Interfaces in Perovskite Solar Cells Fakharuddin, Azhar; Schmidt‐Mende, Lukas; Garcia‐Belmonte, Germà ...
Advanced energy materials,
November 22, 2017, Letnik:
7, Številka:
22
Journal Article
Recenzirano
Odprti dostop
Rapid improvement in photoconversion efficiency (PCE) of solution processable organometallic hybrid halide based perovskite solar cells (PSCs) have taken the photovoltaic (PV) community with a ...surprise and has extended their application in other electronic devices such as light emitting diodes, photo detectors and batteries. Together with efforts to push the PCE of PSCs to record values >22% – now at par with that of crystalline silicon solar cells – origin of their PV action and underlying physical processes are also deeply investigated worldwide in diverse device configurations. A typical PSC consists of a perovskite film sandwiched between an electron and a hole selective contact thereby creating ESC/perovskite and perovskite/HSC interfaces, respectively. The selective contacts and their interfaces determine properties of perovskite layer and also control the performance, origin of PV action, open circuit voltage, device stability, and hysteresis in PSCs. Herein, we define ideal charge selective contacts, and provide an overview on how the choice of interfacing materials impacts charge accumulation, transport, transfer/recombination, band‐alignment, and electrical stability in PSCs. We then discuss device related considerations such as morphology of the selective contacts (planar or mesoporous), energetics and electrical properties (insulating and conducting), and its chemical properties (organic vs inorganic). Finally, the outlook highlights key challenges and future directions for a commercially viable perovskite based PV technology.
The past few years marked a new era of organometallic halide hybrid perovskite efficient solar cell technology. To capitalize the potential of this new class of materials in solar cells, in particular, and in any electronic devices in general, an understanding of interfacial physical processes is crucial. Herein, a comprehensive analysis of the role of interfaces in determining the PV performance and long term operational stability of this PV technology is provided.
Organic–inorganic halide perovskites are making breakthroughs in a range of optoelectronic devices. Reports of >23% certified power conversion efficiency in photovoltaic devices, external quantum ...efficiency >21% in light‐emitting diodes (LEDs), continuous‐wave lasing and ultralow lasing thresholds in optically pumped lasers, and detectivity in photodetectors on a par with commercial GaAs rivals are being witnessed, making them the fastest ever emerging material technology. Still, questions on their toxicity and long‐term stability raise concerns toward their market entry. The intrinsic instability in these materials arises due to the organic cation, typically the volatile methylamine (MA), which contributes to hysteresis in the current–voltage characteristics and ion migration. Alternative inorganic substitutes to MA, such as cesium, and large organic cations that lead to a layered structure, enhance structural as well as device operational stability. These perovskites also provide a high exciton binding energy that is a prerequisite to enhance radiative emission yield in LEDs. The incorporation of inorganic and layered perovskites, in the form of polycrystalline films or as single‐crystalline nanostructure morphologies, is now leading to the demonstration of stable devices with excellent performance parameters. Herein, key developments made in various optoelectronic devices using these perovskites are summarized and an outlook toward stable yet efficient devices is presented.
Inorganic and layered perovskites have broadened research paradigm for a range of optoelectronic devices. Their unique electronic and photophysical properties show that they are an excellent material, leading forefronts of solar cells, light‐emitting diodes, photodetectors, lasers, and beyond. An overview of key research activities for these devices is provided and challenges for their future research are identified.
Perovskite light emitting diodes (PeLEDs) have reached external quantum efficiencies (EQEs) over 21%. Their EQE, however, drops at increasing current densities (J) and their lifetime is still limited ...to just a few hours. The mechanisms leading to EQE roll‐off and device instability require thorough investigation. Here, improvement in EQE, EQE roll‐off, and lifetime of PeLEDs is demonstrated by tuning the balance of electron/hole transport into a mixed 2D/3D perovskite emissive layer. The mixed 2D/3D perovskite layer induces exciton confinement and beneficially influences the electron/hole distribution inside the perovskite layer. By tuning the electron injection to match the hole injection in such active layer, a nearly flat EQE for J = 0.1–200 mA cm−2, a reduced EQE roll‐off until J = 250 mA cm−2, and a half‐lifetime of ≈47 h at J = 10 mA cm−2 is reached. A model is also proposed to explain these improvements that account for the spatial electron/hole distributions.
Improvement in external quantum efficiency (EQE), EQE roll‐off, and lifetime of perovskite light emitting diodes is demonstrated by balancing electron and hole transport/injection into the perovskite emissive layer and perovskite compositional engineering. Charge injection balance together with optimized 2D/3D perovskite stoichiometry leads to nearly flat EQE over a wide current range and lifetime of several tens of hours under continuous operation.
