TiN Interlayers with Varied Thickness in Cu_2ZnSnS(e)_4 Thin Film Solar Cells: Effect on Na Diffusion, Back Contact Stability, and Performance

摘要

In this study, interlayers with varied thickness of TiN between Cu_2ZnSnS(e)_4(CZTS(e)) absorbers and Mo on soda-lime glass substrates are investigated forCZTS(e) thin film solar cells. Na diffusion is analyzed using Secondary Ion MassSpectrometry and it is found that the use of thick TiN interlayers facilitates Nadiffusion into the absorbers. The CZTS(e)/TiN/Mo interfaces are scrutinized usingTransmission Electron Microscopy (TEM) Electron Energy Loss Spectroscopy(EELS). It is found that diffusion of chalcogens present in the precursor occursthrough openings, resulting from surface roughness in the Mo, in the otherwisechemically stable TiN interlayers, forming point contacts of MoS(e)_2. It is furtherestablished that both chalcogens and Mo diffuse along the TiN interlayer grainboundaries. Solar cell performance for sulfur-annealed samples improved withincreased thickness of TiN, and with a 200 nm TiN interlayer, the solar cellperformance is comparable to a typical Mo reference. Pure TiN bulk contacts areinvestigated and shown to work, but the performance is still inferior to the TiNinterlayer back contacts. The use of thick TiN interlayers offers a pathway toachieve high efficiency CZTS(e) solar cells on highly inert back contacts.