Search

Nickel oxide (NiOX) is a desirable hole‐transporting material for perovskite solar cells owing to their merits of low‐cost, stable, and readily scalable. However, the NiOX|perovskite interface suffers from serious recombination and poor photostability because of the interfacial redox reactions. Herein, NiOX nanoparticles with tunable size have been synthesized at low temperatures by controlling the reactivity of the hydrolysis reaction. A self‐assembled monolayer composed of a ruthenium complex, i.e., C106, is then introduced to optimize the interfacial properties. The C106 molecule chemically bonds to NiOX via carboxyl acid group, which passivates the surface defects of NiOX and suppresses the negative redox reaction at the interface. The modification leads to an improvement in perovskite film morphology, crystallization, and band alignment. As a result, the efficiency of solar cells has been improved from 18.1% to 20.5%. More importantly, the modified solar cells retain >80% of their initial performance after continuous operation under 100 mW cm−2 irradiation for 800 h, which is much enhanced than the unmodified devices. [ABSTRACT FROM AUTHOR]

Rapid processing technologies of perovskite solar cells (PSCs) offer an exciting approach to raise the rate of production. Herein, a rapid microwave‐annealing process (MAP) is reported to replace the traditional hotplate annealing process (HAP) and the processing period of perovskite is reduced to less than 1 min. Benefiting from the penetrability and simultaneity of microwave irradiation, the MAP method can effectively eliminate miscellaneous phases and thus achieve >1 µm large‐size crystal grains in perovskite films. These MAP treated perovskite films exhibit pure crystalline phase, long charge‐carrier lifetime, and low defect density, which can substantially improve the PSC efficiency without requiring an additional enhancer/passivation layer. The inverted planar PSCs present enhanced power conversion efficiency from 18.33% (HAP) to 21.59% (MAP) and good stability of >1000 h lifetime without encapsulation under ambient conditions. In addition, MAP can be applied to a large‐size (10 cm × 10 cm) perovskite film fabrication as well as a broader tolerance in environmental temperature and precursor concentration, making it a reliable method for repeatably practical fabrication of perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

Abstract The remarkable power conversion efficiency of perovskite solar cells (PSCs) is overshadowed by concerns about their stability, and its degradation mechanism remains elusive. PSCs are reported to suffer long-term degradation under real working conditions. In this work, we systematically studied the degradation mechanism of PSCs with various device configurations (planar, meso and inverted device structure) by continuous 12-h day/night cycling tests. The fatigue phenomenon, defined in our previous work, was observed both in planar and meso devices. A relationship between the fatigue instability and device-physics of PSCs is established. Through a comparative analysis of results from day/night cycling tests, bulk/interfacial morphology analysis, and transient photocurrent/photovoltage decay measurements, we identify the fatigue behavior in the day/night cycling tests by a cyclic ion movement mechanism, where ions migrate towards the electrode interfaces under illumination and move back to the bulk in the dark. This cyclic migration of ions generates defects in bulk perovskite without destroying the crystal structure. The present study offers a new approach to evaluate the stability of PSCs, contributing to better understanding of degradation mechanisms that are critically important for applications of this novel photovoltaic technology. Graphical abstract fx1 Highlights • Fatigue stability of different configuration PSCs were studied, and inverted PSCs showed negligible fatigue. • Charge extraction, recombination and accumulation at the interfaces have serious impact on fatigue stability. • The relationship between the fatigue and device-physics of PSCs has been established. • The relationship between fatigue and ionic defects has been identified. [ABSTRACT FROM AUTHOR]

The microstructure of solution-processed organometallic lead halide perovskite thin films prepared by the 'gas-assisted' method is investigated with synchrotron-based techniques. Using a combination of GIWAXS and NEXAFS spectroscopy the orientational alignment of CH3NH3PbI3 crystallites and CH3NH3+ cations are separately probed. The GIWAXS results reveal a lack of preferential orientation of CH3NH3PbI3 crystallites in 200-250 nm thick films prepared on both planar TiO2 and mesoporous TiO2. Relatively high efficiencies are observed for device based on such films, with 14.3% achieved for planar devices and 12% for mesoporous devices suggesting that highly oriented crystallites are not crucial for good cell performance. Oriented crystallites however are observed in thinner films (≈60 nm) deposited on planar TiO2 (but not on mesoporous TiO2) indicating that the formation of oriented crystallites is sensitive to the kinetics of solvent evaporation and the underlying TiO2 morphology. NEXAFS measurements on all samples found that CH3NH3+ cations exhibit a random molecular orientation with respect to the substrate. The lack of any NEXAFS dichroism for the thin CH3NH3PbI3 layer deposited on planar TiO2 in particular indicates the absence of any preferential orientation of CH3NH3+ cations within the CH3NH3PbI3 unit cell for as-prepared layers, that is, without any electrical poling. [ABSTRACT FROM AUTHOR]

Thin-film photovoltaics based on alkylammonium lead iodide perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology. To date, the perovskite layer in these efficient solar cells has generally been fabricated by either vapor deposition or a two-step sequential deposition process. We report that flat, uniform thin films of this material can be deposited by a one-step, solvent-induced, fast crystallization method involving spin-coating of a DMF solution of CH3NH3PbI3 followed immediately by exposure to chlorobenzene to induce crystallization. Analysis of the devices and films revealed that the perovskite films consist of large crystalline grains with sizes up to microns. Planar heterojunction solar cells constructed with these solution-processed thin films yielded an average power conversion efficiency of 13.9±0.7 % and a steady state efficiency of 13 % under standard AM 1.5 conditions. [ABSTRACT FROM AUTHOR]

Although high efficiencies have been achieved for perovskite solar cells (PSCs), stability issues are still the key barriers for commercial applications. Herein, we carry out a systematic doping of non-radiative alkaline metal ions (Cs, Rb, K, Na, Li) to perovskite, studying their effects on perovskite morphology, electrical stability and performance of PSCs. The hysteresis related stability issues are also investigated at different conditions, such as steady-state power output, aging, repeated voltage sweeping, varied pre-scan voltage bias, etc. It is found the hysteresis becomes much severer at different test conditions for the devices doped with small sized Li and Na. While the subsized Rb and K ions (compared to Cs) doping can significantly enhance the crystallinity of perovskite and reduce the hysteresis that is also more stable. The crystallization, morphologies, time-resolved photoluminescence, electrochemical impedance spectroscopy were conducted to investigate the properties of the doped perovskite films to understand the relationship between the film quality and device performance. With a proper combination of Cs, Rb, K ions doping in PSCs, a high PCE over 20% is achieved with an enhanced electrical stability. Moreover, an over 17% efficiency 7 × 7 cm2 perovskite solar cell module is realized by this strategy, with a certified PCE of 16.5% (aperture area of 20.78 cm2) without hysteresis. [ABSTRACT FROM AUTHOR]