Ammonium Additive Engineering in Antisolvents for Improving Perovskite/Charge-Transport-Layer Interfaces toward Efficient Lead-Tin Alloyed Perovskite Solar Cells.

Although significant advancements have been achieved in lead-tin (Pb-Sn) alloyed perovskite solar cells (PSCs), their power conversion efficiency (PCE) remains inferior to that of their Pb-based counterparts, primarily due to higher open-circuit voltage (Voc) losses and lower fill factors (FFs). Herein, we report both perovskite top and bottom interfacial improvements by incorporating a facile fluorophenylethylammonium iodide (p-FPEAI)/ethyl acetate (EA) solution during the film crystal growth. Based on the analysis of perovskite crystallization, film growth, and strain relaxation, the mechanisms behind these interfacial improvements have been well understood. Furthermore, p-FPEAI could reduce the defect density and nonradiative recombination losses, thus attributing to the improved Voc and FF. Finally, the treated device achieved a PCE of 20.14% with a Voc of up to 0.84 V, which is among the highest reported values so far for Pb-Sn alloyed PSCs without additional precursor additives. In addition, the unencapsulated p-FPEAI-treated device maintained its initial efficiency of approximately 92% after being kept in a nitrogen atmosphere for 1 month, in contrast to the control device which retained only 30% of its initial value. Our findings provide a comprehension for understanding the effect of bulky cations as antisolvents on fabricating highly efficient Pb-Sn alloyed perovskite solar cells.

Regulating crystallization dynamics and crystal orientation of methylammonium tin iodide enables high-efficiency lead-free perovskite solar cells.

Tin (Sn)-based perovskite solar cells (PSCs) have attracted much attention because they are more environmentally friendly than lead-based PSCs. However, the fast crystallization of Sn-based perovskite films and the easy oxidation of Sn2+ to Sn4+ hinder the improvement of their efficiency and stability. In this work, ethylammonium bromide (EABr) was added to methylammonium tin iodide (MASnI3) perovskite precursor solution to regulate the crystallization dynamics and improve the film morphology. The results show that the large EA+ ions slow down the crystallization process of Sn-based perovskites and form a smooth perovskite film with high crystallinity, while the added Br- anions further improved the crystallinity and orientation of the perovskite film. Under the combined action of EA+ and Br- ions, the as-produced PSCs achieved a champion power conversion efficiency (PCE) of 9.59%. The EABr additive also retarded the oxidation of Sn2+, and the solar cell device maintained 93% of its initial efficiency after 30 days in a nitrogen-filled glove box without being encapsulated. This work provides a new strategy for the realization of high-efficiency Sn-based PSCs.

Low-temperature processed inorganic perovskites for flexible detectors with a broadband photoresponse.

Flexible photodetectors (PDs) have become a research hotspot due to their potential applications in foldable displays, wearable optoelectronic devices, and implantable biomedical sensors. Inorganic CsPbBr3 perovskites, an emerging class of stable metal halide perovskites, have been explored as photoactive materials in PDs due to their superior photoelectrical properties and simple processing. The reported temperature for the fabrication of high-quality CsPbBr3 films is usually higher than 150 °C, which hinders their application in flexible devices. Here, for the first time, high-performance flexible PDs based on CsPbBr3 perovskite films, which showed a broadband spectrum response from blind ultraviolet to visible light, were realized via a modified low-temperature (70 °C) solution-processed method. The perovskite films prepared by this method exhibited improved morphology and high light-harvesting capability. The device also yielded high ON/OFF ratio (103), fast response speed (260 ms, rise time) and high responsivity (0.24 mA W-1) for solar-blind UV light (254 nm) at 2 V. Moreover, the photodetector exhibited outstanding mechanical flexibility and long-term environmental stability for two months without encapsulation. Our work paves the way for the realization of cost-efficient high-performance flexible optoelectronic devices.

Perovskite Solar Cells with ZnO Electron-Transporting Materials.

Perovskite solar cells (PSCs) have developed rapidly over the past few years, and the power conversion efficiency of PSCs has exceeded 20%. Such high performance can be attributed to the unique properties of perovskite materials, such as high absorption over the visible range and long diffusion length. Due to the different diffusion lengths of holes and electrons, electron transporting materials (ETMs) used in PSCs play a critical role in PSCs performance. As an alternative to TiO2 ETM, ZnO materials have similar physical properties to TiO2 but with much higher electron mobility. In addition, there are many simple and facile methods to fabricate ZnO nanomaterials with low cost and energy consumption. This review focuses on recent developments in the use of ZnO ETM for PSCs. The fabrication methods of ZnO materials are briefly introduced. The influence of different ZnO ETMs on performance of PSCs is then reviewed. The limitations of ZnO ETM-based PSCs and some solutions to these challenges are also discussed. The review provides a systematic and comprehensive understanding of the influence of different ZnO ETMs on PSCs performance and potentially motivates further development of PSCs by extending the knowledge of ZnO-based PSCs to TiO2 -based PSCs.

Solvent annealing of PbI2 for the high-quality crystallization of perovskite films for solar cells with efficiencies exceeding 18.

While most work carried out to date has focused on the solvent annealing of perovskite, in the present work, we focused on the solvent annealing of lead iodide. Based on the two-step spin-coating method, we designed a screening method to search for an effective solvent annealing process for PbI2. PbI2 films were annealed in diverse solvent atmospheres, including DMF, DMSO, acetone, and isopropanol (IPA). We found that the solvent annealing of PbI2 in the DMF, acetone, and IPA atmospheres resulted in dense PbI2 films, which impeded the complete conversion of PbI2 to CH3NH3PbI3. Surprisingly, employing the DMSO solvent annealing process for PbI2 led to porous PbI2, which facilitated the complete conversion of PbI2 to perovskite with larger grain sizes. Solar cells fabricated using the DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%. This unique solvent annealing method presents a new way of controlling the perovskite film quality for highly efficient solar cells.