Morphology-photovoltaic property correlation in perovskite solar cells: One-step versus two-step deposition of CH3NH3PbI3

217

120

unexpectedly clean electronic properties of these semiconductors have led to the demonstration of proof-of-concept PV devices with an initial effi ciency that outperforms competing 'next-generation' technologies such as dye-sensitized, organic, and quantum dot solar cells, and even matches that of commercially deployed PV. [ 6 ] Other attractive characteristics of hybrid perovskites include the low embedded costs of materials processing and the ability to tune the properties of the semiconductor through changes in chemical composition. [ 1,[7][8][9][10] All of these factors have led to hybrid perovskites being considered as disruptive materials in a wide range of technology applications; [11][12][13][14][15][16] interest from the materials science research community is both substantial and rapidly maturing. Realizing the technology potential of hybrid perovskites necessitates a thorough understanding of the degradation mechanisms that limit the lifetime of devices, and identifying solutions to mitigate these. This exercise is nontrivial because of the various factors that can affect device performance: light, heat, moisture, oxygen, mechanical and electrical stresses, and combinations thereof. [ 17,18 ] Currently, perovskite solar cells (PSCs) based on the "triple layer" architecture with a thick carbon back electrode have demonstrated perhaps the most stable performance characteristics of all PSCs. [ 19 ] These devices, based on the mixed cation perovskite (5-AVA) X (MA) 1− X PbI 3 (where 5-AVA corresponds to 5-ammoniumvaleric acid), have been shown to maintain their initial power conversion effi ciency (PCE) of approximately 10% over 1000 h continuous simulated solar illumination, [ 20 ] dark storage for three months at elevated temperatures and humidity (85 °C/85%) and a minimum of 7 d operation in real-world conditions (Jeddah, Saudi Arabia). [ 21 ] Although clearly commendable, it is apparent that signifi cant work is required to realize PSCs with high stability and high performance, where promising stability metrics are combined with the certifi ed PCE values for champion devices. [ 22 ] To elucidate the underlying mechanisms for degradation in hybrid perovskites and guide the development of intrinsically stable devices, considerable work has been undertaken on the archetypal semiconductor of the research fi eld: CH 3 NH 3 PbI 3 . It is known that this material (and other single or mixed-halide derivatives) are particularly sensitive to moisture, [ 1,7,17,[23][24][25][26] where the proposed chemical reactions involving water result in decomposition of the perovskite into its precursor components via The rapid pace of development for hybrid perovskite photovoltaics has recently resulted in promising fi gures of merit being obtained with regard to device stability. Rather than relying upon expensive barrier materials, realizing market-competitive lifetimes is likely to require the development of intrinsically stable devices, and to this end accelerated aging tests can help identify degradation mechanisms tha...

Section: Resultsmentioning

confidence: 99%

Oxygen Degradation in Mesoporous Al₂O₃/CH₃NH₃PbI_3‐_xCl_x Perovskite Solar Cells: Kinetics and Mechanisms

Pearson

Eperon

Hopkinson

et al. 2016

217

120

“…As mentioned before, simple onestep methods often lead to inhomogeneous coverage of the substrates. [14,[102][103][104] In particular, Eperon et al studied the influence of the TiO 2 underlayer and its impact on perovskite-crystal formation when employing a non-stoichiometric mixture of MAI and PbCl 2 . They concluded that there is an www.advancedsciencenews.com unfavorable interaction between these layers, which leads to the growth of perovskite "pores", largely determined by the thickness of the perovskite film.…”

Section: One-step Depositionmentioning

confidence: 99%

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

Petrus

Schlipf

Cheng

et al. 2017

304

201

following statement: These materials can be processed from solution and yet exhibit optoelectronic materials properties described in classic solid-state physics textbooks. This unprecedented combination has led to photovoltaic devices that can be processed at room temperature and achieve performance levels similar to industry giant polycrystalline silicon, from a starting point of 3.8% in 2009. [1][2][3][4] The first light-emitting electrochemical cells [5] and diodes [6][7][8] have also been introduced recently, leading to tunable light emission spectra and internal quantum efficiencies exceeding 15%.The road towards these achievements has been marked by a constant improvement of perovskite deposition techniques fueled by our increasing understanding of the crystallization processes. The choice of deposition technique, either from solution or vapor, and the composition and order in which precursor species are applied has a great influence on the crystallization kinetics. Here, one can distinguish one-step methods where the perovskite is formed from a precursor mixture dissolved in a common solution, and two-step methods where the inorganic compound is deposited first and transformed to the perovskite phase later by addition of the organic constituents. [9][10][11] Furthermore, many parameters during processing can have an effect on the crystallization mechanism and consequently on film morphology, such as the choice of solvents, concentrations and processing additives that are often not incorporated into the final product. [11][12][13] We discuss this aspect in Section 2, where we focus our attention on the most commonly employed solution-based techniques. Additionally, as for any new technology trying to displace an incumbent technology, higher efficiencies, lower costs, reproducibility, stability, and sustainability are paramount. In particular, reproducibility has been a major challenge in perovskite solar cells from the beginning: small variations in morphology, like crystal size, film roughness, and pinholes can have detrimental effects on photovoltaic performance. [14] On the other hand, current-voltage measurements often showed a hysteresis that is rarely seen in other photovoltaic technologies. [15] These topics are highlighted in Sections 3 and 4. Finally, in Section 5 we discuss the framework for market introduction, such as cost reduction by choosing low-cost charge transport layers, or how the lifetime of perovskite absorbers can be extended by the choice of materials composition.Hybrid metal halide perovskites have become one of the hottest topics in optoelectronic materials research in recent years. Not only have they surpassed everyone's expectations and achieved similar performance as tried and true polycrystalline silicon photovoltaic devices, but they are also finding applications in a variety of different fields, including lighting. The main advantages of hybrid metal halide perovskites are simple processability, compatible with large-scale solution processing such as roll-to-roll printing, a...

“…[145,146] Two-step process based on the sequential deposition of inorganic and organic precursors, also adopts thermal annealing for perovskite crystal formation. [108,109,147,148] Bi et al investigated the effect of thermal annealing on structural, electrical, optical properties of MAPbI3 perovskite. [111] Noteworthy that thermal annealing works differently for perovskite films prepared from premixed solution and sequential deposition of inorganic/organic precursors.…”

Section: Heat Treatmentmentioning

confidence: 99%

Hybrid Perovskites: Effective Crystal Growth for Optoelectronic Applications

Jeon

Kim

Yoon

et al. 2017

Outstanding material properties of organic-inorganic hybrid perovskites have triggered a new research insight into the next-generation solar cells. Moreover, a wide range of controllable properties of hybrid perovskites particularly depending on crystal growth conditions enables versatile high performance optoelectronic devices such as light-emitting diodes, photodetectors and lasers beyond solar cells. This invited review article highlights recent progress of the crystallization strategies of organic-inorganic hybrid perovskites for effective light harvester or light emitter. In the first part, fundamental background on the perovskite crystalline structures and relevant optoelectronic properties such as optical band-gap, electron-hole behavior and energy band alignment are introduced. In the second part, detailed overview of the effective crystallization methods for perovskites, including thermal treatment, additives, solvent mediator, laser irradiation, nanostructure, crystal dimensionality and so on, is described to offer a comprehensive correlation among perovskite processing conditions, crystalline morphology and relevant device performances. Finally, future research direction is proposed to overcome current practical bottlenecks and move towards reliable high performance perovskite optoelectronic applications.3