Perovskite solar cells employing CH3NH3PbI3–x Cl x active layers show power conversion efficiency (PCE) as high as 20% in single cells and 13% in large area modules. However, their operational ...stability has often been limited due to degradation of the CH3NH3PbI3–x Cl x active layer. Here, we report a perovskite solar module (PSM, best and av. PCE 10.5 and 8.1%), employing solution-grown TiO2 nanorods (NRs) as the electron transport layer, which showed an increase in performance (∼5%) even after shelf-life investigation for 2500 h. A crucial issue on the module fabrication was the patterning of the TiO2 NRs, which was solved by interfacial engineering during the growth process and using an optimized laser pulse for patterning. A shelf-life comparison with PSMs built on TiO2 nanoparticles (NPs, best and av. PCE 7.9 and 5.5%) of similar thickness and on a compact TiO2 layer (CL, best and av. PCE 5.8 and 4.9%) shows, in contrast to that observed for NR PSMs, that PCE in NPs and CL PSMs dropped by ∼50 and ∼90%, respectively. This is due to the fact that the CH3NH3PbI3–x Cl x active layer shows superior phase stability when incorporated in devices with TiO2 NR scaffolds.
High efficiency is routinely reported in CH3NH3PbI3−xClx sensitized mesoscopic solar cells (PSCs) employing planar and scaffold architectures; however, a systematic comparison of their photovoltaic ...performance under similar experimental conditions and their long term stability have so far not been discussed. In this paper, we compare the performance and durability of PSCs employing these two device configurations and conclude that although a planar architecture routinely provides high initial photoconversion efficiency (PCE), particularly high open-circuit voltage (VOC), a scaffold is crucial to achieve long term durable performance of such devices. In a comparative study of scaffold (rutile nanorods, NRs) vs. planar devices, the efficiency in latter dropped off by one order of magnitude in ∼300 h despite their similar initial PCE of ∼12%. We compared the performance and the durability of two types of scaffolds, i.e., pristine and TiCl4 treated NRs, and observed that the pristine NRs showed >10% improvement in the PCE after ∼1300 h whereas the cells employing post-treated NR scaffold retained ∼60% of initial value. We address the origin of the different photovoltaic performance of planar and scaffold devices in the context of photoanode morphology and its possible effect on the cell durability.
A planar architecture routinely provides high initial photoconversion efficiency however a scaffold is crucial to achieve long term durable performance of perovskite solar cells as the morphology and crystallinity of the electron transport layer have its significant affect on their long term operational stability. Display omitted
•High efficiency perovskite solar cells with planar and scaffold architectures are developed.•The rutile nanorods devices reached a photoconversion efficiency ∼12.2%, a record for this type till date.•TiCl4 post-treatment of nanorod cells resulted in simultaneously increase of the JSC and VOC.•The long term performance of the planar and scaffold devices is compared for the first time.•Performance stability is related to crystallinity and chemical stability of the scaffold layer.
Perovskite solar cells (PSCs) have achieved certified power conversion efficiency (PCE) over 25%. Though their high PCE can be achieved by optimizing absorber layer and device interfaces, the ...intrinsic instability of perovskite materials is still a key issue to be resolved. Mixed‐halide perovskites using multiple halogen constituents have been proved to improve robustness; however, the anion at the X site in the ABX3 formula is not limited to halogens. Other negative monovalent ions with similar properties to halogens, such as pseudo‐halogens, have the opportunity to form perovskites with ABX3 stoichiometry. Recently, thiocyanates and formates have been utilized to synthesize stable perovskite materials. This review presents the evolution of pseudo‐halide perovskite solar cells in the past few years. The intrinsic properties, their effects on crystal structure, and bandgap engineering of the pseudo‐halide perovskites are summarized. Various thiocyanate compounds applied in the fabrication of perovskite solar cells are discussed. The fabrication process, film formation mechanism, and crystallinity of pseudo‐halide perovskites are elucidated to understand their effects on the photovoltaic performance and device stability. Other applications of pseudo‐halide perovskites are summarized in the final section. Lastly, this review concludes with suggestions and outlooks for further research directions.
Monovalent pseudo‐halide anions share similar properties to halide anions. This review presents the evolution of pseudo‐halide perovskite solar cells in the past few years. The role of pseudo‐halides and their position and occupation in perovskite crystal, its impact on perovskite film quality, solar cell stability and photovoltaic performance, and pseudo‐halide optoelectronic devices beyond solar cells are compared comprehensively.
Interfacial engineering has shown to play an essential role to optimize recombination losses in perovskite solar cells; however, an in-depth understanding of the various loss mechanisms is still ...underway. Herein, we study the charge transfer process and reveal the primary recombination mechanism at inorganic electron-transporting contacts such as TiO2 and its modified organic rivals. The modifiers are chemically (6,6-phenyl C61 butyric acid, PC60BA) or physically (6,6-phenyl C61 butyric acid methyl ester, PC60BM and C60) attached fullerene to the TiO2 surface to passivate the density of surface states. We do not observe any change in morphology, crystallinity, and bulk defect density of halide perovskite (CH3NH3PbI3 in this case) upon interface modification. However, we observe compelling results via photoluminescence and electroluminescence studies that the recombination dynamics at both time scales (slow and fast) are largely influenced by the choice of the selective contact. We note a strong correlation between the hysteresis and the so-called slow charge dynamics, both significantly influenced by the characteristics of the selective contact, for example, the presence of surface traps at the selective contact not only shows a larger hysteresis but also leads to higher charge accumulation at the interface and distinguishable slow dynamics (a slower stabilization of recombination dynamics at a time scale of several minutes).
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