively. Image 1 Highlights • Novel inverted perovskite solar cells (PSCs) with Cu-phthalocyanine and C 60 as HTL and ETL, respectively. • 16.72% efficiency is obtained, which is the highest efficiency of the inverted PSCs employing CuPc as HTL. • 12.96% efficiency is obtained for the flexible device. • Almost no hysteresis is observed. • Cost-effective, easy to prepare and highly stable. [ABSTRACT FROM AUTHOR]

Abstract Zinc oxide (ZnO) as an electron transport material has been used in regular planar perovskite solar cells (PSCs). Herein, ZnO nanoparticles serve as an additive directly in perovskite active layer in order to fabricate a bulk-heterojunction inverted planar PSC. The CH 3 NH 3 PbI 3-x Cl x :ZnO bulk heterojunction is prepared by mixing ZnO nanoparticles into CH 3 NH 3 PbI 3-x Cl x precursor solution. ZnO nanoparticles act as catalytic centers and induce the growth of perovskite grains leading to the formation of large-size perovskite crystals. Remarkably, hysterysis-free power conversion efficiency of 17.26% is achieved when precisely control the concentration of ZnO nanoparticles in CH 3 NH 3 PbI x Cl 3-x :ZnO bulk heterojunction active layer. The presence of ZnO nanoparticles in the perovskite films enhances the conductivity and electron mobility. Efficient charge injection of CH 3 NH 3 PbI x Cl 3-x :ZnO film can improve charge extraction in the PSCs. Moreover, the PSCs with CH 3 NH 3 PbI x Cl 3-x :ZnO bulk heterojunction exhibit high fill factor of 77.3% and short current density of 22.71 mA cm−2, which is attributed to improved perovskite quality. The bulk heterojunction structure is fabricated by combining perovskite and metal oxides, which is of great importance to the development and commercialization of PSCs in the future. Graphical abstract Image 1 Highlights • A CH 3 NH 3 PbI 3-x Cl x :ZnO bulk heterojunction exits in the perovskite solar cell. • ZnO nanoparticles improve light harvesting efficiency of perovskite solar cell. • ZnO nanoparticles lead to the formation of large-size perovskite crystals. • ZnO nanoparticles improve conductivity and electron mobility of perovskite film. [ABSTRACT FROM AUTHOR]

Electron transport layer (ETL), functioning as the electron transportation and extraction layer as well as hole-blocking layer, plays an important role in planar perovskite solar cells (PSCs). Majority of the state-of-the-art PSCs contain a TiO 2 ETL always requiring a high temperature (500 °C) treatment, which is both energy-consuming and incompatible with flexible substrates, thus hindering large-scale application in flexible devices. Here, we demonstrated a low-temperature (70 °C) solution-processed Mg-doped rutile TiO 2 as ETL in planar PSCs, while the thermal-evaporated copper phthalocyanine (CuPc) and doctor-bladed carbon were introduced as the hole transport layer (HTL) and counter electrode, respectively. The as-prepared PSC obtains a 15.73% power conversion efficiency (PCE), which is quite an excellent efficiency among carbon-based planar PSCs, getting an increase by 16% compared to the 13.56% PCE of the pristine TiO 2 -based device. The prominent increment is mainly attributed to the faster charge extraction, better electrical conductivity and suppressed charge recombination of Mg-doped TiO 2 . Besides, using highly stable CuPc and commercial carbon makes the as-prepared PSCs highly durable over 30 days when exposed to the ambient air with a relative humidity of 50%. Since all the processes are conducted under 100 °C, our work paves a way for developing cost-effective and highly stable PSCs compatible with flexible substrates. [ABSTRACT FROM AUTHOR]

In this work, an efficient and stable inverted planar perovskite solar cell (PSC) with water additive has been prepared in ambient air. Adding moderate water additive to CH 3 NH 3 PbI 3−x Cl x precursor solution leads to growth in quality of CH 3 NH 3 PbI 3−x Cl x film, because the boiling point of water is lower than that of N, N-dimethylformamide. The annealing temperature of the CH 3 NH 3 PbI 3−x Cl x film is controlled to 105 °C (slightly higher than the boiling point of water) to obtain the dense perovskite film rapidly in ambient environment with ~ 40% relative humidity. The highest power conversion efficiency (PCE) of PSC with water additive is 14.02%, higher than that (11.17%) of the reference device without water additive. In addition, the aqueous CH 3 NH 3 PbI 3−x Cl x solution is transformed into the stable perovskite film through the method of rapid annealing. The stable CH 3 NH 3 PbI 3−x Cl x ·nH 2 O system can resist the decomposition of perovskite film and weaken iodide ion migration in PSCs, which enhance stability of the device under the atmospheric environment. After being stored in the air for 120 h, the PSC device with water additive still has an PCE of 12.01%, higher than that (1.64%) of the reference device. [ABSTRACT FROM AUTHOR]

