Interface engineering is very important to the high performance of organic optoelectronic devices that are commonly composed of multilayer thin solid films. Interfacial materials are particularly crucial for interface engineering, and a variety of materials have been employed at the interface to accomplish various different functions. This Review summarizes various materials for the interfaces and some of the latest progress in organic solar cells (OSCs) and organic photodetectors (OPDs).

Aqueous zinc hybrid batteries have been rapidly developed to overcome the sluggish kinetics of divalent zinc ions in the cathode of Zn-based batteries. However, their cycle life is limited by water decomposition during the operation, specifically at low current rate for long-term cycles. Herein, we propose a zinc hybrid battery with excellent adaptability of lowtemperature, at which the water decomposition is seriously restrained. The battery involves a hygroscopic double-layer gel polymer electrolyte, in which one layer close to the LiFePO 4 cathode provides Li + , and the other layer close to the Zn anode provides Zn 2 + . The use of the double-layer electrolyte can both weaken the water reactivity and increase the salt concentration, leading to a high-performance of the batteries. It enables the hybrid batteries to operate at À 20°C and achieve stability for over 300 cycles with a capacity retention of 85.14 % and Coulombic efficiency of~100 % at a low current rate of 85 mA g À 1 . Moreover, the spontaneous hygroscopic system, opposite to that of "water-in-salt", can efficiently reduce manufacturing costs and improve ionic conductivity. This provides an advanced pathway for designing electrolytes to achieve high-performance and low-cost batteries with excellent adaptability of low-temperature.

Aqueous copper metal batteries with acidic electrolytes are regarded as promising candidates for low-temperature energy storage, benefiting from fast kinetics of protons and acid resistance of copper. Here, a Cu(BF 4 ) 2 electrolyte that spontaneously generates protons is developed for ultralow-temperature copper metal batteries. Systematic studies demonstrate that the hydrolysis of BF 4 À generates more protons, rendering the Cu(BF 4 ) 2 among the most effective aqueous electrolyte capable of breaking hydrogen bonds in water molecules. This electrolyte endows a polyaniline/Cu battery to deliver a short charging time of 21 s and a charge/discharge capability of up to 10 A g À 1 at À 30 °C, along with a high discharge specific capacity of 70 mAh g À 1 and a supercapacitor-comparable power density of 3000 W kg À 1 . Furthermore, it can exhibit a long and stable cycling lifespan over 10 000 cycles at À 50 °C and works well at À 70 °C. This work provides an opportunity for intrinsically acidic electrolytes.

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Aqueous copper metal batteries with acidic electrolytes are regarded as promising candidates for low-temperature energy storage, benefiting from fast kinetics of protons and acid resistance of copper. Here, a Cu(BF 4 ) 2 electrolyte that spontaneously generates protons is developed for ultralow-temperature copper metal batteries. Systematic studies demonstrate that the hydrolysis of BF 4 À generates more protons, rendering the Cu(BF 4 ) 2 among the most effective aqueous electrolyte capable of breaking hydrogen bonds in water molecules. This electrolyte endows a polyaniline/Cu battery to deliver a short charging time of 21 s and a charge/discharge capability of up to 10 A g À 1 at À 30 °C, along with a high discharge specific capacity of 70 mAh g À 1 and a supercapacitor-comparable power density of 3000 W kg À 1 . Furthermore, it can exhibit a long and stable cycling lifespan over 10 000 cycles at À 50 °C and works well at À 70 °C. This work provides an opportunity for intrinsically acidic electrolytes.