Toward High Efficient Cu₂ZnSn(S_x,Se_1−x)₄ Solar Cells: Break the Limitations of V_OC and FF

Abstract

Increasing the fill factor (FF) and the open‐circuit voltage (VOC) simultaneously together with non‐decreased short‐circuit current density (JSC) are a challenge for highly efficient Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Aimed at such target in CZTSSe solar cells, a synergistic strategy to tailor the recombination in the bulk and at the heterojunction interface has been developed, consisting of atomic‐layer deposited aluminum oxide (ALD‐Al2O3) and (NH4)2S treatment. With this strategy, deep‐level CuZn defects are converted into shallower VCu defects and improved crystallinity, while the surface of the absorber is optimized by removing Zn‐ and Sn‐related impurities and incorporating S. Consequently, the defects responsible for recombination in the bulk and at the heterojunction interface are effectively passivated, thereby prolonging the minority carrier lifetime and increasing the depletion region width, which promote carrier collection and reduce charge loss. As a consequence, the VOC deficit decreases from 0.607 to 0.547 V, and the average FF increases from 64.2% to 69.7%, especially, JSC does not decrease. Thus, the CZTSSe solar cell with the remarkable efficiency of 13.0% is fabricated. This study highlights the increased FF together with VOC simultaneously to promote the efficiency of CZTSSe solar cells, which could also be applied to other photoelectronic devices.

Passivating SnZn Defect and Optimizing Energy Level Alignment via Organic Silicon Salt Incorporation toward Efficient Solution‐Processed CZTSSe Solar Cells

“…The main Raman peaks located at 172, 197, and 234 cm −1 were allocated to the kesteritebased CZTSe phase, and the peak in the vicinity of 329 cm −1 should be attributed to kesterite-based CZTS phase, which is in agreement with the published literature. [30,31,35] Apart from those, no other peaks appeared in any of the samples. Raman analysis further confirmed that no peaks of the impurity phases were detected in any of the CZTSSe-based thin films.…”

“…Additionally, for the three samples, the peak positions of Cu 2p, Zn 2p, and Sn 3d are assigned to +1, +2, and +4 states, respectively. [30,35] As is well-known, the electrical features of the CZTSSe grain boundaries (GBs) play a pivotal role in the transport of carriers, thereby affecting the photovoltaic performance of devices. [54][55][56][57] Kelvin probe force microscopy (KPFM) measurements were conducted to analyse the behaviors of carriers in the CZTSSe-based absorber layer without and with Si substitution, as illustrated in Figure 4.…”

“…Apart from the antisite defects in the absorber, the energy level misalignment at the CdS/CZTSSe heterojunction interface caused by the narrow bandgap (E g ) of CZTSSe absorber also results in undesired charge accumulation and blocks carrier extraction, by which higher V oc is unattainable. [16][17][18]30] Hence, rational management of the Sn Zn -related defects in the absorber and the energy level alignment between CdS/CZTSSe interface are urgently needed to mitigate the V oc deficit for yielding highperformance CZTSSe solar cells.…”

Improving the Device Performance of CZTSSe Thin-Film Solar Cells via Indium Doping

“…So far, successful incorporation of Cd 2+ and Mn 2+ isovalent cations has been achieved in the promising results in CZTSSe TFSCs that mitigate Zn-related defects. − However, their performance remains relatively low compared with CIGSSe-based TFSCs. Apart from this, many efforts have been dedicated to achieving low V oc -deficit characteristics in kesterite TFSCs. , Guo et al showed that controlling selenization pressure during the annealing process enables enhanced performance in the CZTSSe TFSCs. Zhang et al also showed that creating a microenvironment with SnSe 2 vapor and preselenization of the surface and back contact can effectively improve the device performance.…”

“…Apart from this, many efforts have been dedicated to achieving low V oc -deficit characteristics in kesterite TFSCs. 12,13 Guo et al 14 showed that controlling selenization pressure during the annealing process enables enhanced performance in the CZTSSe TFSCs. Zhang et al 15 also showed that creating a microenvironment with SnSe 2 vapor and preselenization of the surface and back contact can effectively improve the device performance.…”