Optoelectronic Devices Based On Silicon Quantum Dots

Silicon quantum dots(Si QDs)have shown the great potential in the application of various fields such as solar cells,light-emitting diodes(LEDs),photodetectors,bioimaging and medical therapy.This is mainly due to not only the excellent properties of optical absorption and emitting,but also the nontoxicity,the abundance of silicon and the compatibility with fabrication technology of bulk silicon.However,the performance of electronic devices based on Si QDs is not excellent.The main reason lies in the lack of research of surface effect and film-forming property.In this work,we synthesize the Si QDs with hydrogen and various kinds of ligands on their surface.The Si QDs act as the active material and layer in optoelectronic devices to absorb and emit the light.To enhance the performance of electronic device based on Si QDs,we research the surface effect and film-forming property and improve the surface and film-forming of Si QDs.The main contexts and innovative results are displayed as follows:(1)We have incorporated Si QDs into the P3HT/PCBM binary system,replacing part of P3HT and PCBM,respectively.The ternary hybrid heterojunction solar cells hav been fabricated and the ratio of Si QDs has been changed to optimize the efficiency of solar cells.When the 5%of PCBM is replaced by Si QDs,the absorption in the range of short wavelength can increase.In addition,the cascade energy-level alignment is able to enhance the transport of photo-generating carriers.The highest efficiency increases from?2.93%to?4.11%can be obtained.It corresponds to a relative increase of?40%with respect to the efficiency of original P3HT/PCBM binary solar cells.(2)The Si QDs,which surface is functionalized with 1-dodecene,are spin coated on the NiO.The all-inorganic infrared quantum dot LED has been fabricated.To improve the performance of the LED,an A1203 interlayer may be deposited by the atomic layer deposition between Si QDs and NiO,which is due to the Al2O3 interlayer may suppress the exciton quenching induced by NiO.It is found that optimum thickness of the A1203 interlayer is?5.7 nm.The thin Al2O3 interlayer cannot suppress the quenching efficiently,but the thick Al2O3 interlayer can introduce the positive charge,resulting in the serious quenching.The incorporation of the A1203 interlayer can also decrease the trap of NiO and leakage in the LED.It is shown that the LED with?5.7 nm Al2O3 interlayer can lead to the highest power density of 14 ?W/cm2,and the increase of the external quantum efficiency by a factor of 10(from?0.01%to 0.1%).In addition,the flexible all-inorganic near-infrared quantum-dot LED can be fabricated by the similar technology.After simple encapsulation,the flexible device can maintain 50%original power density when exposed in the air for?230 h.(3)The high efficient hybrid light-emitting diodes can be fabricated with P3HT.The P3HT acts as the hole transport layer,which is due to the high hole mobility.We have optimized the performance of hybrid LEDs by varying the thickness of P3HT layers.In addition,the PFN can be incorporated between P3HT layer and Si-QD layer to suppress the quenching induced by P3HT and decrease the leakage in the devices.It is found that the incorporation of PFN can lead to the higheat optical power density of 0.49 mW/cm2 and highest EQE values of 3.4%.(4)We demonstrate electroluminescent synaptic devices based on Si QDs with optical outputs.These devices exhibit a series of important synaptic functionalities including paired-pulse facilitation(PPF),transition from short-term plasticity(STP)to long-term plasticity(LTP)and spike-timing-dependent plasticity(STDP).In the meantime,logic functions such as "AND","OR","NAND" and "NOR" are also realized in the intercoupled Si-QD-based electroluminescent synaptic devices.The current results not only help realize the bidirectional conversion between electrical and optical signals in synaptic devices,but also contribute to the development of the in-memory computing capacity of synaptic devices.