In kesterite Cu2ZnSn(S, Se)4 (CZTSSe) solar cells, the insufficient CdS/CZTSSe heterojunction built-in electric field due to the low carrier concentration is an important factor limiting the photoelectric conversion performance. Herein, we introduce an extrinsic La3+ incorporation to realize a synergetic carrier doping of this heterojunction. By forming shallow LaCd and LaSn substitution defects, electron and hole concentration in CdS and kesterite has been obviously increased, which effectively improves the electric property and interface charge transfer of the heterojunction. The resulting reduction in the minority carrier loss has finally realized a high cell efficiency of 13.9% at room temperature. Moreover, the carrier doping allows the heterojunction to work in a much wider temperature region and the cell obtains an impressively high efficiency of 22% at 130 K.
The kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have shown a continuous rise in power conversion efficiencies in the past years. However, the encountered interfacial problems with respect to charge recombination and extraction losses at the CdS/CZTSSe heterojunction still hinder their further development. In this work, an additional plasmonic local electric field is imposed into the CdS/CZTSSe interface through the electrostatic assembly of a two-dimensional (2D) ordered Au@SiO2 NP array onto an aminosilane-modified surface absorber. The interfacial electric properties are tuned by controlling the coverage particle distance, and the finite-difference time domain (FDTD) simulation demonstrates that the strong near-field enhancement mainly occurs near the p-n junction interface. It is shown that the imposed local electric field leads to interfacial electrostatic potential (Velec) augmentation and improves the charge extraction and recombination processes. These electric benefits enable remarkable improvements in open-circuit voltage (Voc) and short-circuit current (Jsc), leading to the cell efficiency being increased from 10.19 to 11.50%. This work highlights the dramatic role of the plasmonic local electric field and the use of the 2D Au@SiO2 NP array to modify a surface absorber instead of the extensively used ion passivation, providing a new strategy for p-n junction engineering in kesterite photovoltaics.
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