Defect Engineering in Earth‐Abundant Cu₂ZnSn(S,Se)₄ Photovoltaic Materials via Ga³⁺‐Doping for over 12% Efficient Solar Cells

Abstract

The efficiency of earth‐abundant Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is considerably lower than the Shockley–Queisser limit. One of the main reasons for this is the presence of deleterious cation disordering caused by SnZn antisite and 2CuZn+SnZn defect clusters, resulting in a short minority carrier lifetime and significant band tailing, leading to a large open‐circuit voltage deficit, and hence, low efficiency. In this study, Ga‐doping is used to increase the CZTSSe solar cell efficiency to as high as 12.3%, one of the highest for this type of cells. First‐principles calculations show that the preference of Ga3+ occupying Zn and Sn sites has a benign effect on suppressing the formation of the SnZn deep donor defects by upwardly shifting the Fermi level, which is further confirmed by deep‐level transient spectroscopy characterization. Besides, the Ga dopants can also form defect‐dopant clusters, such as GaZn+CuZn and GaZn+GaSn, which also have positive effects on suppressing the band‐tailing states. The defect engineering via Ga3+‐doping may suppress the band‐tailing defect with a decreased Urbach energy, elevate the minority carrier lifetime, and in the end, enhance the VOC from 473 to 515 mV. These results provide a new route to further increase CZTSSe‐based solar cell efficiency by defect engineering.

In‐Situ Hot Oxygen Cleansing and Passivation for All‐Inorganic Perovskite Solar Cells Deposited in Ambient to Breakthrough 19% Efficiency

“…[1] For decades, researchers have developed various thin-film solar cells with alternative light-harvesting materials including inorganic, organic, and perovskite semiconductors. [2][3][4][5][6][7][8][9] Among thin-film photovoltaic technologies, all-inorganic cesium lead halide perovskite (CsPbI 3 ) has been attracting ever-increasing attention in the last few years due to its excellent thermal stability and chemical resistance. [10][11][12] For instance, the CsPbI 3 perovskite exhibits a suitable optical band gap (E g : ≈1.7 eV) and high absorbance.…”

Optimizing the Ratio of Sn4+ and Sn2+ in Cu2ZnSn(S,Se)4 Precursor Solution via Air Environment for Highly Efficient Solar Cells

“…Figure 7d shows that the positions of the defect that E a1 and E a2 in devices A and C are relative to the valence band maximum (VBM). [ 51–53 ] In addition, device C obtained a relatively faster emission rate, according to the following formula of the emission rate of carrierwhere σ is the carrier capture cross section, υ is the mean thermal velocity, and N is the effective density of state; thus, carrier recombination could be alleviated. [ 54 ]…”

“…As a result, V OC increases due to the few recombination of carriers. [ 52,53 ] Therefore, device A performed worse than device C under the condition of the comparable short‐circuit current density. In addition, the very deep defect with E a3 of 0.691 eV may be V sn , whose concentration is in the order of 10 11 , which is far below the usual defects to be negligible.…”

Enhancing the Photovoltaic Performance of Cu2ZnSn(S,Se)4 Solar Cells with Ba Trace Doping: Large Chemical Mismatch Cation Incorporation

“…In addition, a weak peak with binding energy of 496.3 eV side of the Sn 3d 3/2 peak in both samples is the Zn L 3 M 45 M 45 Auger peak, [46] which could be detected extensively in CZTSSe absorbers. [40,47]…”