Study On Preparation And Photoelectric Properties Of Sb₂Se₃ Heterostructure

In order to solve the energy crisis and environmental pollution,people pay more and more attention to the power generation by photovoltaic.Nowadays silicon-based solar cells account for over 90%of the solar-cell market.But due to the high price of silicon and high cost of synthesis process,it has a great problem for the further development of photovoltaic power generation.Therefore,the exploration of low-cost,high-efficient solar cells is a primary task for the future of photovoltaic generation.The maximum distance between photogenerated carriers and junction regions in nanostructured solar cells with bulk heterojunction networks depends on the size of the materials.It means that it depends on the micro-structure of the materials.The thickness of light absorption layers of nanostructured solar cells ranges from tens to hundreds of nanometers.This specific structure can reduce the requirement of diffusion length of the absorption materials so that some cheap materials with poor electrical properties but strong light absorption can be utilized.Antimony selenide?Sb₂Se₃?has suitable bandgap and extremely high visible-NIR absorption coefficient.It indicates that Sb₂Se₃ has great potential to be the light absorbing layer of solar cells.However,Sb₂Se₃ has a low carrier mobility which hinder its application in solar cells.Constructing bulk heterojunction network is a way to solve this problem.In this paper,Sb₂Se₃ used as a light-absorbing material and another material,Cu₂GeSe₃,with high conductivity as a carrier transport material,form an heterojunction network.The separation and migration of photoinduced carriers are improved due to the specific microstructure,and the recombination probability of electron-hole pairs is reduced as well.Furthermore,reasonable device structures are designed,and a novel solar cell as well as the fabrication techniques is obtained.The paper can be divided in three sections,as follows:?1?The morphology and photo-electrical properties of Sb-Ge-Se-CuI chalcogenide glass-ceramics with different composition have been studied.The materials were characterized by SEM,EDS and XRD.The photoelectric properties were characterized by PEC and 4-probe measuring sheet resistivity.The kinetic parameters such as crystallization activation energy and kinetic factor are calculated by Ozawa and Kissinger crystallization models and the formation mechanism of bulk heterojunction structure during heat treatment process is analyzed.The study shows that the internal network heterojunction can be formed in the 40Ge Se₂-20Sb₂Se₃-20CuI chalcogenide glass after proper heat treatment.The structure can improve the conductivity and the carrier separation and migration rate.According to the calculation by Ozawa and Kissinger's method,the activation energy of crystallization of 40GeSe₂-20Sb₂Se₃-20CuI turns out to be 190 KJ/mol and the kinetic parameter is 1.1.It indicates that the crystallization process is mainly governed by one-dimension growth.The co-crystallization behavior of the 40GeSe₂-20Sb₂Se₃-20CuI chalcogenide is the key to form the internal heterojunction network.?2?The deposition of 40GeSe₂-20Sb₂Se₃-20CuI amorphous thin film and its controllable crystallization is mainly discussed.The thin films were characterized by SEM,EDS and XRD.The photoelectric properties were characterized by PEC and 4-probe measuring sheet resistivity.Two ways of thin film deposition,i.e.,magnetron RF sputtering and pulse laser deposition,are compared with each other to find a best way for preparing Sb-Ge-Se-CuI chalcogenide glass thin films.The effects of heat treatment parameters and film composition on the structure of the bulk heterostructure are analyzed.The study shows that 1.the films prepared by magnetron sputtering have a small amount of O element in the film,and the film composition deviates from the target composition.With heat treatment at 280?,a complete heterojunction network structure can be evidently observed in the thin film.It is found that the Sb₂Se₃/Cu₂GeSe₃ internal heterojunction network endows the films with excellent photoelectric properties and high conductivity,which are confirmed by photoelectrochemical measurement and four-probe resistance measuring.2.By using pulse laser deposition to prepare the films,the composition of the thin film and the target is almost the same.The oxygen content is too low to be detected.When heat-treatedat 260?,a complete heterojunction network structure can be evidently observed in the thin film.It also shows a great performance at conductivity and photoelectric properties.3.Comparing the two preparation processes,it is found that the film prepared by magnetron sputtering has a stronger photocurrent response than those prepared by pulse laser deposition.However,due to the fact that thin film prepared by PLD doesn't show any evaporation during the heat treatment,the film is denser.It is shown that PLD process is more proper for the preparation of solar-cell light-absorption layer.?3?The fabrication of thin film solar cells with Sb₂Se₃/Cu₂GeSe₃ heterojunction network as the light absorbing layer is studied.The heterojunction network is prepared by RF magnetron sputtering or pulsed laser deposition,combined with appropriate heat treatment crystallization process.Nanostructured solar cells with FTO/TiO₂/Sb₂Se₃-Cu₂GeSe₃/Spiro-OMeTAD/Ag structure are prepared.We find that the devices obtained by pulsed laser deposition are superior to those prepared by RF magnetron sputtering.The former devices with the value of 0.2 V,1.37mA/cm² and 38%for V_oc,J_sc and fill factor,respectively,yielding a PCE of 0.27%.This work suggests the Sb₂Se₃/Cu₂GeSe₃ heterojunction network fabricated by controllable crystallization is promising to be used as the absorption layer for solar cells.