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Metal halide perovskite ferroelectrics possess various physical characteristics such as piezoelectric and pyroelectric effects, which could broaden the application of perovskite ferroelectrics and enhance the optoelectronic performance. Therefore, it is promising to combine multiple effects to optimize the performance of the self-powered PDs. Herein, patterned 2D ferroelectric perovskite (PMA)sub2/subPbClsub4/submicrobelt arrays were demonstrated through a PDMS template-assisted antisolvent crystallization method. The perovskite arrays based flexible photodetectors exhibited fine self-powered photodetection performance under 320 nm illumination and much enhanced reproducibility compared with the randomly distributed single-crystal microbelts-based PDs. Furthermore, by introducing the piezo-phototronic effect, the performance of the flexible PD was greatly enhanced. Under an external tensile strain of 0.71%, the responsivity was enhanced by 185% from 84 to 155.5 mA/W. Our findings offer the advancement of comprehensively utilizing various physical characteristics of the ferroelectrics for novel ferroelectric optoelectronics.

The Si-QDs/SiO2 multilayer films with phosphorus (P) doping have been prepared, and carrier multiplication effect of the films with and without P doping was investigated by relative quantum yield of photoluminescence (PL). The relative quantum yield of PL shows a step like increase when the excitation energy is larger than 2 E g of Si-QDs, and the carrier multiplication is caused by space-separated quantum cutting in adjacent QDs. The PL peak shifts toward high energy region after P-doping, and the PL intensity is enhanced, however, the threshold energy for carrier multiplication is decreased from 2.97 to 2.89 eV. The results suggest that non-radiative recombination at the surface of Si-QDs is suppressed by P passivation, and radiative recombination from conduction band to surface defect level is possible. Energy transfer from hot electron-hole pair to surface defect level leads to the optical excitation of defect level, which generates an extra electron-hole pair, and carrier multiplication effect is observed in the P-doped multilayer film with lower excitation energy.

CsPbI3 nanocrystals (NCs) with photoluminescence quantum yield (PLQY) larger than 90% have been synthesized at different temperature regions, and the physical origins for high PLQY were investigated. HRTEM images show that cubic phase CsPbI3 (α-CsPbI3) is surrounded by hexagonal Cs4PbI6 in the low temperature region, and the ratio of CsPbI3 and Cs4PbI6 increases with increasing the reaction temperature. The strong confinement effect of Cs4PbI6 leads to the high PLQY (95%) of α-CsPbI3 NCs when the reaction temperature is 120 °C. The confinement effect of Cs4PbI6 is weakened with increasing reaction temperature, which leads to the decrease of PLQY at 140 °C. However, non-radiative recombination is suppressed due to the microstructure improvement with further increasing the reaction temperature, and PLQY as high as 97% is achieved at 180 °C. Stability testing shows that fast degradation of α-CsPbI3 NCs occur in low reaction temperature region, and α-CsPbI3 NCs with high PLQY can be stored in air for 90 days when the reaction temperature is 180 °C.

Phosphorus (P) doped Si-quantum-dots/SiO 2 multilayer films have been deposited by plasma enhanced chemical vapor deposition (PECVD) technique, and Si quantum dots (Si-QDs) are obtained by the following annealing treatment. Raman and transmission electron microscopy (TEM) results show that P doping prevents the growth of Si-QDs. The photoluminescence (PL) intensity can be enhanced by proper P doping, and a maximal PL intensity is obtained when the doping flow ratio of phosphine and silicane is 0.75%. The resistivity of the films is reduced by P doping, and proper doping leads two orders of magnitude lower than that of the intrinsic films. Analysis shows that proper P doping in the multilayer films could fill the carrier capture center in interface and suppress the non-radiative recombination of carriers.

Si quantum dots (Si-QDs)/SiO2 multilayer films have been fabricated on Si substrate, and the carrier transport properties of heterojunctions consisting of Al:Si/SiO2:Si:Al are studied. The current density–voltage curves show that high density Si-QDs lead to higher current density and rectifying ratio. The carrier transports in the forward voltage are controlled by Ohmic resistance model, tunneling and recombination limited current (TRLC) model, and space-charge limited current (SCLC) model, respectively. The TRLC is quenched by hydrogen passivation, while the SCLC-limited carrier transport process becomes the main carrier transport mechanism, and a 7.6 times current density enhancement is obtained. It suggests that the SCLC-limited model is more effective for carrier transport in the studied device.

