Improvement of Photovoltaic Performance of Cu₂ZnSn(S,Se)₄ Solar Cells by Modification of Back Electrode Interface with Amorphous Boron Nitride

Abstract

band gap (E g = 1.0-1.5 eV). [1][2][3][4] Currently, the highest certified power conversion efficiency (PCE) of 13% was obtained for CZTSSe-based thin film solar cell by Xin et al., [5] demonstrating its substantial commercial prospect. While it is still much lower than PCE of the counterpart CIGS devices (23.5%) [6] and its Shockley-Queisser limit (32.8%). [7] There are two main reasons for this. One of the reasons limiting PCE improvement is the complicated defects and defect clusters in CZTSSe, such as Cu Zn , Sn Zn , and 2Cu Zn +Sn Zn , which is resulting from the similar ionic radii and coordination environments of Cu + , Zn 2+ , and Sn 4+ . [8] The presence of harmful deep energy level defects and defect clusters at the bulk of CZTSSe and CZTSSe/CdS interface, resulting in a short minority carrier lifetime and significant band tailing, and hence, a large V OC deficit and low efficiency. In recent years, the most prevalent method to mitigate the defects is equivalent cation substitution, such as Ag substitution for Cu, Cd substitution for Zn, etc. [9,10] Another limitation of PCE is the unfavorable back electrode interface. [11] According to thermodynamic calculations, the Mo/ CZTSSe interface is not as chemically stable as Mo/CIGS interface and the decomposition reaction between CZTSSe absorber and Mo back electrode is inevitable during selenization process, as shown in Equation (1). [12] Thus, the undesired secondary phases are produced at the Mo/CZTSSe back interface, not only damaging the absorber quality but also aggravating the back interface recombination. Meanwhile, the voids would occur at the Mo/ CZTSSe back interface during the decomposition reaction owing to the volatilization of Sn(S,Se) and the diffusion of Cu. The shunt paths caused by these voids reduce the effective volume of the absorber and block the transportation of carrier. [13,14] In addition, it is worth noting that the Mo(S,Se) 2 can form through both the Equations (1) and (2) during selenization process [12,15]

Methods for Preparation of Hexagonal Boron Nitride Nanomaterials

“…Furthermore, its exceptional mechanical strength and flexibility render it a prime material for flexible electronics . Atomically thin 2D h -BN nanostructures can serve as transparent conducting electrodes in applications such as solar cells and touchscreens . For a more comprehensive review of h -BN nanomaterials in photonics and electronics, please refer to the work of Kim et al…”

2D Ti3C2-MXene Serving as Intermediate Layer between Absorber and Back Contact for Efficient CZTSSe Solar Cells

“…Thus, much attention has been paid to the CZTSSe/Mo interface to suppress the CZTSSe decomposition and Mo­(S,Se) 2 expansion. In order to suppress Mo­(S,Se) 2 formation as well as improve the back interface quality, various intermediate layers, including metals, , metal oxides, − metal chalcogenides, metal nitride, − carbon materials, − and other nonorganic materials, − had been introduced between the CZTSSe absorber and Mo back. However, the disadvantages of these intermediate layers cannot be ignored.…”

Improvement of Performance of Cu2ZnSn(S, Se)4 Solar Cells by Low‐Temperature Annealing of B‐Doped CdS

“…[25] The back interfacial recombination is reduced by inserting the buffer layer between Mo and CZTSSe or field passivation. [26][27][28] Although a great program in improvement of V oc and FF has been achieved by these approaches, the PCE is still much smaller than that of CIGS solar cells, and further research work is still needed.…”