Query: Photovoltaic mixed-cation lead mixed-halide perovskites: links between crystallinity

Candidate papers:

abstract: Lead mixed halide perovskites are highly promising semiconductors for both multi junction photovoltaic and light emitting applications due to their tunable band gaps, with emission and absorption energies spanning the UV visible to near IR regions. However, many such perovskites exhibit unwanted halide segregation under photo illumination, the cause of which is still unclear. In our study, we establish crucial links between crystal phase stability, photostability and optoelectronic properties of the mixed cation lead mixed halide perovskite CsyFA(1 y)Pb(BrxI(1 x))3. We demonstrate a region for caesium content between 0.10 y 0.30 which features high crystalline quality, long charge carrier lifetimes and high charge carrier mobilities. Importantly, we show that for such high quality perovskites, photo induced halide segregation is strongly suppressed, suggesting that high crystalline quality is a prerequisite for good optoelectronic quality and band gap stability. We propose that regions of short range crystalline order aid halide segregation, possibly by releasing lattice strain between iodide rich and bromide rich domains. For an optimized caesium content, we explore the orthogonal halide variation parameter space for Cs0.17FA0.83Pb(BrxI(1 x))3 perovskites. We demonstrate excellent charge carrier mobilities (11 40 cm2 V 1 s 1) and diffusion lengths (0.8 4.4 mm) under solar conditions across the full iodide bromide tuning range. Therefore, the addition of caesium yields a more photo stable perovskite system whose absorption onsets can be tuned for bandgap optimized tandem solar cells.
author_names: Waqaas Rehman

David P McMeekin

Jay B Patel

Rebecca L Milot

Michael B Johnston

Henry J Snaith

Laura M Herz
title: Photovoltaic mixed cation lead mixed halide perovskites: links between crystallinity, photo stability and electronic properties
year: 2017

abstract: Perovskites for tandem solar cells Improving the performance of conventional single crystalline silicon solar cells will help increase their adoption. The absorption of bluer light by an inexpensive overlying solar cell in a tandem arrangement would provide a step in the right direction by improving overall efficiency. Inorganic organic perovskite cells can be tuned to have an appropriate band gap, but these compositions are prone to decomposition. McMeekin et al. show that using cesium ions along with formamidinium cations in lead bromide iodide cells improved thermal and photostability. These improvements lead to high efficiency in single and tandem cells. Science, this issue p. 151 Addition of cesium cations creates a robust ideal inorganic organic perovskite absorber for tandem silicon solar cells. Metal halide perovskite photovoltaic cells could potentially boost the efficiency of commercial silicon photovoltaic modules from ~20 toward 30% when used in tandem architectures. An optimum perovskite cell optical band gap of ~1.75 electron volts (eV) can be achieved by varying halide composition, but to date, such materials have had poor photostability and thermal stability. Here we present a highly crystalline and compositionally photostable material, [HC(NH2)2]0.83Cs0.17Pb(I0.6Br0.4)3, with an optical band gap of ~1.74 eV, and we fabricated perovskite cells that reached open circuit voltages of 1.2 volts and power conversion efficiency of over 17% on small areas and 14.7% on 0.715 cm2 cells. By combining these perovskite cells with a 19% efficient silicon cell, we demonstrated the feasibility of achieving >25% efficient four terminal tandem cells.
author_names: David P McMeekin

Golnaz Sadoughi

Waqaas Rehman

Giles E Eperon

Michael Saliba

Maximilian T Horantner

Amir A Haghighirad

Nobuya Sakai

Lars Korte

Bernd Rech

Michael B Johnston

Laura M Herz

Henry J Snaith
title: A mixed cation lead mixed halide perovskite absorber for tandem solar cells
venue: Science
year: 2016

abstract: Mixed halide lead perovskites are becoming of paramount interest in the optoelectronic and photovoltaic research fields, offering band gap tunability, improved efficiency, and enhanced stability compared to their single halide counterparts. Formamidinium based mixed halide perovskites (FA MHPs) are critical to obtaining optimum solar cell performance. Here, we report a solvent free mechanochemical synthesis (MCS) method to prepare FA MHPs, starting with their parent compounds (FAPbX3; X Cl, Br, I) achieving compositions not previously accessible through the solvent synthesis (SS) technique. By probing local Pb environments in MCS FA MHPs using solid state nuclear magnetic resonance spectroscopy, along with powder X ray diffraction for long range crystallinity and reflectance measurements to determine the optical band gap, we show that MCS FA MHPs form atomic level solid solutions between Cl/Br and Br/I MHPs. Our results pave the way for advanced methods in atomic level structural understanding while offering a one pot synthetic approach to prepare MHPs with superior control of stoichiometry.
author_names: Abdelrahman M Askar

