Defect Passivation for Kesterite CZTSSe Solar Cells via In Situ Al₂O₃ Incorporation into the Bulk CZTSSe Absorber

Abstract

A method for in situ Al 2 O 3 incorporation into a Cu 2 ZnSn(S,Se) 4 (CZTSSe) absorber and its effect on solar cell performance is reported. Al 2 O 3 -incorporated CZTSSe films can be prepared by spraying a precursor solution containing Al metal salt dissolved together with Cu, Zn, and Sn metal salts and thiourea. X-ray photoemission spectroscopy (XPS) and field-emission transmission electron microscopy (FESEM) reveal the existence of an Al 2 O 3 phase in the CZTSSe film. X-ray diffraction (XRD) and Raman spectroscopy indicate that Al 2 O 3 incorporation (Al: 0%-2%) does not have a noticeable effect on the crystallization process through postselenization and does not change the lattice parameters of the selenized CZTSSe. However, optimal Al 2 O 3 incorporation is found to reduce the defect level and defect density, as confirmed by various characterization methods, such as 442 nm Raman spectroscopy, photoluminescence, admittance spectroscopy, and temperature-dependent current density measurements. In addition, Al 2 O 3 incorporation reduces the Urbach energy and back-contact barrier height. Al 2 O 3 incorporation is found to induce enhancement of Na and O concentrations in the absorber, which facilitates defect passivation effects. Owing to the observed beneficial effects of Al 2 O 3 incorporation, the device performance is significantly enhanced, achieving a maximum power conversion efficiency of 11.76%.

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

“…[ 17 ] The O 2− induced by Al 2 O 3 on the surface could attract positively charged interstitial Na + . [ 12 ] After AS treatment, the peak intensity of O 2− and Se 4+ decreased significantly, which indicates the further cleaning effect of the CZTSSe surface by the AS treatment. The increased intensity of the S 2p peak after AS treatment indicates S incorporation and/or adsorption on the surface of the absorber (Figure 5f), which is considered as further passivation of the film surface.…”

“…With such method, the defect level and defect density were tailored. [ 12 ] Furthermore, our group prepared ultrathin Al 2 O 3 by the ALD on the precursor film before the selenization process. After optimizing the thickness of the Al 2 O 3 , the V OC deficit was reduced from 0.621 to 0.577 V. [ 13 ] Additionally, Hao's group systematically clarified the relationship between ALD‐Al 2 O 3 on the absorber layer and the improvement in V OC , which is accredited to the hydrogen from the ALD process and the homogeneous passivation layer on the surface of CZTS absorber.…”

Efficiency Improvement of Narrow Band Gap Cu(In,Ga)(S,Se)2 Solar Cell with Alkali Treatment via Aqueous Spray Pyrolysis Deposition

“…The full device structure was then completed with the deposition of i-ZnO (∼50 nm) and tin-doped indium oxide (ITO) (∼300 nm) layers by radio frequency (RF) magnetron sputtering. Detailed information on the buffer and window layer fabrication processes can be found elsewhere. ,,− No additional antireflection coatings were applied to the fabricated devices. For measurement of device performance, we mechanically scribed the cell with an area of 0.20 cm 2 .…”

“…With air annealing, they obtained improved crystallinity of the CISSe absorber without carbon residue near the bottom electrode, which enabled a PCE of more than ∼14%. But, all device parameters, V oc , short-circuit current density ( J sc ), and fill factor ( FF ), were lower compared to the devices made by using a vacuum-based process. ,, We have developed spray pyrolysis with deionized water (DIW) for Cu­(In,Ga)­(S,Se) 2 (CIGSSe) solar cells. ,,− DIW is the most eco-friendly, low-cost solvent, and it does not retain any kind of carbon residue in the fabricated absorber, which is usually observed when using organic solvents and can be a possible limitation to device performance. In addition, alkali doping/alloying is easily achievable by spraying an alkali-dissolved aqueous solution. , For the narrow band gap solar cells ( E g = ∼1.1 eV) on a flexible SUS substrate, spraying Na/K codissolved Cu-In-Ga-S precursor solution in an air environment (in situ alkali doping/alloying) provides a PCE of 11.45% …”

Mechanism for Improving Kesterite Solar Cells Performance via Filed Passivation Effect Induced by V‐Doped MoSe2 Interface Layer at Back Interface

“…Furthermore, the HCell-MoSe 2 :V exhibits nonlinear V OC -T characteristics from %110 K, which is much lower than HCell-Ref (%160 K), which implies HCell-MoSe 2 :V has a lower back contact barrier. [45,46] Meanwhile, it is well known that the presence of a cross-over point between the light and dark J-V curves indicates the presence of a back contact barrier [47,48] and the higher current density corresponding to the intersection points means the lower back contact barrier height. From Figure 9d, the current density corresponding to the cross-over point is increased from 65.03 to 123.99 mA cm À2 after V is incorporated into Mo and MoSe 2 films, indicating that HCell-MoSe 2 :V has a lower back contact barrier.…”