Chemical vapor deposited polymer layer for efficient passivation of planar perovskite solar cells

Reducing non-radiative recombination losses by advanced passivation strategies is pivotal to maximize the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Previously, polymers such as poly(methyl methacrylate), poly(ethylene oxide), and polystyrene were successfully applied in solution-processed passivation layers. However, controlling the thickness and homogeneity of these ultra-thin passivation layers on top of polycrystalline perovskite thin films is a major challenge. In response to this challenge, this work reports on chemical vapor deposition (CVD) polymerization of poly(p-xylylene) (PPX) layers at controlled substrate temperatures (14–16 °C) for efficient surface passivation of perovskite thin films. Prototype double-cation PSCs using a ∼1 nm PPX passivation layer exhibit an increase in open-circuit voltage (V$_{OC}$) of ∼40 mV along with an enhanced fill factor (FF) compared to a non-passivated PSC. These improvements result in a substantially enhanced PCE of 20.4% compared to 19.4% for the non-passivated PSC. Moreover, the power output measurements over 30 days under ambient atmosphere (relative humidity ∼40–50%) confirm that the passivated PSCs are more resilient towards humidity-induced degradation. Considering the urge to develop reliable, scalable and homogeneous deposition techniques for future large-area perovskite solar modules, this work establishes CVD polymerization as a novel approach for the passivation of perovskite thin films

Micron-scale rod-like scattering particles for light trapping in nanostructured thin film solar cells

Spherical dielectric particles, nanofibers, and nanorods have been widely used as embedded scattering objects in nanostructured thin film solar cells. Here we propose micron-scale rod-like dielectric particles as a more effective alternative to the spherical ones for light trapping in thin film solar cells. The superior performance of these micro-rods is attributed to their larger scattering efficiency relative to the spherical particles as evidenced by full-wave optical calculations. Using a one-pot process, 1.7 mu m-long bullet-shaped silica rods with 330 nm diameter are synthesized and their concentration in a N719-sensitized solar cell is optimized. A solar cell with an optimal concentration of rod-like particles delivers 8.74% power conversion efficiency (PCE), given the 6.33% PCE of the cell without any scattering particle. Moreover, a silver layer is deposited by chemical reduction of AgNO3 (Tollens' process) on the rear-side of the counter electrode, and hence the PCE of the optimal cell reaches 9.94%, showing 14% extra improvement due to the presence of the silver back-reflector. The rod-like scattering particles introduced here can be applied to other sensitized solar cells such as quantum-dot and organometallic perovskite solar cells

In Situ Methylammonium Chloride Assisted Perovskite Crystallization Strategy for High Performance Solar Cells

The optimization of perovskite crystallization is critical to achieving high performance perovskite solar cells PSCs . In the standard crystallization methods, the additives play an important role not only in optimizing the crystallization but also passivating the defect states of perovskite films. Methylammonium chloride MACl is one of the frequently used additives in this regard. However, the performance mechanism of MACl in the perovskite crystallization process still needs more investigation. This work presents the quality improvement of a perovskite film using MACl vapor as an external chlorine source. The in situ 2D GIXRD and real time X ray diffraction characterizations provide a better understanding the performance mechanism of MACl. Our results demonstrate that exposing the perovskite film to the MACl vapor during the crystallization process can effectively enhance the film quality in addition to enlarging the grain sizes. As a result, the MAPbI3 film optimized by our process leads to highly efficient PSCs with a power conversion efficiency PCE of amp; 8764;2

One-Step Thermal Gradient- and Antisolvent-Free Crystallization of All-Inorganic Perovskites for Highly Efficient and Thermally Stable Solar Cells.

All-inorganic perovskites have emerged as promising photovoltaic materials due to their superior thermal stability compared to their heat-sensitive hybrid organic-inorganic counterparts. In particular, CsPbI2 Br shows the highest potential for developing thermally-stable perovskite solar cells (PSCs) among all-inorganic compositions. However, controlling the crystallinity and morphology of all-inorganic compositions is a significant challenge. Here, a simple, thermal gradient- and antisolvent-free method is reported to control the crystallization of CsPbI2 Br films. Optical in situ characterization is used to investigate the dynamic film formation during spin-coating and annealing to understand and optimize the evolving film properties. This leads to high-quality perovskite films with micrometer-scale grain sizes with a noteworthy performance of 17% (≈16% stabilized), fill factor (FF) of 80.5%, and open-circuit voltage (VOC ) of 1.27 V. Moreover, excellent phase and thermal stability are demonstrated even after extreme thermal stressing at 300 °C

An Integrated Deposition and Passivation Strategy for Controlled Crystallization of 2D/3D Halide Perovskite Films

This work introduces a simplified deposition procedure for multidimensional (2D/3D) perovskite thin films, integrating a phenethylammonium chloride (PEACl)-treatment into the antisolvent step when forming the 3D perovskite. This simultaneous deposition and passivation strategy reduces the number of synthesis steps while simultaneously stabilizing the halide perovskite film and improving the photovoltaic performance of resulting solar cell devices to 20.8%. Using a combination of multimodal in situ and additional ex situ characterizations, it is demonstrated that the introduction of PEACl during the perovskite film formation slows down the crystal growth process, which leads to a larger average grain size and narrower grain size distribution, thus reducing carrier recombination at grain boundaries and improving the device's performance and stability. The data suggests that during annealing of the wet film, the PEACl diffuses to the surface of the film, forming hydrophobic (quasi-)2D structures that protect the bulk of the perovskite film from humidity-induced degradation

Coordination Chemistry as a Universal Strategy for a Controlled Perovskite Crystallization.

The most efficient and stable perovskite solar cells (PSCs) are made from a complex mixture of precursors. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor is initiated to trigger nucleation sites, e.g., by vacuum, an airstream, or a so-called antisolvent. Unfortunately, most oversaturation triggers do not expel the lingering (and highly coordinating) dimethyl sulfoxide (DMSO), which is used as a precursor solvent, from the thin films; this detrimentally affects long-term stability. In this work, (the green) dimethyl sulfide (DMS) is introduced as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, MAPbI3 PSCs are processed, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6% efficiency, among the highest reported efficiencies for this system. To confirm the universality of the strategy, DMS is tested for FAPbI3 as another composition, which shows higher efficiency of 23.5% compared to 20.9% for a device fabricated with chlorobenzene. This work provides a universal strategy to control perovskite crystallization using coordination chemistry, heralding the revival of perovskite compositions with pure DMSO

Roadmap on organic–inorganic hybrid perovskite semiconductors and devices

Metal halide perovskites are the first solution processed semiconductors that can compete in their functionality with conventional semiconductors, such as silicon. Over the past several years, perovskite semiconductors have reported breakthroughs in various optoelectronic devices, such as solar cells, photodetectors, light emitting and memory devices, and so on. Until now, perovskite semiconductors face challenges regarding their stability, reproducibility, and toxicity. In this Roadmap, we combine the expertise of chemistry, physics, and device engineering from leading experts in the perovskite research community to focus on the fundamental material properties, the fabrication methods, characterization and photophysical properties, perovskite devices, and current challenges in this field. We develop a comprehensive overview of the current state-of-the-art and offer readers an informed perspective of where this field is heading and what challenges we have to overcome to get to successful commercialization