Si quantum dots (Si-QDs) embedded in SiO 2 films have been prepared and multiple photoluminescence (PL) bands are obtained when the annealing temperature is below 900 °C. Microstructure analyses show that the Si-QDs are crystallized only when the annealing temperature is as high as 1000 °C, and the ultra-small Si-QDs are surrounded by SiO x compounds. Multiple peaks can be observed in the PL and PL excitation spectra. The multiple PL bands can be fitted to a broad band located at 2.2 eV together with seven narrow bands, and the energy separations for the adjacent narrow PL bands are between 140 meV and 158 meV, while the PL excitation spectrum can be fitted to eight optical excitation bands with energy separations about 160 meV. The broad PL band located at 2.2 eV is related to self-trapped exciton optical emission of ultra-small Si-QDs, while the narrow bands are caused by optical phonon assisted optical emissions, and both the PL excitation and emission processes can be explained in the configurational–coordinate model. Time-resolved PL spectra show that the average decay times of 8.9–9.5 ns are obtained for all the narrow PL peaks.

In this work, Si-rich oxide (SRO)/SiO2 multilayer films have been deposited and the photoluminescence (PL) decay properties of the films with different annealing temperatures are studied. The PL shifts toward low energy with increasing the annealing temperature, and intense PL at around 1.4 eV is obtained after annealing at 1100 °C. The PL decay curves can be well fitted by a multiexponential PL decay model, and the peak of the PL lifetime distribution band shifts toward longer time with increasing the annealing temperature. Two lifetime distribution bands are obtained after the formation of crystallized Si-QDs, and the proportion of slow component increases from 69.72% to 77.04% after hydrogen passivation. Analyses show that defect states recombination in the SRO layer is the main optical emission mechanism when the annealing temperature is lower than 900 °C, and interband transition in the Si-QDs due to quantum confinement effect is the main PL mechanism when the film is annealing at 1100 °C.

The carrier recombination processes in low density nanocrystalline (nc-) Si films have been studied by steady and time-resolved photoluminescence (PL) spectra, and the hot carriers have been excited to a high energy state by impact excitation. A yellow-green PL band locating at 580 nm appears when the studied film is excited by two optical beams. The yellow-green PL band results from band-to-band transition in Si nanocrystals with double-bonded oxygen atoms, which is caused by impact excitation among the carriers in the nc-Si film. The decay time of the yellow-green PL band is 230 ns, which is much longer than the hot carrier cooling. The results indicate that the lost energy in the solar cell may be collected from the new recombination center in the further structural design.

A report on strong and fast blue photoluminescence (PL) from silicon nanocrystals (Si-ncs) suspended in toluene solution is presented. They were fabricated through nanosecond pulsed laser ablation of the silicon target in toluene. Transmission electron microscopy observations confirm that the Si-ncs are well dispersed and the most of them are smaller than 2 nm. Fourier transform infrared spectra indicate that the surface of the Si-ncs is passivated by some groups from toluene. The detailed study of PL spectra and PL excitation spectra reveals that the photoexcited carriers not only are present in the quantum confined Si-ncs cores but also occur at the Si-ncs surface, and the resonant electron transfer from the surface bonding states to the conduction band of quantum confined Si-ncs can efficiently occur. Time-resolved PL spectrum exhibits a triple-exponential PL decay with lifetimes of 0.73, 3.8 and 13.5 ns, and implies that the optical recombinations and the resonant electron transfer are both very rapid and of the order of nanoseconds.

