Defect Control for 12.5% Efficiency Cu₂ZnSnSe₄ Kesterite Thin‐Film Solar Cells by Engineering of Local Chemical Environment

Abstract

over 30% detailed balance limiting efficiency, as well as to its earth-abundant and environment-benign constituents. [1-3] The increase in power conversion efficiency to a record of 12.6% in the last decade has demonstrated the huge potential of these materials. [4,5] However, as one of the most complicated compound semiconductors, kesterite has much more intricate defect chemistry than its counterparts, Cu(In,Ga)Se 2 (CIGS) and CdTe, [6-8] making the control of intrinsic defects a major challenge. Deep intrinsic defects like Sn Zn antisites and related [Cu Zn +Sn Zn ] clusters act as deep recombination centers, leading to the short carrier lifetime. [7,9,10] Additionally, the large population of defect clusters like [2Cu Zn +Sn Zn ] introduces considerable potential (i.e., band or electrostatic) fluctuation. [11] Consequently, the performance of CZTSSe solar cells are currently stagnated by the large open-circuit voltage (V OC) deficit. [12,13] To address the detrimental intrinsic defects and defect clusters in CZTSSe absorber, multiple strategies have been employed. As suggested by the first-principle calculations, the formation energy of intrinsic defects and Kesterite-based Cu 2 ZnSn(S,Se) 4 semiconductors are emerging as promising materials for low-cost, environment-benign, and high-efficiency thin-film photo voltaics. However, the current state-of-the-art Cu 2 ZnSn(S,Se) 4 devices suffer from cation-disordering defects and defect clusters, which generally result in severe potential fluctuation, low minority carrier lifetime, and ultimately unsatisfactory performance. Herein, critical growth conditions are reported for obtaining high-quality Cu 2 ZnSnSe 4 absorber layers with the formation of detrimental intrinsic defects largely suppressed. By controlling the oxidation states of cations and modifying the local chemical composition, the local chemical environment is essentially modified during the synthesis of kesterite phase, thereby effectively suppressing detrimental intrinsic defects and activating desirable shallow acceptor Cu vacancies. Consequently, a confirmed 12.5% efficiency is demonstrated with a high V OC of 491 mV, which is the new record efficiency of pure-selenide Cu 2 ZnSnSe 4 cells with lowest V OC deficit in the kesterite family by E g /q-Voc. These encouraging results demonstrate an essential route to overcome the long-standing challenge of defect control in kesterite semiconductors, which may also be generally applicable to other multinary compound semiconductors.

Defect Control for High‐Efficiency Cu2ZnSn(S,Se)4 Solar Cells by Atomic Layer Deposition of Al2O3 on Precursor Film

“…This will be beneficial for reducing the formation of detrimental Cu Zn and Sn Zn antisite defects in the surface region of CZTSSe thin films. [ 50 ] As Sn 3 d 5/2 and 3 d 3/2 are a pair of spin split peaks, and Sn 3 d 3/2 is susceptible to interference from the Auger peak of Zn, we only analyze Sn 3 d 5/2 XPS spectra here. As shown in Figure , the binding energy of Sn 3 d 5/2 for the sample W/O can be fitted by two peaks at 486.40 and 485.87 eV, which are assigned to the core levels of Sn 4+ and Sn 2+ , respectively.…”

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

“…Kesterite semiconductors, including Cu 2 ZnSnS 4 (CZTS), Cu 2 ZnSnSe 4 (CZTSe), and Cu 2 ZnSn(S,Se) 4 (CZTSSe), are ideal absorber materials for thin film solar cells due to their earth abundant elemental composition and high theoretical efficiency [ 1–5 ] compared to similarly structured chalcopyrite counterpart Cu(In,Ga)Se 2 (CIGS). However, the power conversion efficiency (PCE) of kesterite solar cells is only 12.6%, [ 6,7 ] far lower than that of CIGS, which has reached 23.35%.…”

Defect‐Resolved Effective Majority Carrier Mobility in Highly Anisotropic Antimony Chalcogenide Thin‐Film Solar Cells

“…These carrier sources are relatively shallow defects, which are fully or partly ionized, providing free carriers at room temperature. Using the admittance analysis methods, [ 13,14 ] the density and activation energy of these defects are extracted (shown in Figure 2c,f and a). Due to the lack of very shallow defects and the negligible intrinsic thermal excitation at room temperature, the free carriers in the QNR mainly come from the partially ionized bulk defects measured by admittance and DLCP.…”