Abstract
Rational design of heterostructures opens up new opportunities as an ideal catalyst system for lithium polysulfides conversion in lithium-sulfur battery. However, its traditional fabrication ...process is complex, which makes it difficult to reasonably control the content and distribution of each component. In this work, to rationally design the heterostructure, the atomic layer deposition is utilized to hybridize the TiO
2
-TiN heterostructure with the three-dimensional carbon nanotube sponge. Through optimizing the deposited thickness of TiO
2
and TiN layers and adopting the annealing post-treatment, the derived coaxial sponge with uniform TiN-TiO
2
heterostructure exhibits the best catalytic ability. The corresponding lithium-sulfur battery shows enhanced electrochemical performance with high specific capacity of 1289 mAh g
−1
at 1 C and capacity retention of 85% after 500 cycles at 2 C. Furthermore, benefiting from the highly porous structure and interconnected conductive pathways from the sponge, its areal capacity reaches up to 21.5 mAh cm
−2
.
Orthorhombic phases for perovskite solar cellsThe power conversion efficiencies (PCEs) of all-inorganic perovskites are lower than those of materials with organic cations. This is in part because ...these materials have larger bandgaps. The cubic crystal phases of these materials also exhibit poor stability. Wang et al. synthesized the orthorhombic β-phase of CsPbI3 from HPbI3 and CsI. The material exhibited higher stability and a more favorable bandgap, which allowed for PCEs of 15%. Passivation of the surface trap state with choline iodide boosted PCEs to 18%.Science, this issue p. 591Although β-CsPbI3 has a bandgap favorable for application in tandem solar cells, depositing and stabilizing β-CsPbI3 experimentally has remained a challenge. We obtained highly crystalline β-CsPbI3 films with an extended spectral response and enhanced phase stability. Synchrotron-based x-ray scattering revealed the presence of highly oriented β-CsPbI3 grains, and sensitive elemental analyses—including inductively coupled plasma mass spectrometry and time-of-flight secondary ion mass spectrometry—confirmed their all-inorganic composition. We further mitigated the effects of cracks and pinholes in the perovskite layer by surface treating with choline iodide, which increased the charge-carrier lifetime and improved the energy-level alignment between the β-CsPbI3 absorber layer and carrier-selective contacts. The perovskite solar cells made from the treated material have highly reproducible and stable efficiencies reaching 18.4% under 45 ± 5°C ambient conditions.
In several photovoltaic (PV) technologies, the presence of electronic defects within the semiconductor band gap limit the efficiency, reproducibility, as well as lifetime. Metal halide perovskites ...(MHPs) have drawn great attention because of their excellent photovoltaic properties that can be achieved even without a very strict film‐growth control processing. Much has been done theoretically in describing the different point defects in MHPs. Herein, we discuss the experimental challenges in thoroughly characterizing the defects in MHPs such as, experimental assignment of the type of defects, defects densities, and the energy positions within the band gap induced by these defects. The second topic of this Review is passivation strategies. Based on a literature survey, the different types of defects that are important to consider and need to be minimized are examined. A complete fundamental understanding of defect nature in MHPs is needed to further improve their optoelectronic functionalities.
Watching the defects: Defects play a pivotal role in the overall performance of perovskite solar cells. This Review focuses on central questions of “what defects exist in metal halide perovskites” and “how can one reduce detrimental defects towards high‐performance perovskite solar cells”.
The current challenges (e.g., stability, hysteresis, etc.) in organometal halide perovskite solar cell research are closely correlated with surfaces and interfaces. For instance, efficient generation ...of charges, extraction, and transport with minimum recombination through interlayer interfaces is crucial to attain high-efficiency solar cell devices. Furthermore, intralayer interfaces may be present in the form of grain boundaries within a film composed of the same material, for example, a polycrystalline perovskite layer. The adjacent grains may assume different crystal orientations and/or have different chemical compositions, which impacts charge excitation and dynamics and thereby the overall solar cell performance. In this Perspective, we present case studies to demonstrate (1) how surfaces and interfaces can impact material properties and device performance and (2) how these issues can be investigated by surface science techniques, such as scanning probe microscopy, photoelectron spectroscopy, and so forth. We end this Perspective by outlining the future research directions based on the reported results as well as the new trends in the field.