Nanocrystalline (nc)-SiC film has been deposited by helicon wave plasma enhanced chemical vapor deposition technique and intense blue-white light emission is obtained. Microstructure analyses show that the 3C–SiC particles are embed in amorphous SiC matrix, and the average size of the nc-SiC is 3.96 nm. The photon energy of the main photoluminescence (PL) band is higher than the band gap of bulk SiC, which indicates that the optical emission mainly occurs in quantum states of 3C–SiC nanocrystals. In addition, the band tail states of amorphous SiC also contribute to the optical emission. Three decay processes are obtained from time-resolved PL spectra by deconvolution treatment, and the decay components correspond to the quantum confinement effect (QCE), surface states of nc-SiC particles, and band tail of amorphous SiC, respectively. The fractional integrated PL intensity of QCE related decay process decreases dramatically in the lower PL photon energy, indicating that the QCE mainly contributes to the short wavelength optical emission.

Hydrogenated nanoamorphous Si (na-Si:H) films have been fabricated by reactive pulsed laser ablation technique with hydrogen as reactive gas. It is found that the hydrogen pressure has a great effect on both the structure and photoluminescence (PL) properties of the films. Increasing the hydrogen pressure leads to a structural transition of the films from amphorous Si to na-Si:H, and the PL center wavelength of the na-Si:H films is varied with the hydrogen pressure. The PL decay times of the na-Si:H films are in the nanosecond scale and are shorter on the high energy side of their PL spectrum. The results demonstrate that the na-Si:H films are promising candidates for visible, tunable and high-performance light-emitting devices.

Nanocrystalline silicon carbide (nc-SiC) thin films have been grown on silicon (1 0 0) substrates by helicon wave plasma enhanced chemical vapor deposition technique and the photoluminescence of the films has been tuned from yellow to blue by changing the substrate temperatures (Ts). The resulting nc-SiC films show a microstructure of 3C–SiC nanocrystallites embedded in hydrogenated amorphous SiC matrix. Detailed analysis of the infrared absorption reveals that the degree of crystallization of the films increases with the increase of Ts while the content of hydrogen-related bonds in the films is decreased. The photoluminescence spectra of the nc-SiC films are found to be composed of two Gaussian components. As the Ts increases, the component with higher energy shows a growing trend and the corresponding peaks move to high energy side, indicating that the main luminescence mechanism in the films changes from the defect-related carrier recombination to the quantum confinement effect.

Si-rich oxide/SiO 2 multilayer films with different N 2 O flow rates have been deposited by plasma enhanced chemical vapor deposition technique, and Si quantum dot (Si-QD)/SiO 2 multilayer films are obtained by 1100 °C annealing. Steady photoluminescence (PL) spectra show that the main optical emission mechanism changes from quantum confinement effect of Si-QDs to interface defect states with increasing the flow rate of N 2 O. Curve fittings of time-resolved PL spectra show that two log-normal decay time distribution bands are obtained, and both the most frequent life-times decrease with increasing the flow rate of N 2 O, while increase with the red shift of detecting wavelength. Analyses indicate that defect states density and size distribution of Si-QDs strongly influence the PL decay properties.

Nanocrystalline silicon embedded in silicon oxide (nc- Si/SiO2 ) films have been in situ grown at a low substrate temperature of 300°C by reactive magnetron co-sputtering of Si and SiO2 targets in a mixed Ar/H2 discharge. The influences of H2 flow rate (F H ) on the microstructural properties of the deposited nc- Si/SiO2 films were investigated. The results of XRD and the deposition rate of nc- Si/SiO2 films show that the introduction of H2 contributes to the growth of nc- Si grains in silicon oxide matrix. With further increasing F H , the average size of nc- Si grains increases and the deposition rate of nc- Si/SiO2 films decreases gradually. Fourier transform infrared spectra analyses reveal that introduction of hydrogen contributes to the phase separation of nc- Si and SiO x in the deposited films. Moreover, the Si–O 4-n Si n(n = 0, 1) concentration of the deposited nc- Si/SiO2 films reduces with the increase of F H , while that of Si – O 4-n Si n(n = 2, 3) concentration increases. These results can be explained by that active hydrogen atoms increase the probability of reducing oxygen from precursor in the plasma and prompting oxygen desorption from the growing surface. This low-temperature procedure for preparing nc- Si/SiO2 films opens up the possibility of fabricating the silicon-based thin-film solar cells onto low-cost glass substrates using nc- Si/SiO2 films.