An Efficient Approach to Fabricate Air-Stable Perovskite Solar Cells via Addition of a Self-Polymerizing Ionic Liquid

Despite the excellent photovoltaic properties achieved by perovskite solar cells at the laboratory scale, hybrid perovskites decompose in the presence of air, especially at high temperatures and in humid environments. Consequently, high-efficiency perovskites are usually prepared in dry/inert environments, which are expensive and less convenient for scale-up purposes. Here, a new approach based on the inclusion of an in situ polymerizable ionic liquid, 1,3-bis(4-vinylbenzyl)imidazolium chloride ([bvbim]Cl), is presented, which allows perovskite films to be manufactured under humid environments, additionally leading to a material with improved quality and long-term stability. The approach, which is transferrable to several perovskite formulations, allows efficiencies as high as 17% for MAPbI(3)processed in air % relative humidity (RH) >= 30 (from an initial 15%), and 19.92% for FAMAPbI(3)fabricated in %RH >= 50 (from an initial 17%), providing one of the best performances to date under similar conditions.

Investigation on the impact of passivation in perovskite solar cells

Erfan Shirzadi

Conversion of sunlight to electricity is the most plausible approach towards the generation of renewable energies. During recent decade lead halide perovskites (LHPs) have proven to be promising candidates for photovoltaic applications such as solar cells. LHPs can be made easily in laboratories around the world via solution process methods and many universities can afford to participate in their development. How-ever, LHPs suffer from instability issues and their efficiencies can be further improved. In this thesis, both instability and efficiency challenges are addressed. We showed by doping the precursor of methylammonium lead iodide (MAPbI3) perovskite with a relatively large cation of 2-Choloroethylammonium (CLEA), perovskites films with CLEA incorporated into their structures are formed. The novel perovskite is able to withstand high temperatures as high as 80°C while achieving efficiencies > 19% in MAPbI3-based perovskite solar cells (PSCs). Various approaches have been employed for the passivation of the defects in perovskite solar cells Vari-ous approaches have been employed to passivate the defects in perovskite films used in perovskite solar cells (PSCs). However, the passivation mechanism is often unclear at a molecular level and the reason for enhanced PSC performance remains elusive. Here, we describe passivation based on the deposition of two dimensional (2D) perovskites (obtained from para-halophenylethylammonium iodide) on the surface of perovskite films. Moreover, the mechanism of passivation was elucidated and was traced to the high work function of the 2D perovskites, which induce band-bending at the surface of perovskite film and therefore reduces the charge carrier recombination at the interface of perovskite and the hole transporting material (HTM). Efficiencies >22% with average voltages >1.15 V were achieved using a typical mesoporous-TiO2 and Spiro-OMeTAD device configuration. This study paves the way for PSCs efficiency improvement by rational design. The employment of 2D perovskites is a promising approach to tackle the stability and voltage issues inherent in perovskite solar cells. It remains unclear however whether other perovskites with different dimensionalities have the same effect on efficiency and stability. Here, we report the use of quasi-3D azetidinium lead iodide (AzPbI3) as a secondary layer on top of the primary 3D perovskite film that results in significant improvements in the photovoltaic parameters. Remarkably, utilization of AzPbI3 leads to the passivation resulting in a power conversion efficiency (PCE) of 22.4 %. The open-circuit voltage obtained is as high as 1.18 V, which is among the highest reported to date for single-junction perovskite solar cells, corresponding to a voltage deficit of 0.37 V for a bandgap of 1.55 eV. Studying the compositional instability of mixed ion perovskites under light illumination is important to understand the mechanisms underlying their efficiency and stability. However, current techniques are limited in resolution and are unable to deconvolute minor ion migration phenomena. Here, we describe a method that enables ion migration to be studied allowing different segregation mechanisms to be elucidated. We applied statistical analysis to cathodoluminescence data to generate compositional distribution histograms. Using these histograms, we identified two different ion migration phenomena, horizontal ion migration (HIM) and vertical ion migration (

EPFL2021

Intermediate phase engineering of halide perovskites for photovoltaics

Ulf Anders Hagfeldt, Zaiwei Wang, Wanchun Xiang, Jiahuan Zhang

Metal halide perovskites serving as one of the most promising photovoltaic materials are gaining considerable attention worldwide. For achieving high performance as well as long-term stability of the perovskite solar cells (PSCs), a good quality of perovskite film featuring in smooth, pinhole-free morphology, full coverage over substrates, good heterojunction contacts, and stable photoactive phase is of great importance. During solution fabrication for perovskite films, intermediate phase, which refers to the state of precursor composition before final annealing, plays an essential role in determining the film quality, especially in the state-of-theart PSCs. In this review, we summarize the research involving mechanism and applications of intermediate phase engineering (IPE) processes in various solution-processing technologies. The challenges of IPE are further discussed, and perspectives are provided for developing high-performance PSCs via IPE.

CELL PRESS2022

Auto-passivation of crystal defects in hybrid imidazolium/methylammonium lead iodide films by fumigation with methylamine affords high efficiency perovskite solar cells

Paul Joseph Dyson, Farzaneh Fadaei Tirani, Zhaofu Fei, Giulia Grancini, Xuehui Liu, Mohammad Khaja Nazeeruddin, Emadeddin Oveisi, Rosario Scopelliti, Erfan Shirzadi, Yi Zhang

Hybrid perovskite solar cells have attracted tremendous interest in the photovoltaic community. Despite their high defect tolerance, reducing the trap density by material engineering and surface modification is still critical to further boost performance. Here, methylammonium lead(II) iodide perovskite has been doped with imidazolium iodide in high concentrations (10-30 mol%) to boost solar cell performance, by passivating defects. Fumigation with methylamine results in the deprotonation of the embedded imidazolium cations, generating imidazole and methylammonium cations. The resulting (neutral) imidazole is extruded from the 3-D perovskite crystal and distributes around the crystal leading to auto-passivation of crystal defects. The structure of the imidazolium-PbI3 salt intermediate (i.e. formed in the absence of the methylammonium cation) has been determined and the resulting perovskite film characterized. Employed in solar cells, a power conversion efficiency (PCE) up to 20.14% is demonstrated.

2019

Investigation on the impact of passivation in perovskite solar cells

Erfan Shirzadi

EPFL2021