Highly Efficient and Stable 2D Dion Jacobson/3D Perovskite Heterojunction Solar Cells

Heterostructures involving two-dimensional/three-dimensional (2D/3D) perovskites have recently attracted increased attention due to their ability to combine the high photovoltaic performance of 3D perovskites with the increased stability of 2D perovskites. Here we report ammonium thiocyanate (NH4SCN) passivated 3D methylammonium lead triiodide (MAPbI(3)) perovskite active layer and deposition of 2D perovskite capping layer using xylylene diammonium iodide (XDAI) organic cation. The 2D/3D perovskite heterojunction formation is probed by using FESEM and UPS spectroscopy. The NH4SCN passivated MAPbI(3) perovskite has shown 19.6% PCE compared to the 17.18% PCE of pristine MAPbI(3) perovskite solar cells (PSCs). Finally, the champion 2D/3D perovskite heterojunction based solar cells have achieved the remarkable PCE of 20.74%. The increased PCE in 2D/3D PSCs is mainly attributed to the reduced defect density and suppressed nonradiative recombination losses. Moreover, the hydrophobic 2D capping layer endows the 2D/3D heterojunction perovskites with exceptional moisture, thermal and UV stability, highlighting the promise of highly stable and efficient 2D/3D PSCs.

A review on two-dimensional (2D) and 2D-3D multidimensional perovskite solar cells: Perovskites structures, stability, and photovoltaic performances

Mohammad Khaja Nazeeruddin

Perovskite solar cells (PSCs) fabricated with two-dimensional (2D) halide and 2D-3D mixed-halide materials are remarkable for their optoelectronic properties. The 2D perovskite structures are extremely stable but show limited charge transport and large bandgap for solar cell applications. To overcome these challenges, multidi-mensional 2D-3D perovskite materials are used to maintain simultaneously, a long-term stability, and high performance. In this review, we discuss the recent progress and the advantages of 2D and 2D-3D perovskite materials as absorber for solar cell applications. First, we discuss the structure and the unique properties of 2D and multidimensional 2D-3D perovskites materials. Second, the stability of 2D and 2D-3D mixed perovskites and the perspects of PSCs are hashed out.

ELSEVIER2021

The effect of illumination on the formation of metal halide perovskite films

Antonio Abate, Taisuke Matsui, Jiyoun Seo, Ludmilla Steier, Wolfgang Richard Tress, Amita Ummadisingu

Optimizing the morphology of metal halide perovskite films is an important way to improve the performance of solar cells(1) when these materials are used as light harvesters(2), because film homogeneity is correlated with photovoltaic performance(3). Many device architectures and processing techniques have been explored with the aim of achieving high-performance devices(4), including single-step deposition(5), sequential deposition(6,7) and anti-solvent methods(1,8). Earlier studies have looked at the influence of reaction conditions on film quality(3), such as the concentration of the reactants9,10 and the reaction temperature(11). However, the precise mechanism of the reaction and the main factors that govern it are poorly understood. The consequent lack of control is the main reason for the large variability observed in perovskite morphology and the related solar-cell performance(2,3). Here we show that light has a strong influence on the rate of perovskite formation and on film morphology in both of the main deposition methods currently used: sequential deposition and the anti-solvent method. We study the reaction of a metal halide (lead iodide) with an organic compound (methylammonium iodide) using confocal laser scanning fluorescence microscopy and scanning electron microscopy. The lead iodide crystallizes before the intercalation of methylammonium iodide commences, producing the methylammonium lead iodide perovskite. We find that the formation of perovskite via such a sequential deposition is much accelerated by light. The influence of light on morphology is reflected in a doubling of solar-cell efficiency. Conversely, using the anti-solvent method to form methyl ammonium lead iodide perovskite in a single step from the same starting materials, we find that the best photovoltaic performance is obtained when films are produced in the dark. The discovery of light-activated crystallization not only identifies a previously unknown source of variability in opto-electronic properties, but also opens up new ways of tuning morphology and structuring perovskites for various applications.

Nature Publishing Group2017

Fundamentals of perovskite formation for photovoltaics

Amita Ummadisingu

Perovskite solar cells have become strong contenders in the arena of photovoltaics due to the stunning rise in their efficiency from 3 % to over 20 % in just seven years. In this time, numerous device architectures and thin film deposition methods have been explored. The sequential deposition and anti-solvent methods are among the most widely used for preparing perovskite solar cells. Optimizing these perovskite deposition processes to tune the perovskite film morphology plays a key role in the race for the highest efficiencies as homogeneity of the film correlates with superior photovoltaic performance. To date, the factors controlling perovskite film formation in various deposition methods and the precise mechanism are little understood. In light of this, the aim of the thesis is to unravel the salient aspects of perovskite film formation. I first study the formation of methylammonium lead iodide in sequential deposition using confocal laser scanning fluorescence microscopy (CLSM) and scanning electron microscopy (SEM). I discover that illumination during film formation is a major factor in the reaction as it greatly accelerates perovskite formation and tunes the final film morphology by controlling nucleation of lead iodide. The nucleation density increases logarithmically with the illumination intensity. I uncover the mechanism behind this effect and demonstrate that it is a quantum phenomenon and not merely a heating effect. I posit that absorbed light lowers the surface tension, thereby facilitating nucleation. Not only is this effect present in the main deposition methods â sequential deposition and the anti-solvent methods, but also in perovskites of more complex compositions that are employed in state-of-the-art solar cells. Second, I scrutinize the individual stages in the formation of methylammonium lead iodide perovskite in sequential deposition. SEM-cathodoluminescence imaging identifies the presence of mixed crystalline aggregates composed of methylammonium lead iodide perovskite and lead iodide in forming perovskite films. Using cross-sectional CLSM for the first time, I identify the directionality of perovskite formation. Kinetic monitoring and model fitting bring forward the Avrami models as the most suitable to quantify and represent the formation of perovskite under different conditions of temperature, film thickness and illumination. Finally, I identify a maturation effect in the perovskite film in solar cells stored in the dark and investigate the dynamic spontaneous coalescence of crystals in the film. During maturation, small crystals merge to form larger ones and this reduces the number of grain boundaries and the associated trap states, supressing non-radiative recombination. The photovoltaic performance of high efficiency solar cells thus increases and it is accompanied by a reduction in the hysteresis. Overall, apart from providing insights into the dynamic nature of deposited films, I present a fundamental understanding of the perovskite formation process in different deposition methods and for various compositions. Such a comprehensive picture aids in the achievement of high photovoltaic performance.