Analysis of the UV ozone-treated SnO2 electron transporting layer in planar perovskite solar cells for high performance and reduced hysteresis

Tin oxide (SnO2) is widely used as electron transporting layer (ETL) in perovskite solar cells (PSCs) because its good transparency, band alignment to perovskite and stability. The interface between the ETL and the perovskite in the PSCs affects the charge extraction process and may influence the optoelectronic properties. Surface treatment of SnO2, such as the UV-ozone (UVO) treatment has been shown to enhance the efficiency and reduce the light soaking effect of the PSCs. Herein, we report the success in control and suppressing hysteresis reaching as highest photoconversion efficiency 19.4% with negligible hysteresis for the devices growth on 60 minutes UVO treated SnO2. The wettability of treated SnO2 is well-matched with the polar solvent of the perovskite solution, leading to complete coverage of the substrate, although the treatment does not affect the morphology and the crystallinity of the perovskite thin films. Impedance spectroscopy measurements analysis, clearly indicate the decrease of recombination rate after UVO treatment and the reduction of low frequency capacitance causing a reduction of current-potential curve hysteresis

Optimizing Performance and Operational Stability of CsPbI3 Quantum-Dot-Based Light-Emitting Diodes by Interface Engineering

Perovskite light-emitting diodes (PeLEDs) have emerged as a promising candidate for next-generation display technology and lighting applications owing to their high current efficiency, low operating voltage, narrow spectral emission, and tunable emission color. Keys to achieving efficient PeLEDs are, besides an emitter layer with high optical quality, a negligible charge injection barrier between charge injecting layers (CILs) and an optimized thickness of these CILs for a controlled flow of charge carriers through the device. In this study, we systematically optimized hole transport layers and electron transport layers (ETLs) in PeLEDs employing CsPbI3 quantum dots as an emitter layer. We also investigated two bilayer cathodes (Liq/Ag and LiF/Al) with the various ETLs employed in our study and observed that 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T) as an ETL improves the band alignment, leading to better electron injection. The improved electron/hole current balance results in ∼63% higher external quantum efficiency (EQE) in PO-T2T-based devices compared to PeLEDs employing other ETLs. In addition, we tracked the operational stability of the different devices observing a correlation with the EQE, where samples with higher EQE (PO-T2T-based devices) also present the highest stable operation at elevated current densities

Boosting Long-Term Stability of Pure Formamidinium Perovskite Solar Cells by Ambient Air Additive Assisted Fabrication

Due to the high industrial interest for perovskite-based photovoltaic devices, there is an urgent need to fabricate them under ambient atmosphere, not limited to low relative humidity (RH) conditions. The formamidinium lead iodide (FAPI) perovskite α-black phase is not stable at room temperature and is challenging to stabilize in an ambient environment. In this work, we show that pure FAPI perovskite solar cells (PSCs) have a dramatic increase of device long-term stability when prepared under ambient air compared to FAPI PSCs made under nitrogen, both fabricated with N-methylpyrrolidone (NMP). The T80 parameter, the time in which the efficiency drops to 80% of the initial value, increases from 21 (in N2) to 112 days (in ambient) to 145 days if PbS quantum dots (QDs) are introduced as additives in air-prepared FAPI PSCs. Furthermore, by adding methylammonium chloride (MACl) the power conversion efficiency (PCE) reaches 19.4% and devices maintain 100% of the original performance for at least 53 days. The presence of Pb–O bonds only in the FAPI films prepared in ambient conditions blocks the propagation of α- to δ-FAPI phase conversion. Thus, these results open the way to a new strategy for the stabilization in ambient air toward perovskite solar cells commercialization.Funding for open access charge: CRUE-Universitat Jaume

Chemi-Structural Stabilization of Formamidinium Lead Iodide Perovskite by Using Embedded Quantum Dots

The approaches to stabilize the perovskite structure of formamidinium lead iodide (FAPI) commonly result in a blue shift of the band gap, which limits the maximum photoconversion efficiency. Here, we report the use of PbS colloidal quantum dots (QDs) as a stabilizing agent, preserving the original low band gap of 1.5 eV. The surface chemistry of PbS plays a pivotal role by developing strong bonds with the black phase but weak ones with the yellow phase. As a result, a stable perovskite FAPI black phase can be formed at temperatures as low as 85 °C in just 10 min, setting a record of concomitantly fast and low-temperature formation for FAPI, with important consequences for industrialization. FAPI thin films obtained through this procedure reach an open-circuit potential (Voc) of 1.105 V, 91% of the maximum theoretical Voc, and preserve the efficiency for more than 700 h. These findings reveal the potential of strategies exploiting the chemi-structural properties of external additives to relax the tolerance factor and optimize the optoelectronic performance of perovskite materials