The Study Of The Doping Of Antimony Selenide Thin Films And Its Effects On Photovoltaic Device Performance

Antimony selenide（Sb₂Se₃）is a promising absorber material for photovoltaic applications due to its suitable fundamental band gap（¹.03 eV）,high absorption coefficient（>105 cm-1）,excellent electronic properties,non-toxicity,low cost,earth-abundant constituents,and intrinsically benign grain boundaries,if suitably oriented.Using a simple and fast（～1 μm min–1）rapid thermal evaporation process（RTE）,our group oriented crystal growth perpendicular to the substrate,and produced Sb₂Se₃ thin-film solar cells with a certified device efficiency of 5.6% in 2015.In order to fabricate the non-toxic solar cell,recently,we replace ZnO to CdS as the N-type buffer in the superstrate configuration and again obtained a 5.93% certified efficiency with excellent stability.Encouraged by our work,searver research groups also joined us and carried out the study of Sb₂Se₃ thin-film solar cell,achieving the substrate configuration of Ag/ITO/ZnO/CdS/Sb₂Se₃/Mo Sb₂Se₃ thin film solar cells with a conversion efficiency of 4.25%.,The reported open-circuit voltage（Voc）of Sb₂Se₃ soalr cell is limited to ⁰.4 V with the band gap-voltage deficit（2）-(1（8?）of 0.7 V,which is unacceptable for high efficiency solar cells.Naturally,increasing the Voc becomes the key step to further improve the conversion efficiency of Sb₂Se₃ solar cell.Increasing the doping density of Sb₂Se₃ absorber layer can boost the Voc of Sb₂Se₃ solar cell.In this thesis,we firstly study the unintentional impurities in the Sb₂Se₃ thin film and then intentionally introduce dopants to improve the photoelectric performance of Sb₂Se₃-based devices.Inductively coupled plasma-optical emission spectroscopy（ICP-OES）was applied to check the impurities in the Sb₂Se₃ thin film.The result of ICP-OES measurement indicated that besides Sb and Se,there were several trace amount of impurities including Mn（240 ppm）,Fe（950 ppm）,Cr（200 ppm）,Mg（190 ppm）,and Cu（63 ppm）in the Sb₂Se₃ thin film deposited by RTE.Both Kelvin probe force microscope（KPFM）and Hall measurements revealed that Mg was largely inert while Fe introduced the donor doping.Temperature-dependent conductivity and admittance further demonstrated that Fe doping introduced two donor defect levels within the bandgap with their positions ⁰.3 eV and ⁰.4 eV below the conduction band edge.We caution that iron contamination should be minimized for high efficiency Sb₂Se₃ solar cells.Sodium has positive effect on many inorganic thin-film solar cells such as CIGS,CdTe and so on.Especially,sodium can promote the growth of CIGS grains and significantly enhance their photoelectric conversion efficiency.Interested in the effects of sodium on the grain growth and the performance of Sb₂Se₃ solar cells,we introduced the sodium into the Sb₂Se₃ thin-film by thermal evaporation.X-ray diffraction（XRD）and scanning electron microscopy（SEM）study confirmed that sodium has a negligible influence on the grain growth.Both device performance and temperature-dependent conductivity measurement showed that sodium is inert in Sb₂Se₃ solar cells.We also study the doping of Tin in Sb₂Se₃ thin film in the same way,and obtain the same result as that of sodium.