Abhoy Karmakar

Guy M Bernard

Michelle Ha

Victor V Terskikh

Benjamin D Wiltshire

Sahil D Patel

Jonathan Fleet

Karthik Shankar

Vladimir K Michaelis
title: Composition Tunable Formamidinium Lead Mixed Halide Perovskites via Solvent Free Mechanochemical Synthesis: Decoding the Pb Environments Using Solid State NMR Spectroscopy.
venue: The journal of physical chemistry letters
year: 2018

abstract: Mixed halide perovskites have attracted a strong interest in the photovoltaic community as a result of their high power conversion efficiency and the solid opportunity to realise a low cost and industry scalable technology. Light soaking represents one of the most promising approach to reduce non radiative recombination processes and thus to optimise device performances. Here, we investigate the effects of 1 sun illumination on state of the art triple cation halide perovskite thin films Cs0.05(MA0.14, FA0.86)0.95 Pb (I0.84, Br0.16) by a combined optical and chemical characterization. Competitive passivation and degradation effects on perovskite transport properties have been analyzed by spectrally and time resolved quantitative imaging luminescence analysis and by X ray photoemission spectroscopy (XPS) We notice a clear improvement of the optoelectronic properties of the material, with a net increase of the Quasi Fermi Level Splitting and a corresponding decrease of methylammonium MA+ for short (up to one hour) light soaking time. However, after 5 hours of light soaking phase segregation and in depth oxygen penetration lead to a decrease of the charge mobility.
author_names: Stefania Cacovich

Davina Messou

Adrien Bercegol

Solene Bechu

Armelle Yaiche

Hamza Shafique

J -G Rousset

Philip Schulz

Muriel Bouttemy

Laurent Lombez
title: Light Induced Passivation in Triple Cation Mixed Halide Perovskites: Interplay between Transport Properties and Surface Chemistry.
venue: ACS applied materials interfaces
year: 2020

abstract: Organic inorganic lead halide perovskites containing a mixture of iodide and bromide anions consistently perform better in donor acceptor heterojunction solar cells than the standard methylammonium lead triiodide material. This observation is counterintuitive, as it is generally expected for photovoltaic materials that heterogeneities and compositional disorder cause reduced carrier diffusion length and conversion efficiency. Here, we combine ultrafast photoinduced electroabsorption and broadband fluorescence up conversion spectroscopy measurements to scrutinize the carrier dynamics in mixed cations, mixed halide lead perovskite thin films. Our results evidence the formation of charge transfer excitons (CTE) across the boundaries of domains of various halide compositions. A global analysis of photoinduced transient Stark signals shows that CTE evolve gradually from Br rich to I rich domains over tens to hundreds of picoseconds. Rather than constituting recombination centres, boundaries between domains of various halide compositions appear then to favour charge carrier separation by driving photogenerated holes along channels of decreasing bromide content.
author_names: Marine E F Bouduban

Fabrizio Giordano

Arnulf Rosspeintner

Joel Teuscher

Eric Vauthey

Michael Gratzel

Jacques-E Moser
title: Inter Domain Charge Transfer as a Rationale for Superior Photovoltaic Performances of Mixed Halide Lead Perovskites
year: 2018

abstract: Tin halide perovskites are promising candidates for lead free photovoltaic and optoelectronic materials, but not all of them have been well characterized. It is essential to determine how the bulk photophysical properties are correlated with their structures at both short and long ranges. Although CsSnCl3 is normally stable in the cubic perovskite structure only above 379 K, it was prepared as a metastable phase at room temperature. The transition from the cubic to the monoclinic phase, which is the stable form at room temperature, was tracked by solid state 133Cs NMR spectroscopy and shown to take place through a first order kinetics process. The complete solid solution CsSn(Cl1 xBrx)3 (0 x 1) was successfully prepared, exhibiting cubic perovskite structures extending between the metastable CsSnCl3 and stable CsSnBr3 end members. The NMR spectra of CsSnBr3 samples obtained by three routes (high temperature, mechanochemical, and solvent assisted reactions) show distinct chemical shift ranges, spin lattice relaxation parameters and peak widths, indicative of differences in local structure, defects and degree of crystallinity within these samples. Variable temperature 119Sn spin lattice relaxation measurements reveal spontaneous mobility of Br atoms in CsSnBr3. The degradation of CsSnBr3, exposed to an ambient atmosphere for nearly a year, was monitored by NMR spectroscopy and powder X ray diffraction, as well as by optical absorption spectroscopy.
author_names: Abhoy Karmakar

A J Bhattacharya

Diganta Sarkar

Guy M Bernard

Arthur Mar

Vladimir K Michaelis
title: Influence of hidden halogen mobility on local structure of CsSn(Cl1 xBrx)3 mixed halide perovskites by solid state NMR+
venue: Chemical science
year: 2020

abstract: Managing defects in SnO2 is critical for improving the power conversion efficiency (PCE) of halide perovskite based solar cells. However, typically reported SnO2 based perovskite solar cells have inherent defects in the SnO2 layer, which lead to a lower PCE and hysteresis. Here, we report that a dual coating approach for SnO2 with different annealing temperatures can simultaneously form a SnO2 layer with high crystallinity and uniform surface coverage. Along with these enhanced physical properties, the dual coated SnO2 layer shows favorable band alignment with a mixed halide perovskite. After careful optimization of the dual coating method, the average PCE of the perovskite solar cell based on the dual coated SnO2 layer increases from 18.07% to 19.23% with best performing cell of 20.03% Note that a facile two step coating and annealing method can open new avenues to develop SnO2 based perovskite solar cells with stabilized and improved photovoltaic performances.
author_names: Jung Hwan Lee

