Quasi One Dimensional Antimony Selenide Thin Film Solar Cells for Next Generation Photovoltaics

Pedro Vidal Fuente

Saucedo Silva, Edgardo Izquierdo Roca, Víctor

This doctoral thesis explores the quasi-one-dimensional absorber material Sb2Se3 and its application in thin-film solar cells in a SLG/Mo/Sb2Se3/CdS/i-ZnO/ITO substrate configuration. First, characterization mechanisms based on Raman spectroscopy and X-ray diffraction techniques are developed to evaluate the basic physicochemical properties of the Sb2Se3 material and generate fundamental knowledge to adequately identify the phase and possible secondary phases obtained during the synthesis process of the thin films. 27 of the 30 theoretically predicted Raman peaks are identified by multi-wavelength and low-temperature Raman spectroscopy measurements, correlating with the observed XRD pattern and its difference between the as-grown and single-crystalline films. Based on the developed methodology, mechanisms for controlling the quality of the layers by non-invasive methods are proposed that allow for rapid and non-invasive analysis. In a second step, the synthesis route of Sb2Se3 is explored through a two-step sequential process based on the reactive annealing in a low selenium atmosphere of a previously physically evaporated antimony metal layer. The study focuses on the effects of temperature, time and pressure of the reactive annealing process and how these affect the final composition ratio of the Sb2Se3 system, reflected in an optimal range of values ​​of the ratio 3[Sb]/2[Se] = 0.8 - 0.9 and thus obtaining a maximum device efficiency of 5.7%. This development of the devices has been carried out through highly industrializable processes based on a sequential low-temperature route and substrate structure, which allows the adaptation to different substrates, both rigid like glass, flexible like thin steel sheets or flexible and transparent like polymers. These devices are studied and analyzed in more depth to reveal the limiting factors present that are mainly found in the device interfaces. Finally, a deeper investigation of the devices already optimized in terms of stability under temperatures between T = 50 - 350 °C is carried out. This study highlights a high instability in Sb2Se3 at temperatures as low as 50 °C, mainly reflected in the reduction of the volume of the unit cell of the Sb2Se3 system and its correlation with the decrease of the optoelectronic parameters obtained. Instability studies of emerging materials are fundamental for their rapid industrialization as they avoid future problems of adaptation to industrial processes and guide future research in a logical and coherent sense. The development of this Thesis has resulted in the collaboration of the A Prop-IREC center with other research centers, universities and companies in 4 European and National projects that are based on or use/expand the results presented here: SENSATE European Research Council (ERC) (Grant Agreement No 866018); MATER-ONE MICINN-AEI (requests 2020) (PID2020-116719RB-C42); HIDDEN-PV Submitted to the M-era.net 2022 call, which has passed the preselection step; FOTO-CER (MIG-20211047, Missions CDTI 2021).

The results achieved in this thesis made the technology very attractive for its industrialization due to these key aspects: i) it is based on inorganic materials and is free of critical raw materials which is crucial to ensure a high stability and long-term sustainability; ii) contrarily to the standard of the Sb2Se3 technological development, it has a substrate configuration, it is produced in a sequential process by scalable physical deposition techniques and at low synthesis temperatures and it can be fabricated on flexible polymeric and metallic substrates; and iii) it can be tuned by the adaptation of the Sb2Se3 technology to Sb2S3. The relevance of the research in the field is reflected in the 73 accumulated citations in high impact factor journals. These results provided the SEMS research group in IREC new expertise that permitted the participation in several international conferences and national and European projects, generating networks with relevant research centers and industries for the application of the results to relevant environments. In this regard, the characteristics of the developed technologies, makes it compatible with advanced integrated PV applications in growing market niches such as indoor PV, the powering of internet of things (IoT) devices, building-integrated PV (BIPV), vehicle-integrated PV (VIPV), Agrivoltaics (APV)…

Quasi-one-dimensional absorber material; Sb2Se3; Thin-film solar cells; SLG/Mo/Sb2Se3/CdS/i-ZnO/ITO; Raman spectroscopy; X-ray diffraction; Physicochemical properties; Phase identification; Secondary phases; Thin-film synthesis; Multi-wavelength Raman; Low-temperature Raman; XRD pattern; As-grown films; Single-crystalline films; Non-invasive quality control; Rapid analysis; Two-step sequential process; Reactive annealing; Physically evaporated antimony; Low selenium atmosphere; Temperature effects; Time effects; Pressure effects; Composition ratio; 3[Sb]/2[Se] ratio; Device efficiency; Highly industrializable processes; Low-temperature route; Substrate structure; Rigid substrates; Flexible substrates; Transparent substrates; Glass; Thin steel sheets; Polymers; Limiting factors; Device interfaces; Stability under temperature; Unit cell volume reduction; Optoelectronic parameters; Instability studies; Industrialization; Future research; A Prop-IREC; Research collaborations; European projects; National projects; SENSATE European Research Council (ERC); MATER-ONE MICINN-AEI; HIDDEN-PV; FOTO-CER.