Epitaxial Cu(In,Ga)Se₂ Thin Films on Mo Back Contact for Solar Cells

Abstract

Single crystal Mo thin films are successfully grown on single-crystal sapphire {0001} substrates using a newly developed two-step sputtering method. Cu(In 1-x ,Ga x )Se 2 (CIGS) thin films are then epitaxially grown on the Mo thin films by three-stage co-evaporation. Following that, a CdS buffer layer is deposited on the epitaxial (epi)-CIGS thin films by a chemical bath deposition (CBD) method, leading to the overall epitaxial relations such as CdS{111}// CIGS{112}//MoSe 2 {0001}//Mo{110}//sapphire {0001}. The Cd-diffusion into the CIGS occurs to approximately 30 nm from the CIGS/CdS interface boundary together with depleted Cu at the CIGS surface region. This suggests that Cd diffuses through Cu vacancies in the intra-grain rather than at the grain boundaries. Two distinct solar cells are fabricated using epi-and polycrystalline (poly)-CIGS thin films deposited on sapphire substrates in the same deposition run. The open-circuit-voltage (V OC ) of epi-CIGS solar cell is found to be higher than poly-CIGS solar cell. The net carrier concentration (N CV ) derived from the capacitance-voltage (C-V) measurements of epi-CIGS solar cell is 3.5 times higher than poly-CIGS solar cell, suggesting one of the causes of higher V OC . This large difference in the N CV is discussed based on the results of low-temperature photoluminescence measurements.

Over 100 mVVOCImprovement for Rear Passivated ACIGS Ultra‐Thin Solar Cells

“…In previous works, the MoSe 2 growth has been found to be dependent on several factors such as substrate temperature, the Mo structural properties, (A)CIGS‐based layer deposition method, and even Na availability. [ 37–40,44,45 ] The observed MoSe 2 structure was previously related to CIGS solar cells with higher values of contact resistance, in comparison to random‐oriented MoSe 2 . [ 37,46–48 ] Nonetheless, Zhang et al showed that a solar cell containing a MoSe 2 layer with a perpendicular c‐axis orientation concerning the Mo surface significantly outperforms a device without this interface layer.…”

Impacts of KF Post-Deposition Treatment on the Band Alignment of Epitaxial Cu(In,Ga)Se2 Heterojunctions

“…Chalcopyrite CuIn x Ga 1– x Se 2 (CIGSe) thin films have been studied for solar cell applications because of their high absorption coefficient. , Contrary to Si and GaAs solar cells, the performances of polycrystalline CIGSe (poly-CIGSe), despite including grain boundaries (GBs), are significantly higher than those of epitaxial CIGSe (epi-CIGSe). − The peculiarity of CIGSe films is that higher performance devices use polycrystalline films instead of single crystals, which is in stark contrast to solar cells based on silicon or III–V materials. This outcome has led to the hypothesis that grain boundaries in CIGS films may either be benign or beneficial to device performance …”

Electrical characterisation and analysis of dominant contributions in disordered semiconducting systems with an application to the pure bentonite material for civil engineering applications

“…Copper ternary chalcopyrite compounds of the family of {Cu, In, Se} such as CuInSe 2 and Cu 5 In 9 Se 16 with an energy gap and high absorption coefficient of the order of 1 eV and 10 5 cm -1 may act as an absorber in thin film solar cell [1,2,[7][8][9][10][11][12] devices. On the other hand, a variety of nanoparticles of semiconductors, for example TiO 2 and ZnO, can be incorporated into clay minerals.…”