Star-Shaped Single-Polymer Systems with Simultaneous RGB Emission: Design, Synthesis, Saturated White Electroluminescence, and Amplified Spontaneous Emission

A three-armed star-shaped single-polymer system comprising tris­(4-(3-hexyl-5-(7-(4-hexyl­thiophen-2-yl)­benzo­[<i>c</i>]­[1,2,5]­thiadiazol-4-yl)­thiophen-2-yl)­phenyl)­amine (TN) as red emissive cores, benzo­thiadiazole (BT) as green emissive dopants, and polyfluorene (PF) as blue arms was successfully developed, in which the construction of the star-shaped architectures can depress intermolecular interactions and concentration quenching. The thermal, photophysical, electrochemical, electroluminescent, and amplified spontaneous emission (ASE) properties of the synthesized polymers are systematically investigated. The modulation of the doping concentration of TN and BT can guarantee the partial energy transfer in a star-shaped single-polymer system, further achieving saturated white emission. Consequently, a current efficiency of 2.41 cd A^–1 and Commission Internationale d’Eclairage (CIE) coordinates of (0.34, 0.35) were recorded for TN-R3G4 with 0.03 mol % red core and 0.04 mol % green dopants. The saturated white emission is likely to result from the fine control of partial energy transfer and suppressed intermolecular interactions due to the construction of such a star-shaped single-polymer system. What is more, TN-R3G4 shows impressive ASE characteristics with relatively low threshold of 63 ± 5 μJ/cm², which demonstrates the potential as gain media for organic lasing applications. Our results have provided new insights and better understanding into the photophysical and optoelectronic behaviors of the resulting star-shaped single-polymer systems with simultaneous RGB emission

Water-Free, Conductive Hole Transport Layer for Reproducible Perovskite–Perovskite Tandems with Record Fill Factor

State-of-the-art perovskite–perovskite tandem solar cells incorporate a water-based poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hole transport layer in its low bandgap subcell. However, there is a limitation regarding its use due to the moisture sensitivity of perovskites and the insulating property of PSS. Here, we overcome the limitation by using a water-free and PSS-free PEDOT-based hole transport layer for low bandgap single-junction perovskite solar cells and in perovskite–perovskite tandems. The champion tandem cell produces an efficiency of 21.5% and a fill factor of 85.8%, the highest for any perovskite-based double-junction tandems. Results of photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and conductive atomic force microscopy reveal evidence of enhanced conductivity of water-free and PSS-free PEDOT compared to its conventional counterpart. The use of water-free and PSS-free PEDOT also eliminates decomposition of high bandgap subcell with its interfacing layer stack in a tandem that otherwise occurs with conventional PEDOT:PSS. This leads to enhanced reproducibility of perovskite–perovskite tandems

Efficient Flexible Monolithic Perovskite–CIGS Tandem Solar Cell on Conductive Steel Substrate

Here we report for the first time a monolithic perovskite–CIGS tandem (CIGS = Cu(In,Ga)Se2) solar cell on a flexible conductive steel substrate with an efficiency of 18.1%, the highest for a flexible perovskite–CIGS tandem to date, representing an important step toward flexible perovskite-based tandem photovoltaics