Identifying the origin of the V_oc deficit of kesterite solar cells from the two grain growth mechanisms induced by Sn²⁺ and Sn⁴⁺ precursors in DMSO solution

Abstract

Kesterite Cu2ZnSn(S,Se)4 solar cells fabricated from DMSO molecular solutions exhibit very different open circuit voltage (Voc) when tin precursor has different oxidation state (Sn2+ vs Sn4 ). Here, the grain...

Ag Incorporation with Controlled Grain Growth Enables 12.5% Efficient Kesterite Solar Cell with Open Circuit Voltage Reached 64.2% Shockley–Queisser Limit

“…Precursor solutions with different Ag concentration, Ag/(Cu + Ag) = 0%, 5%, 10%, 15%, 30%, 50%, 80%, and 100%, were made by dissolving AgNO 3 , CuCl, Zn(OAc) 2 , SnCl 4 , and Tu in DMSO according to our previous report. [ 32,33 ] All the solutions had a Cu or (Ag + Cu) poor and Zn rich composition with the mole ratios of (Ag + Cu)/(Zn + Sn) = 0.75 and Zn/Sn = 1.05. The precursor films were fabricated from these solutions and annealed with Se (selenization) to form absorber films through the same procedure as CZTSSe except for AZTSSe.…”

“…The precursor films were fabricated from these solutions and annealed with Se (selenization) to form absorber films through the same procedure as CZTSSe except for AZTSSe. [ 32,33 ] The selenization temperature for AZTSSe was 500 °C instead of 550 °C to avoid decomposition. [ 22,25 ] For the convenience of description in the following discussion, samples are named CZTS, ACZTS‐ n , and AZTS for precursor and CZTSSe, ACZTSSe‐ n , and AZTSSe for absorber films, n denotes the percentage of Ag to (Cu + Ag) in the precursor solutions.…”

“…We have recently reported that CZTSSe absorbers can be grown from a dimethyl sulfoxide (DMSO) solution‐processed precursor film through a direct kesterite phase conversion grain growth mechanism. [ 32,33 ] By using SnCl 4 as Sn precursor and CuCl, Zn(OAc) 2 , and thiourea (Tu), respectively, as Cu, Zn, and S precursor, a uniform kesterite (CZTS) structured precursor film was fabricated from the DMSO solution, and importantly, this precursor film directly converted to large grain CZTSSe absorber during selenization without going through secondary phases as similarly fabricated precursor film using SnCl 2 ·2H 2 O as Sn precursor. [ 32,33 ] A CZTSSe solar cell with an efficiency of 12.4% and a V oc of 0.522V was obtained from Sn 4+ solution‐based absorber, which was much higher than similar fabricated absorber from Sn 2+ solution that took multiphase fusion grain growth mechanism.…”

“…[ 32,33 ] By using SnCl 4 as Sn precursor and CuCl, Zn(OAc) 2 , and thiourea (Tu), respectively, as Cu, Zn, and S precursor, a uniform kesterite (CZTS) structured precursor film was fabricated from the DMSO solution, and importantly, this precursor film directly converted to large grain CZTSSe absorber during selenization without going through secondary phases as similarly fabricated precursor film using SnCl 2 ·2H 2 O as Sn precursor. [ 32,33 ] A CZTSSe solar cell with an efficiency of 12.4% and a V oc of 0.522V was obtained from Sn 4+ solution‐based absorber, which was much higher than similar fabricated absorber from Sn 2+ solution that took multiphase fusion grain growth mechanism. [ 32,33 ] Here, we report that Ag can be incorporated into the lattice of kesterite by the same reaction path as CZTSSe and high quality ACZTSSe solid solutions with the whole concentration of Ag have been fabricated.…”

“…[ 32,33 ] A CZTSSe solar cell with an efficiency of 12.4% and a V oc of 0.522V was obtained from Sn 4+ solution‐based absorber, which was much higher than similar fabricated absorber from Sn 2+ solution that took multiphase fusion grain growth mechanism. [ 32,33 ] Here, we report that Ag can be incorporated into the lattice of kesterite by the same reaction path as CZTSSe and high quality ACZTSSe solid solutions with the whole concentration of Ag have been fabricated. With 5% Ag incorporation (ACZTSSe‐5), a champion device with an efficiency of 12.5% (without antireflection coating, active area efficiency 13.5%), a FF of 72.0%, and a V oc of 0.540 V has been achieved.…”