Solution-processable Preparation And Photoelectronic Performance Of Semiconductor-sensitized TiO₂ Composite Films

The simple and easy low-temperature solution processing and deposition of inorganic semiconductors are of great interest for large-scale macro electronics applications.Solution processing and deposition of inorganic semiconductors have important implications in the areas of photovoltaics,flat panel displays,thermoelectrics,phase change memory,and thin-film transistors.However,direct solution processing of these bulk materials is typically difficult because of their complete insolubility in“normal”solvents.Toward this goal,it was reported the remarkable ability of alkanethiol-ethylenediamine(en)solvent mixtures to dissolve bulk gray selenium,tellurium,Sn S,and a series of nine V₂VI₃ chalcogenides(where V=As,Sb,Bi and VI=S,Se,Te)at room temperature and ambient pressure.This new alkahest(or“universal”solvent)for chalcogenide semiconductors gives stable inks that upon solution deposition and mild thermal annealing regenerate crystalline chalcogenide thin films.Building off this result,we used a solvent mixture of ethanethiol and ethylenediamine(en)to dissolve chalcogenide semiconductor nanopowder to form a precursor ink that was used to generate semiconductor-sensitized Ti O₂ composite films for photodetectors.This paper takes Sb₂Se₃,Se and SbSI materials using solution-processable to prepare semiconductor-sensitized Ti O₂ composite films as the main research object and carries out the following research work:1.We demonstrate the potential of the TiO₂ thin film(?800 nm in thickness)sensitized with a Sb₂Se₃ layer(?350 nm)grown from solution spin coating and processed by annealing recrystallization at 300°C for high-performance optical detection.From the XRD characterization of the composite film,ITO,Ti O₂,and Sb₂Se₃ and their crystal structures can be identified.The SEM and TEM images are seen that the Sb₂Se₃ layer with a mean thickness of about 350 nm consists of interconnecting nanocrystals is intimately coated on the surface of the Ti O₂ layer.The type-? band alignment,p-Sb₂Se₃/n-Ti O₂ heterojunction,and narrow bandgap of Sb₂Se₃(?1.25 e V)endow the film photodetector with a large photocurrent,high switching stability and on/off ratio(>10³),and fast response speeds(<20 ms)under the broadband visible-near-infrared irradiation in a zero-bias self-powered photovoltaic mode.In particular,the photodetector shows notable resistance to oxidation and moisture for long-term operation,which is linked to the modest surface oxidation(Sb-O)of Sb₂Se₃ and not caused significant changes in the electronic structure,as verified by X-ray photoelectron spectroscopy.2.In this work,high-quality Se thin films are obtained by spin-coating the Se precursor thin films at 180?.The XRD patterns for both anatase Ti O₂ and hexagonal phase of Se are retained in the composite Se/Ti O₂ sample,verifying the successful introduction of Se into Ti O₂ composite film.The SEM images show that the Se films are ca.1 um thick with a crystalline morphology.By selecting Se and Ti O₂ as a photosensitizer layer and an electron transport layer,a Se thin-film photodevice with a structure of ITO/Se/Ti O₂/ITO is fabricated,yielding a large photocurrent,high switching stability and on/off ratio(1124),and fast response speeds(?_r?17.61ms/?_d?10.51 ms)under the broadband visible-near-infrared irradiation in a zero-bias self-powered photovoltaic mode.The un-encapsulated device shows a good oxidation-resistant characteristic and air stability.The 64.2%of the photocurrent is still maintained after 72 h of water immersion,and the performance decreases by only10.8%after 2 months of storage in the ambient environment(oxygen and humidity)at room temperature.3.Ternary SbSI layer is prepared by solution processing,followed by preparing the SbSI precursor thin films on a mesoporous Ti O₂ electrode,annealing under a nitrogen atmosphere at a low temperature(180°C)without any external pressure.We have successfully prepared SbSI-sensitized Ti O₂ composite film,and characterized it in detail using TGA/DSC,SEM,XRD,Raman,UV-vis,XPS,and current-voltage measurement.On the basis of TGA/DSC data,SbSI decomposes to Sb₂S₃ residue at around 257.6?.These films were used to construct photodetectors in a sandwich-type architecture.The devices achieved high switching stability and on/off ratio(1100)under simulated sunlight(white light,100 m W/cm²)in a zero-bias self-powered photovoltaic mode.In time response measurements,raise and fall times of less than 18.51 ms and 44.08 ms were determined.The solution-processed SbSI thin films greatly simplifies the production efficiency of SbSI photodetectors.