Optimising Non-Patterned MoO3/Ag/MoO3 Anode for High-Performance Semi-Transparent Organic Solar Cells towards Window Applications.

Semi-transparent organic solar cells (ST-OSCs) have attracted significant research attention, as they have strong potential to be applied in automobiles and buildings. For ST-OSCs, the transparent top electrode is an indispensable component, where the dielectric/metal/dielectric (D/M/D) structured electrode displayed a promising future due to its simplicity in the fabrication. In this work, by using the MoO3-/Ag-/MoO3-based D/M/D transparent electrode, we fabricated ST-OSCs based on the PM6:N3 active layer for the first time. In the device fabrication, the D/M/D transparent electrode was optimised by varying the thickness of the outer MoO3 layer. As a result, we found that increasing the thickness of the outer MoO3 layer can increase the average visible transmittance (AVT) but decrease the power conversion efficiency (PCE) of the device. The outer MoO3 layer with a 10 nm thickness was found as the optimum case, where its corresponding device showed the PCE of 9.18% with a high AVT of 28.94%. Moreover, the colour perception of fabricated ST-OSCs was investigated. All semi-transparent devices exhibited a neutral colour perception with a high colour rendering index (CRI) over 90, showing great potential for the window application.

Burn-In Degradation Mechanism Identified for Small Molecular Acceptor-Based High-Efficiency Nonfullerene Organic Solar Cells.

Organic solar cells (OSCs) have again become a hot research topic in recent years. The record power conversion efficiency (PCE) of OSCs has boosted to over 17% in 2020. Apart from the high PCE, the stability of OSCs is also critical for their future applications and commercialization. Recently, many studies have proposed that burn-in degradation can be considered as an ineluctable barrier to long-term stable OSCs. However, there is still lack of studies to explain the detailed mechanism of this burn-in process. In this work, we first investigated the mechanism of the burn-in process in the high-efficiency PM6:N3-based nonfullerene OSCs. The PM6:N3-based device achieved a profound average PCE of 14.10% but also showed a significant performance loss after the burn-in degradation. Following characterizations such as dark J-V, photoluminescence (PL), time-resolved PL, Urbach energy estimation, and electrochemical impedance spectroscopy reveal that the burn-in degradation observed is closely related to the current extraction, energy transfer, nonradiative recombination, and charge transport process in the PM6:N3-based device. At the same time, it has small effects on the exciton dissociation process and energetic disorder in the PM6:N3-based device. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and grazing incidence X-ray diffraction measurements gratifyingly found that the morphology of the PM6:N3 active layer is relatively stable during the burn-in degradation. Therefore, these observed degradations are suspected results from the instability of interfaces and electrodes. The atoms in carrier transport layers and electrodes may diffuse to the active layer during the degradation, which changes the energy levels of each layer and causes traps at the interface and in the active layer. Conquering the instability of interfaces and electrodes is proposed as the prior task for PM6:N3-based OSCs to achieve long-term stability. Our study provides insights into the mechanism behind the burn-in degradation of the PM6:N3-based OSCs, which takes the first step to conquer this barrier.

Effects of Hydroiodic Acid Concentration on the Properties of CsPbI3 Perovskite Solar Cells.

Inorganic cesium lead triiodide (CsPbI3) perovskite materials are becoming increasingly attractive for use in perovskite/silicon tandem solar cells, due to their almost ideal band gap energy (E g) of about 1.7 eV. To be useful as photovoltaic absorbers, the CsPbI3 must form the cubic or black phase (α-CsPbI3). To do so at relatively low temperatures, hydroiodic acid (HI) is required as a solution additive. This paper demonstrates CsPbI3 perovskite solar cells with an efficiency of 6.44%, formed using a HI concentration of 36 µL/mL. This value is higher than the previous most commonly used HI additive concentration. Herein, by undertaking a systematic study of the HI concentration, we demonstrate that the structural, morphological, optical, and electrical properties of CsPbI3 solar cells, processed with this HI additive concentration, are superior.