Dongguen Shin

Ryan Rhee

Sang Geun Yun

Kyung Mun Yeom

Do Hyung Chun

Sunje Lee

Dongho Kim

Yeonjin Yi

Jun Hong Noh

Jong Hyeok Park
title: Band Alignment Engineering between Planar SnO2 and Halide Perovskites via Two Step Annealing.
venue: The journal of physical chemistry letters
year: 2019

abstract: Due to their high power conversion efficiency, organic inorganic lead halide perovskites have emerged as promising materials for next generation solar cell devices. As the efficiency race continues for this revolutionary class of light harvesting materials, many questions about the structural, electronic and optical properties of perovskite solar cells have still to be addressed. More particularly, the long term stability of this kind of devices is an open question because various different crystalline phases exist in a narrow temperature range.[1] Mixed cation lead halide perovskites have attracted wide attention due to the possibility of tackling the problem of limited phase stability. Through a theoretical analysis of the phase stability of binary formamidinium (FA) rich, cesiumrich FA/Cs and guanidinium (GUA)/FA mixtures as well as ternary Cs/GUA/FA mixtures, we propose a series of design principles for the synthesis of stable mixed cation lead halide perovskites that could be potential candidates for solar cell applications.[2] In addition to this, an understanding of the correlations between different photophysical properties and the atomistic characteristics of these materials is paving the way for the design of lead halide perovskites with enhanced optical properties.[3] For this reason, the anomalous low temperature behavior of the photoluminescence spectra of cesium lead bromide is rationalized in terms of the structural characteristics of the material at low temperatures.
author_names: Ariadni Boziki
title: Computational studies of the structural and optical properties of organic inorganic lead halide perovskites.
year: 2019

abstract: Quasi two dimensional (2D) mixed cation hybrid halide perovskites (A'2AN 1MNX3N+1; A' large organic molecule with cationic group, A [Cs+ CH3NH3+ HC(NH2)2+ M [Pb, Sn, Ge] X [I Br Cl have rapidly emerged as candidates to improve the structural stability and device lifetime of 3D perovskite semiconductor devices under operating conditions. The addition of the large A' cation to the traditional AMX3 structure introduces several synthetic degrees of freedom and breaks M X bonds, giving rise to peculiar critical phase behavior in the phase space of these complex materials. In this work, we propose a thermodynamic model parametrized by first principles calculations to generate the phase diagram of 2D and quasi 2D perovskites (q 2DPKs) based on the mechanics and electrostatics of the interface between the A' cations and the metal halide octahedral network. Focusing on the most commonly studied methylammonium lead iodide system where A' is n butylammonium (BA; CH3(CH2)3NH3+ we find that the apparent difficulty in synthesizing phase pure samples with a stoichiometric index N 5 can be attributed to the energetic competition between repulsion of opposing interfacial dipole layers and mechanical relaxation induced by interfacial stress. Our model shows quantitative agreement with experimental observations of the maximum phase pure stoichiometric index (Ncrit) and explains the non monotonic evolution of the lattice parameters with increasing stoichiometric index (N) This model is generalizable to the entire family of q 2DPKs and can guide the design of photovoltaic and optical materials that combine the structural stability of the q 2DPKs while retaining the charge carrier properties of their 3D counterparts.
author_names: Christopher C Price

Jean-Christophe Blancon

Aditya D Mohite

Vivek B Shenoy
title: Interfacial Electromechanics Predicts Phase Behavior of 2D Hybrid Halide Perovskites.
venue: ACS nano
year: 2020

abstract: The development of smart illumination sources represents a central challenge for current technology. In this context, the quest for novel materials that enable efficient light generation is essential. Metal halide compounds with perovskite crystalline structure (ABX3) have gained tremendous interest in the last five years since they come as easy to prepare high performance semiconductors. Perovskite absorbers are driving the power conversion efficiencies of thin film photovoltaics to unprecedented values. Nowadays, mixed cation, mixed halide lead perovskite solar cells reach efficiencies consistently over 20% and promise to get close to 30% in multijunction devices when combined with silicon cells at no surcharge. Nonetheless, perovskites' fame extends further since extensive research on these novel semiconductors has also revealed their brightest side. Soon after their irruption in the photovoltaic scenario, demonstration of efficient color tunable with high color purity perovskite emitters has opened new avenues for light generation applications that are timely to discuss herein.
author_names: Gabriel Lozano
title: The Role of Metal Halide Perovskites in Next Generation Lighting Devices
venue: The journal of physical chemistry letters
year: 2018