Organic–inorganic halide perovskite materials (e.g., MAPbI3, FAPbI3, etc.; where MA = CH3NH3 +, FA = CH(NH2)2 +) have been studied intensively for photovoltaic applications. Major concerns for the ...commercialization of perovskite photovoltaic technology to take off include lead toxicity, long-term stability, hysteresis, and optimal bandgap. Therefore, there is still need for further exploration of alternative candidates. Elemental composition engineering of MAPbI3 and FAPbI3 has been proposed to address the above concerns. Among the best six certified power conversion efficiencies reported by National Renewable Energy Laboratory on perovskite-based solar cells, five are based on mixed perovskites (e.g., MAPbI1–x Br x , FA0.85MA0.15PbI2.55Br0.45, Cs0.1FA0.75MA0.15PbI2.49Br0.51). In this paper, we review the recent progress on the synthesis and fundamental aspects of mixed cation and halide perovskites correlating with device performance, long-term stability, and hysteresis. In the outlook, we outline the future research directions based on the reported results as well as related topics that warrant further investigation.
Abstract
Perovskite solar cells (PSCs) have attracted much attention due to their low-cost fabrication and high power conversion efficiency (PCE). However, the long-term stability issues of PSCs ...remain a significant bottleneck impeding their commercialization. Inverted PSCs with a p-i-n architecture are being actively researched due to their concurrent good stability and decent efficiency. In particular, the PCE of inverted PSCs has improved significantly in recent years and is now almost approaching that of n-i-p PSCs. This review summarizes recent progress in the development of high-efficiency inverted PSCs, including the development of perovskite compositions, fabrication methods, and counter electrode materials (CEMs). Notably, we highlight the development of charge transport materials (CTMs) and the effects of defect passivation strategies on the performance of inverted PSCs. Finally, we discuss the remaining issues and perspectives of high-efficiency inverted PSCs.
The rapid progress of organic–inorganic metal halide perovskite solar cells (PSCs) has attracted broad interest in photovoltaic community. A typical PSC consists of anode/cathode, a perovskite layer ...as absorber, and carrier transport layer(s) (electron/hole transport layer(s)), which are stacked together, resulting in multi‐interfaces between these layers. Charge extraction and transport in these solar cell devices are strongly influenced by the interfaces and in particular the energy level alignment (ELA). It is the synergy of multiple interfaces and bulk films embedded in the cell architecture that has led to the extraordinary success of PSCs. Here, the authors review the progress of the studies on energy level alignment in PSCs, including several sections: methods for deriving ELA, semiconductor type of perovskite, bottom layer–dependent energy level shift of perovskite, density of states–governed ELA, ELA for specific interfaces, instability‐induced ELA variation, and defects and ion migration–induced ELA variation. Perspective and outlook for precisely determining ELA, designing the device architecture, and fabricating high performance PSCs are discussed.
Charge extraction and transport in perovskite solar cells (PSCs) are strongly influenced by the interfaces and in particular the energy level alignment (ELA). The recent advances of the research regarding energy level alignment in PSCs are reviewed. Perspective and outlook for precisely determining ELA, designing the device architecture, and fabricating high performance PSCs are discussed.
There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar cells (PSCs), but the current lead-free PSCs are still plagued with the critical issues of low ...efficiency and poor stability. This is primarily due to their inadequate photovoltaic properties and chemical stability. Herein we demonstrate the use of the lead-free, all-inorganic cesium tin-germanium triiodide (CsSn
Ge
I
) solid-solution perovskite as the light absorber in PSCs, delivering promising efficiency of up to 7.11%. More importantly, these PSCs show very high stability, with less than 10% decay in efficiency after 500 h of continuous operation in N
atmosphere under one-sun illumination. The key to this striking performance of these PSCs is the formation of a full-coverage, stable native-oxide layer, which fully encapsulates and passivates the perovskite surfaces. The native-oxide passivation approach reported here represents an alternate avenue for boosting the efficiency and stability of lead-free PSCs.
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