Enhancing Surface Properties for Electrodeposited Cu(In,Ga)Se₂ Films by (NH₄)₂S Solution at Room Temperature

Abstract

Fabricating chalcopyrite Cu­(In,Ga)­Se2 (CIGS) films from electrodeposition is one of the most effective ways to lower the production cost and energy consumption compared with that from vacuum methods. However, this process often produces a pronounced rough surface with impurity phases, induces the accumulation of gallium, and results in a low surface band gap. In this work, ammonium sulfide ((NH4)2S, AS) solution treatment is used as a single way to realize the optimization of the distribution of elements on the CIGS surface. It is revealed that this room-temperature process not only significantly reduces the surface roughness (R a) but also incorporates sulfur (S) into the CIGS film successfully. An appropriate AS treatment duration can effectively remove the impurity phases and reduce the series resistance, and thus the dominant recombination moves from the CdS/CIGS heterojunction interface to the bulk. Consequently, the open-circuit voltage (V OC) and fill factor (FF) of solar cells have been greatly improved (from 484 to 532 mV, from 62.52 to 68.15%), leading to higher efficiency of 11.92%. This work focuses on revealing the etching mechanism of the CIGS films by the AS treatment at room temperature.

Band Gap Engineering in Quadruple-Layered Sillén–Aurivillius Perovskite Oxychlorides Bi7Fe2Ti2O17X (X = Cl, Br, I) for Enhanced Photocatalytic Performance

“…It is observed also that, the order of light response intensities is BFTOC > BFTOB > BFTOI, which can be ascribed to the sub-band gap absorption of powder materials. As we know, the significant sub-band gap absorption of films is indicative of the presence of the secondary phases or the band tailing [44][45][46][47]. This observation suggests the BFTOC powder has the lowest defect concentrations and photogenerated carrier recombination compared with the two other samples, which should be the reason for the highest performance of CO2 reduction for BFTOC sample, as is consistent with the SEM results.…”

Toward High Efficient Cu2ZnSn(Sx,Se1−x)4 Solar Cells: Break the Limitations of VOC and FF

“…According to the report from Buffière et al., the AS solution treatment was performed on the CIGSe absorber, and the increasing of the Cu 2p peak intensity is related to the slow etching rate of the Cu‐related phase by the AS treatment. [ 17,21 ] Furthermore, for the Zn 2p3/2 peak, a significant banding energy decrease of 0.15 eV is obtained after the AS treatment, and the Sn 3d5/2 peak shifted 0.2 eV toward low binding energy, from 486.5 eV for sample Kes and Kes‐Al 2 O 3 to 486.3 eV for sample Kes‐Al 2 O 3 ‐AS. According to Grenet et al., the peaks of Zn 2p3/2 and Sn 3d5/2 moving toward lower binding energy after AS treatment is considered to be due to the oxidation/deoxidation of the ZnSe and SnSe x phases on the surface, respectively.…”

“…It is reported that ammonium sulfide ((NH 4 ) 2 S, referred to as AS) solution treatment on the absorber layer can improve the film's surface properties. [16][17][18][19][20][21][22][23] For example, Buffière et al selectively removed the secondary phase on the surface and modified the surface chemical state by dipping CIGS absorber into AS solution, and the minority carrier lifetime increased about 6-11 ns with different treatment times. [17] The same treatment has been employed for CZTSSe, too.…”

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

“…The relevance of the development of low temperature synthetic procedures of Sb 2 Se 3 is supported by its versatility in terms of device processing, making this material an ideal candidate for temperature-sensitive applications such as tandem solar cells and flexible or transparent substrates. The different etching solutions investigated in this work have been inspired by processes already evaluated and proven effective in other thin film technologies, in particular, HNO 3 -H 3 PO 4 (NP) and Br 2 -methanol (BrM) in CdTe; , KCN, (NH 4 ) 2 S (NHS), and BrM in CIGS; ,− and KCN, NHS, BrM, KMnO 4 -H 2 SO 4 (KMO), and CS 2 in kesterite, ,− as presented in Table . For all of these chemical solutions, the initial etching conditions were selected from the optimal ones reported in the literature, and a complementary study was performed by varying the etchant concentration and etching times.…”

“…Reduces the surface roughness (better covered by CdS) but also incorporates sulfur (increased bandgap) and removes the impurity phases (reduction of the acceptor Cu-Ga). 32,33 It reduces series resistance, and consequently increases V oc , FF, and efficiency. defects.…”