Organic perovskites are promising semiconductor materials for advanced photoelectric applications. Their fluorescence typically shows a negative temperature coefficient due to bandgap change and structural instability. In this study, a novel perovskite-based composite with positive sensitivity to temperature was designed and obtained based on its inverse temperature crystallization, demonstrating good flexibility and solution processability. The supercritical drying method was used to address the limitations of annealing drying in preparing high-performance perovskite. Optimizing the precursor composition proved to be an effective approach for achieving high fluorescence and structural integrity in the perovskite material. This perovskite-based composite exhibited a positive temperature sensitivity of 28.563% ℃⁻¹ for intensity change and excellent temperature cycling reversibility in the range of 25–40 ℃ in an ambient environment. This made it suitable for use as a smart window with rapid response. Furthermore, the perovskite composite was found to offer temperature-sensing photoluminescence and flexible processability due to its components of perovskite-based compounds and polyethylene oxide. The organic precursor solvent could be a promising candidate for use as ink to print or write on various substrates for optoelectronic devices responding to temperature.

Perovskite solar cells (PSCs) have been demonstrated to be one of the most promising technologies in the field of renewable energy. However, the presence of the defects in the perovskite films greatly limits the efficiency and the stability of the PSCs. The additive engineering is one of the most effective approaches to overcome this problem. Most of the successful additives are extracted from the petroleum-based materials, while the research on the biomass-based additives is still lagging behind. In this paper, two ecofriendly hydroxyalkyl cellulose additives, i.e., hydroxyethyl cellulose (HEC) and hydroxylpropyl cellulose (HPC), are investigated on the performance of the MAPbI₃-based inverted PSCs. Due to the strong interaction between the hydroxyl groups of the cellulose and the divalent cations of the perovskite, these additives enhance the crystal grain orientation and significantly repair the defects of the perovskite films. Working as the additives, these two cellulose derivatives show a strong passivation ability, which significantly reduces the trap density and improves the optoelectronic feature of the PSCs. Compared with the average power conversion efficiency (PCE) of the control device (19.19%), an enhancement of ~10% is achieved after the addition of HEC. The optimized device (PCE = 21.25%) with a long-term stability (10:80 h, PCE = 20.93%) is achieved by the incorporation of the HEC additives into the precursor solution. It is the best performance among the PSCs with the cellulose additives up to now. This research provides a novel choice to develop a cost-effective and renewable additive for the PSCs with high efficiency and excellent long-term stability.

Although metal halide perovskites are increasingly popular for the next generation of efficient photovoltaic devices, the inevitable defects from the preparation process have become the notorious barrier to further improvement of performance, which increases non-radiative recombination and lowers the power conversion efficiency of solar cells. Surface passivation strategies have been affirmed as one of the most practical approaches to suppress these defects. Therefore, it is necessary to have a detailed review on the surface passivation to reveal the improvements of the devices. Herein, the mechanism and recent advances of surface passivation have been systematically summarized with respect to various passivation approaches, including the Lewis acid–base, the low-dimensional perovskite, inorganic molecules, and polymers. Finally, the review also offers the research trend and prospects of surface passivation.

Lead-free double perovskite Cs₂AgBiBr₆ has gained increasing attention recently. However, the power conversion efficiency (PCE) of Cs₂AgBiBr₆ perovskite solar cells (PSCs) is still low compared with their lead-based counterparts. Here, by using photoluminescence (PL), time-resolved photoluminescence (TRPL), and ultrafast transient absorption (TA) measurements, the unbalance between the electron and hole in diffusion and transfer, which limits the performance of the Cs₂AgBiBr₆ PSCs, was further revealed. Considering this issue, a strategy of using the mesoporous TiO₂ electron transport layer (ETL) to construct a bulk heterojunction in Cs₂AgBiBr₆ PSCs was proposed. Consequently, the PCE had improved by over 24% comparing with that only used compact TiO₂ ETL. Moreover, based on mesoporous TiO₂, the unencapsulated Cs₂AgBiBr₆ PSCs maintained 90% of their initial performance after approximately 1200 h of storage in a desiccator (humidity ~30%). This work gives further understanding of Cs₂AgBiBr₆ perovskite and demonstrates that a proper design of balancing the electron and hole diffusion can improve device performance.

All-inorganic metal-halide CsPbBr₃ perovskite has emerged as an attractive photovoltaic material for its outstanding environmental stability. However, due to the wide bandgap, the performance of CsPbBr₃ perovskite solar cells (PSCs) is limited, especially for the short-circuit current density (J_SC). In this issue of Energy & Environmental Materials, Guo et al. employed Nb-doped SnO₂ as electron transporting layers (ETLs), which could greatly improve the J_SC of the PSCs based on all-inorganic CsPbBr₃.