We demonstrate the application of low-temperature carbon counter electrode in fabricating large-area hole-conductor-free perovskite solar cell. A mesoscopic TiO 2 film was deposited on a transparent conductive fluorine-doped tin oxide substrate by screen printing method. Then commercial conductive carbon slurry was printed to prepare the counter electrode at a temperature of 130 °C. The light absorber, CH 3 NH 3 PbI 3 , was formed instantly inside the pores of the entire TiO 2 /carbon layer upon single-step deposition of CH 3 NH 3 PbI 3 precursor. The devices were characterized with XRD, SEM, and UV–vis absorption spectroscopy. As a result, an energy conversion efficiency of 3.3% with an active area of 2.25 cm 2 was got under AM1.5G condition and there was no obvious decay during a testing period of 624 h. The carbon counter electrode has the features of low-cost and low-temperature preparation, giving it potential for application in the large-scale flexible fabrication of perovskite solar cells in the future [ABSTRACT FROM AUTHOR]

Flexible perovskite solar cells (PSCs) such as inverted PSCs are gaining increasing attention due to their wide range of potential applications, while the selection of stable, high conductivity and energy level suitable hole transport layers (HTLs) is still challenging. Here we introduce dopant-free copper phthalocyanine (CuPc) as HTL in inverted planar PSCs, and demonstrate improved photovoltaic performance and increased stability with high reproducibility and uniformity compared to the PEDOT:PSS based devices. The champion efficiency of PSCs is achieved by 15.4% on rigid substrates and 12.8% on flexible substrates, respectively. The flexible devices also exhibit excellent bending stability, retaining ∼85% of the original power conversion efficiency (PCE) after 3000 bending cycles at r = 5 mm without encapsulation. Our study provides a new strategy for fabricating cost-effective, scalable and flexible PSCs with high efficiency, little hysteresis, and excellent stability. [ABSTRACT FROM AUTHOR]

SnO 2 electron transport layers (ETLs) had an essential role in the n-i-p structure of perovskite solar cells. Improving the quality of the electron transport layer and enhancing interfacial contacts were key factors in the fabrication of high-performance perovskite solar cells. Therefore, a non-ionic polymeric polyacrylamide (PAM) modified SnO 2 colloidal solution with improved clustering of SnO 2 nanoparticles was presented to form a uniform and dense SnO 2 electron transport layer. The results demonstrated that no pinhole pores were found at the interface where the PAM-modified electron transport layer and the light absorbing layer came into contact, a structure that facilitated carrier transport and reduced carrier recombination at the interface location. Further beneficial effects were revealed by femtosecond Fs-TA measurements and trap of states (tDOS) analysis, where the carrier lifetime τ 2 decreased from 306.7 ps to 137.8 ps and the trap density of states of the film also decreased significantly. Correspondingly, the SnO 2 -PAM device exhibited an optimum efficiency of 21.61 %. Fantastic device stability was obtained due to the interaction of excellent contact at the SnO 2 /FAPbI 3 interface, and 85 % of the initial efficiency was maintained when placed in air for 1000 h for photo-aging tests, thereby improving the stability of FAPbI 3 grains. This method of improving the quality of tin oxide colloidal solutions provided a novel and simple way to prepare efficient perovskite solar cells. [ABSTRACT FROM AUTHOR]

