Iodide manipulation using zinc additives for efficient perovskite solar minimodules.

Interstitial iodides are the most critical type of defects in perovskite solar cells that limits efficiency and stability. They can be generated during solution, film, and device processing, further accelerating degradation. Herein, we find that introducing a small amount of a zinc salt- zinc trifluoromethane sulfonate (Zn(OOSCF3)2) in the perovskite solution can control the iodide defects in resultant perovskites ink and films. CF3SOO̶ vigorously suppresses molecular iodine formation in the perovskites by reducing it to iodide. At the same time, zinc cations can precipitate excess iodide by forming a Zn-Amine complex so that the iodide interstitials in the resultant perovskite films can be suppressed. The perovskite films using these additives show improved photoluminescence quantum efficiency and reduce deep trap density, despite zinc cations reducing the perovskite grain size and iodide interstitials. The zinc additives facilitate the formation of more uniform perovskite films on large-area substrates (78-108 cm2) in the blade-coating process. Fabricated minimodules show power conversion efficiencies of 19.60% and 19.21% with aperture areas of 84 and 108 cm2, respectively, as certified by National Renewable Energy Laboratory (NREL), the highest efficiency certified for minimodules of these sizes.

Perovskite Quantum Dot Photovoltaic Materials beyond the Reach of Thin Films: Full-Range Tuning of A-Site Cation Composition.

We present a cation-exchange approach for tunable A-site alloys of cesium (Cs+) and formamidinium (FA+) lead triiodide perovskite nanocrystals that enables the formation of compositions spanning the complete range of Cs1- xFA xPbI3, unlike thin-film alloys or the direct synthesis of alloyed perovskite nanocrystals. These materials show bright and finely tunable emission in the red and near-infrared range between 650 and 800 nm. The activation energy for the miscibility between Cs+ and FA+ is measured (∼0.65 eV) and is shown to be higher than reported for X-site exchange in lead halide perovskites. We use these alloyed colloidal perovskite quantum dots to fabricate photovoltaic devices. In addition to the expanded compositional range for Cs1- xFA xPbI3 materials, the quantum dot solar cells exhibit high open-circuit voltage ( VOC) with a lower loss than the thin-film perovskite devices of similar compositions.

High-Performance Flexible Perovskite Solar Cells on Ultrathin Glass: Implications of the TCO.

For halide perovskite solar cells (PSCs) to fulfill their vast potential for combining low-cost, high efficiency, and high throughput production they must be scaled using a truly transformative method, such as roll-to-roll processing. Bringing this reality closer to fruition, the present work demonstrates flexible perovskite solar cells with 18.1% power conversion efficiency on flexible Willow Glass substrates. We highlight the importance of the transparent conductive oxide (TCO) layers on device performance by studying various TCOs. While tin-doped indium oxide (ITO) and indium zinc oxide (IZO) based PSC devices demonstrate high photovoltaic performances, aluminum-doped zinc oxide (AZO) based devices underperformed in all device parameters. Analysis of X-ray photoemission spectroscopy data shows that the stoichiometry of the perovskite film surface changes dramatically when it is fabricated on AZO, demonstrating the importance of the substrate in perovskite film formation.

Thermal engineering of FAPbI3 perovskite material via radiative thermal annealing and in situ XRD.

Lead halide perovskites have emerged as successful optoelectronic materials with high photovoltaic power conversion efficiencies and low material cost. However, substantial challenges remain in the scalability, stability and fundamental understanding of the materials. Here we present the application of radiative thermal annealing, an easily scalable processing method for synthesizing formamidinium lead iodide (FAPbI3) perovskite solar absorbers. Devices fabricated from films formed via radiative thermal annealing have equivalent efficiencies to those annealed using a conventional hotplate. By coupling results from in situ X-ray diffraction using a radiative thermal annealing system with device performances, we mapped the processing phase space of FAPbI3 and corresponding device efficiencies. Our map of processing-structure-performance space suggests the commonly used FAPbI3 annealing time, 10 min at 170 °C, can be significantly reduced to 40 s at 170 °C without affecting the photovoltaic performance. The Johnson-Mehl-Avrami model was used to determine the activation energy for decomposition of FAPbI3 into PbI2.