KCN Chemical Etching of van der Waals Sb2Se3 Thin Films Synthesized at Low Temperature Leads to Inverted Surface Polarity and Improved Solar Cell Efficiency.

Recent developments in Sb2Se3 van der Waals material as an absorber candidate for thin film photovoltaic applications have demonstrated the importance of surface management for improving the conversion efficiency of this technology. Sb2Se3 thin films' versatility in delivering good efficiencies in both superstrate and substrate configurations, coupled with a compatibility with various low-temperature deposition techniques (below 500 °C and often below 350 °C), makes them highly attractive for advanced photovoltaic applications. This study presents a comparative analysis of the most effective chemical etchings developed for related thin film chalcogenide technologies to identify and understand the most appropriate surface chemical treatments for Sb2Se3 in substrate configuration, synthesized using a sequential process at very low temperatures (320 °C). Eight different chemical etchings were tested and investigated, and the results show that only KCN-based solutions lead to an improvement in the solar cell's performance, primarily due to an increase in the fill factor. Surface analysis of the samples shows that KCN etching produces very Sb-rich surfaces that do not affect the properties of the bulk. It is proposed that this Sb-rich interface inverts the surface polarity, creating a "buried junction" with CdS, thereby explaining the improvement of the fill factor of the devices, as confirmed by device modeling. The results of this study underscore the importance of surface management in low-temperature synthesized Sb2Se3 absorbers, where Sb-rich interfaces are crucial for achieving high-efficiency devices. This research contributes to ongoing efforts to improve the performance of Sb2Se3 thin film photovoltaic technology and could pave the way for the development of more efficient solar cells with optimized interfaces.

Poly(amidoamine) Dendrimer as an Interfacial Dipole Modification in Crystalline Silicon Solar Cells.

Poly(amidoamine) (PAMAM) dendrimers are used to modify the interface of metal-semiconductor junctions. The large number of protonated amines contributes to the formation of a dipole layer, which finally serves to form electron-selective contacts in silicon heterojunction solar cells. By modification of the work function of the contacts, the addition of the PAMAM dendrimer interlayer quenches Fermi level pinning, thus creating an ohmic contact between the metal and the semiconductor. This is supported by the observation of a low contact resistivity of 4.5 mΩ cm2, the shift in work function, and the n-type behavior of PAMAM dendrimer films on the surface of crystalline silicon. A silicon heterojunction solar cell containing the PAMAM dendrimer interlayer is presented, which achieved a power conversion efficiency of 14.5%, an increase of 8.3% over the reference device without the dipole interlayer.

Does Sb2Se3 Admit Nonstoichiometric Conditions? How Modifying the Overall Se Content Affects the Structural, Optical, and Optoelectronic Properties of Sb2Se3 Thin Films.

Sb2Se3 is a quasi-one-dimensional (1D) semiconductor, which has shown great promise in photovoltaics. However, its performance is currently limited by a high Voc deficit. Therefore, it is necessary to explore new strategies to minimize the formation of intrinsic defects and thus unlock the absorber's whole potential. It has been reported that tuning the Se/Sb relative content could enable a selective control of the defects. Furthermore, recent experimental evidence has shown that moderate Se excess enhances the photovoltaic performance; however, it is not yet clear whether this excess has been incorporated into the structure. In this work, a series of Sb2Se3 thin films have been prepared imposing different nominal compositions (from Sb-rich to Se-rich) and then have been thoroughly characterized using compositional, structural, and optical analysis techniques. Hence, it is shown that Sb2Se3 does not allow an extended range of nonstoichiometric conditions. Instead, any Sb or Se excesses are compensated in the form of secondary phases. Also, a correlation has been found between operating under Se-rich conditions and an improvement in the crystalline orientation, which is likely related to the formation of a MoSe2 phase in the back interface. Finally, this study shows new utilities of Raman, X-ray diffraction, and photothermal deflection spectroscopy combination techniques to examine the structural properties of Sb2Se3, especially how well-oriented the material is.