EST. 2022

Band Alignment and Interface Engineering

Solar photovoltaic (PV) materials generate electron−hole pairs upon light absorption followed by electricity generation in a device architecture. Our work involves working on the different strategies to dramatically increase the efficiency and lower the cost of the solar energy. The different physical and chemical properties of interfacial layers often cause unfavourable band alignment and interfacial states that leads to high carrier recombination and eventually results in lower device efficiency. The trap-assisted tunnelling along with the buffer/absorber interface recombination are introduced as the most important loss mechanisms in solar cells. The detailed experimental understanding of the loss mechanisms and the band alignments leading to solar cell device fabrication remains elusive. The most important loss mechanisms include: (a) buffer/absorber interface losses; (b) diffusion losses; (c) non-radiative losses; (d) thermionic emission losses; (e) radiative losses; (f) trap assisted tunnelling losses. Under this research theme, our goal is to employ the experimental methods to engineer the optical and structural properties of the semiconducting materials to reduce recombination due to the interface trap states. Carrier management through interface engineering via emerging materials will help to achieve ultra-high efficiency in perovskites and earth-abundant material based solar cells.

Cu2SnS3 Material: Ternary Cu2SnS3 (CTS) is an attractive nontoxic and earth abundant absorber material with suitable optoelectronic properties for cost effective photoelectrochemical application. A staggered gap (type II) band alignment is found at the CTS/ CdS interface, whereas a straddling gap (type I) band alignment is observed at the CTS/ZnS interface. The conduction band offset (CBO) at the CTS/CdS and CTS/ ZnS interface is estimated at 0.08 and 0.29 eV, respectively. The conduction band minimum (CBM) of CTS was found to be higher than that of CdS and lower than that of ZnS. The very small conduction band offset (CBO) of 0.08 eV measured at the CTS/CdS heterojunction is an encouraging factor for PEC cell energy conversion efficiency.

Cu2NiSnS4 Material: We have synthesized Cu2NiSnS4 nanocrystals and thin films in a novel zincblende type cubic phase using a facile hot-injection method. The structural, electronic, and optical properties are studied using various experimental techniques, and the results are further corroborated within first-principles density functional theory-based calculations. The band alignments for both conduction and valence bands are directly measured. The 1.47 eV electrochemical gap and very small conduction band offset of 0.12 eV measured at the CNTS/CdS heterojunction are encouraging factors for the device. These results enable us to model carrier transport across the heterostructure interface.