α-Formamidinium lead iodide (α-FAPbI 3) has become one of the most promising candidate materials for stable perovskite solar cells (PSCs) owing to their outstanding optoelectronic properties and high thermal stability. The crystallinity of the active layer of perovskite is essential to the performance of perovskite solar cells. In this paper, we added lead acetate Pb(Ac) 2 as a grain growth agent into the perovskite precursor solution to prepare high-efficiency and stable perovskite solar cells. It was revealed that the crystals of Pb(Ac) 2 -modified film grew selectively along the [200] direction and that the FAPbI 3 active layer grains were arranged neatly and densely, due to the significant influence of a moderate amount of weakly acidic Ac- on the crystal growth of FAPbI 3. The relative reduction in its grain boundaries led to the decrease in the grain boundary impedance, and it was easier for electrons to perform long-range migration in the perovskite active layer. The beneficial effects of Pb(Ac) 2 were further expiored by femtosecond Fs-TA measurements and density of states (tDOS) analysis, where the carrier lifetimes τ 2 was increased from 482.4 ps to 1340 ps, and the trap density of film states was significantly reduced. The filling factor (FF) and power conversion efficiency (PCE) were increased from 76.5% and 19.7–81.1% and 21.8%, respectively, the Pb(Ac) 2 devices were placed in air for 800 h for the light aging test, and the test results still maintained 90% of the original efficiency, which improved the stability of FAPbI 3 crystals. • Pb(Ac) 2 as an additive to modulate the crystalline quality of perovskite active layer films. • Perovskite solar cell defect reduction and carrier lifetime increase by Pb(Ac) 2 modification. • The Pb(Ac) 2 -modified active layer grains have preferential orientation and orderly arrangement. • 81.1% filling factor and 21.8% efficiency are achieved for a single PSC cell with excellent stability. [ABSTRACT FROM AUTHOR]

The development of perovskite solar cells has improved rapidly. However, PSCs generally suffer from instability, due to the detrimental defects. Additive engineering is a favorable method for defect passivation. In this work, the linear pseudo-halogen salt, KSCN, is introduced into the MAPbI 3 perovskite film to improve the performance of PSC. The trap density of cells with SCN− is decreased significantly. The SCN− not only can fill halogen vacancies to reduce the halide-related defects, but also can interact with the uncoordinated Pb2+ via coordinate bond to stabilize perovskite lattice structure. Moreover, the performance of devices with other linear pseudo-halogen anions (OCN−, SeCN−) are also investigated. Due to the improved short circuit current density, the power conversion efficiency of devices increases from 18.02% (PVK) to 20.41% (PVK–SCN-), 19.53% (PVK–OCN-) and 19.23% (PVK–SeCN-), respectively. After introducing pseudo-halide anions, the devices showed robust stability under the ambient environment. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid perovskite materials with distinctive optoelectronic properties have attracted much interest in the field of solar cells. As the light absorber, the quality of perovskite films is crucial to the performances of perovskite solar cells. Anti-solvent engineering seems to be an efficient method in preparing high-quality perovskite films, but mostly used anti-solvents are toxic, such as chlorobenzene (CB)， which is harmful to the environmental protection. In the present work, we used the green anti-solvent diethyl carbonate (DEC) instead of CB, demonstrated that the DEC engineered CH 3 NH 3 PbI 3 film exhibits improved morphology and crystallinity as well as reducing defects, which can be attributed to the interaction between DEC and the solvent dimethyl sulfoxide (DMSO). The DEC anti-solvent assisting yields efficient CH 3 NH 3 PbI 3 perovskite solar cells with a champion power conversion efficiency of 20.20% and a steady state efficiency of 86% over a period of 20 days of storage under ambient conditions. The present study provides a viable path way to design green and effective perovskite solar cells in the future. [Display omitted] • Developed a green solvent-assisted perovskite crystallization method. • Formed uniform and compact perovskite films with large grains. • High-quality perovskite films prepared by green anti-solvent diethyl carbonate. [ABSTRACT FROM AUTHOR]

The possible exhaustion of fossil fuels in the near future and soaring global energy demand have driven the search for new types of sustainable and renewable alternatives. Perovskite (CHNHPbX, X = I, Br, Cl) solar cells are a type of solar cell based on a perovskite absorber, most commonly a tin halide-based or hybrid organic-inorganic lead material, as the visible-light sensitizer layer, which produces electricity from sunlight. Recently, perovskite solar cells have received substantial worldwide attention. Compared with traditional solar cells, the perovskite solar cells can obtain high efficiency with a simple architecture and via a cost-effective process. In the latest 5 years, the efficiency of perovskite solar cells to convert power has skyrocketed from 3.8 % to more than 19.3 %. It is the fastest advancing solar technology to date. The highest efficiency demonstrated by perovskite solar cells is higher than that of dye-sensitized solar cells (DSSCs). A lager number of research groups have demonstrated that perovskite solar cells may ultimately boost efficiency as high as 25 %. The high efficiency and cheap production costs make it evident that perovskite solar cells have great potential to be commercialized soon. In this review, the history, materials, processing and architecture of solar cells are discussed to obtain a better understanding of high-performance perovskite solar cells. [ABSTRACT FROM AUTHOR]