The CdS layer was formed by chemical bath deposition with 30 nm of thickness. Open circuit voltage (V oc) of the cell is small due to its low band gap and probably interface band-off between CdS and CZTSSe and the fill factor (FF) is relatively

small because its carrier path and surface serial resistance are not defined well [24]. To obtain the high-efficiency solar cells, we need to improve V oc and FF. Table 1 Device performances and composition of CZTSSe thin-film solar cell Sample V oc (mV) J sc (mA/cm2) F.F. (%) Eff. (%) Cu/Zn + Sn Zn/Sn CZTSSe 349.00 30.61 46.13 4.93 0.94 1.65 Figure  2 shows topography, surface potential, and the line profiles of the CZTSSe thin film. Grains Osimertinib in vivo of the CZTSSe films are shown in Figure  2a. The grains seem to possess small particulates. In Figure  2b, yellow region represents positive potential value and blue region indicates negative potential value. The one-dimensional line profiles in Figure  2c project the blue line of Figure  2a,b. In Figure  2c, the CZTSSe Volasertib manufacturer thin film reveals high positive surface potential near GBs. CIGS thin films form

positively charged GBs which is related to negative band bending. The negative energy bending near GBs improves carrier separation and suppresses recombination of electron–hole pairs at GBs [14, 15] because holes tend to be kept away from the GB region. However, the minority-carrier electrons are moving into the GBs, which might be a trade-off for carrier migration to the electrodes. It is desirable to study carrier Selumetinib purchase transport in the intragrains (IGs) as well as the GBs. Surface potential distribution in the CZTSSe thin film shows similar behaviors to the CIGS

thin films. The potential near GBs in the CZTSSe thin film indicates about 300 mV and negative potential about −100 to −200 mV at IGs, which is linked to negative band bending on GBs of the CZTSSe thin film. This is consistent with the fact that some of the minority carriers (electron) transferred to and collected at GBs in the CZTSe thin film [25]. Thus, electron–hole carriers separate effectively on GBs of CZTSSe thin film not acting as recombination center, which is a similar phenomenon occurring in CIGS. In order to clarify the relationship between topography and surface potential, we introduce a topographic parameter Φ = d 2 H/dX 2. H is the height and X is the lateral see more direction. So the second derivative of H with respect to X means the concave or the convex shapes of the surface topography. Since Φ is an indicative of the surface alterations of the films, we can expect the positive value as GBs and the negative as IGs. From this parameter, we are able to ascertain roughly the region of GBs on the surface. Some groups claim that additional information like electron beam backscattered diffraction (EBSD) is required to confirm the granular nature of the local regions [26]. However, our approach is also widely acceptable for inspection of the surface topography and potential.