Highly Efficient Flexible Photodetectors Based on Pb-Free CsBi3I10 Perovskites.

Perovskites have made remarkable advancements in optoelectronics owing to their high light absorption coefficient, tunable bandgap, and long charge diffusion. Nonetheless, the practical applications of Pb-based perovskites have been hindered by the instability and toxicity of Pb, especially in flexible electronics, which require high biosecurity and low toxicity. Hence, the development of stable Pb-free perovskite materials has gained increasing attention. In this study, we synthesized stable CsBi3I10 Pb-free perovskites outside the glovebox and improved the optoelectronic and mechanical performances of the CsBi3I10-based flexible devices through polyvinylcarbazole (PVK) doping. Flexible photodetectors with the device structure of PET/ITO/PEDOT:PSS/CsBi3I10:PVK/Au was fabricated. The results indicated that the introduction of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) reduced the surface roughness of the flexible PET substrate, while PVK doping further improved the surface smoothness of CsBi3I10 thin films, thereby enhancing the interfacial charge transportation. Moreover, PEDOT:PSS and PVK acted as stepwise hole transport layers in the photodetectors. The device demonstrated a maximum responsivity of 0.3 A/W, detectivity of 2.6 × 1011 Jones, and a response time of 102 µs at 650 nm. After subjecting it to 1000 bending tests, the light current retained 80% of its initial value. This study presents a universally applicable method for controlling the surface morphology of a flexible perovskite thin film.

Ultrahigh-Q lithium niobate microring resonator with multimode waveguide.

Difficulty in etching lithium niobate (LN) results in a relatively high propagation loss, which necessitates sophisticated processes to fabricate high-quality factor (Q) microresonators. Here, we fabricate a multimode microring resonator with an intrinsic Q of 6 × 106, which exhibits a propagation loss 50 times lower than that of a single-mode LN microring fabricated under the same process. Notably, the excitation of higher-order modes in the multimode microring is effectively suppressed by utilizing the Euler bend. The highly regular transmission spectrum of the resonator demonstrates a free spectral range (FSR) of 56 GHz. Based on this microresonator, we implement a bandpass microwave photonic filter with an ultra-narrow 3 dB bandwidth of 47.5 MHz and a large tuning range of 2-26.5 GHz. It can be anticipated that the combination of existing advanced etching techniques with this work will drive the propagation loss of a LN waveguide closer to the material absorption loss, significantly facilitating the optimization of performance in applications requiring ultrahigh-Q LN microresonators, such as frequency combs, frequency conversion, electro-optic modulation, and quantum photonics.