Doping Behavior of Zn in CdS and Its Effect on the Power Conversion Efficiency of the Cu₂ZnSn(S, Se)₄ Solar Cell

Abstract

High carrier recombination at the Cu2ZnSn (S, Se)4(CZTSSe)/CdS interface is the critical issue that results in the low power conversion efficiency (PCE) of CZTSSe solar cells. To reduce the recombination by optimizing the CZTSSe/CdS interfacial structure, we fabricated a Zn doped CdS (Zn x Cd1 – x S) thin film with x of 0–0.32 and a CZTSSe solar cell with the Zn x Cd1 – x S as the buffer layer. It is found that Zn substitutes for Cd in the x range of 0–0.26 and that some of the Zn substitutes for Cd and another Zn locates in the interstitial site of the CdS lattice in the x range of 0.26–0.32, which make the lattice mismatch between CZTSSe and Zn x Cd1 – x S decrease in x of 0–0.26 and increase in x of 0.26–0.32. The conduction band offset at the CZTSSe/Zn x Cd1 – x S interface is demonstrated by XPS to be a positive ″spike″-like type and increases from 0.11 to 0.43 eV as x increases from 0 to 0.32. PCE is increased from 5.00 to 7.73% by optimizing x. The increased PCE is attributed to increased open-circuit voltage (V OC) and filling factor (FF), while the decreased PCE is due to decreased V OC, FF, and J SC. By using quantitative analysis methods, the increased V OC and FF are mainly attributed to the increased shunt resistance (R sh) and decreased reverse saturation current density (J 0), and the decreased short-circuit current density (J SC) is attributed to the increased conduction band offset (CBO). The influence mechanism of Zn doping on R sh, J 0, and CBO is discussed.

Performance Degradation in Solution-Processed Cu2ZnSn(S,Se)4 Solar Cells Based on Different Oxidation States of Copper Salts

“…According to theory, the PCE is defined as where P in represents the incident light power. The contribution percentages of V OC , J SC , and FF to the change in PCE for the Cu 2+ -cell and Cu + -cell is calculated by combining eq and the approach reported, as shown in Figure a and Table S3. The increased PCE for is mostly due to the increased V OC and J SC , while the increase in FF has nearly no effect on the increase in PCE.…”

“…The relationship between V OC and the electrical parameters ( R sh , J L , and ( A , J 0 )) can be expressed by the formula where q (1.6 × 10 –19 C), k , and T represent the electron charge, Boltzmann constant, and temperature, respectively. The contribution percentage of J L , R sh , and ( A , J 0 ) to the change in V OC of the Cu 2+ -cell and Cu + -cell is estimated by utilizing eq and the approach reported, as shown in Figure b and Table S4. The increased V OC for is mainly induced by the decrease in ( A , J 0 ), and the influence of the increase in J L and R sh on the increased V OC is less significant than that of the decrease in ( A , J 0 ) on the increased V OC .…”

“…It is well-known that the definition of FF is where V m and J m are the voltage and current density correspondeing to the maximum output power, respectively. The contribution percentage of J L , R sh , R s , and ( A , J 0 ) to the change in FF for the Cu + -cell and Cu 2+ -cell is calculated by using eqs and and the approach reported, as shown in Figure c and Table S5. The increased FF for dominantly comes from the decreased ( A , J 0 ), followed by the increased R sh , while the decrease in R s and the increase in J L almost make no contribution to the increase in FF.…”

Gradient Conduction Band Energy Engineering Driven High‐Efficiency Solution‐Processed Cu2ZnSn(S,Se)4/ZnxCd1–x S Solar Cells

“…[15,20] Recently, Zhang et al prepared pure phase Zn x Cd 1−x S through CBD method, and they regulated the CBO at the CZTSSe/Zn x Cd 1-x S interface from 0.11 to 0.43 eV by changing the Zn content to enhance the PCE from 5.00 to 7.73%. [14] It was noteworthy that while Hao and Zhang's work demonstrated increased spectral response in the short wavelength region, the Jsc decreased in both instances. [14,15] For the Hao's work, the shorter minority carrier collecting length, which resulted from the low doping level in Zn x Cd 1-x S, was assigned to the poor J SC .…”

Modulation Effect of the Zn/Sn Ratio on Performance of Chloride-Fabricated CZTSSe Cells for Boosting 10%-Beyond Efficiencies

“…As the most competitive and promising candidate for high efficient photovoltaic deployment, kesterite sulfoselenide Cu 2 ZnSn­(S,Se) 4 (CZTSSe) has received continuous attention owing to its unique advantages of abundant nontoxic elements, a high absorption coefficient of >10 4 cm –1 , and a tunable band gap in the range of 0.95∼1.5 eV. − Even though the current record power conversion efficiency (PCE) has reached 13.0%, it is still far below its theoretical efficiency, and further breakthroughs are needed in device performance . Lots of research studies aimed at improving the performance of the absorber layers to enhance the device efficiency, including optimizing the precursor solution solvent, − improving the processing technologies, , post-treating the absorber surface, , doping elements, − and adjusting the element valence and also the element composition ratios. − Nonetheless, in-depth research efforts are still required to improve device performance.…”