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A cation substitution in Cu2ZnSn(S,Se)4(CZTSSe) offers a viable strategy to reduce the open-circuit voltage (Voc)-deficit by altering the characteristics of band-tail states, antisite defects, and related defect clusters. Herein, we report a facile single process, i.e., simply introducing a thin Ag layer on a metallic precursor, to effectively improve the device characteristics and performances in kesterite (Agx,Cu1–x)2ZnSn(Sy,Se1–y)4(ACZTSSe) solar cells. Probing into the relationship between the external quantum efficiency derivative (dEQE/dλ) and device performances revealed the Voc-deficit characteristics in the ACZTSSe solar cells as a function of Cu and Ag contents. The fabricated champion ACZTSSe solar cell device showed an efficiency of 12.07% and a record low Voc-deficit of 561 mV. Thorough investigations into the mechanism underpinning the improved performance in the ACZTSSe device further revealed the improved band-tailing characteristic, effective minority carrier lifetime, and diode factors as well as reduced antisite defects and related defect clusters as compared to the CZTSSe device. This study demonstrates the feasibility of effectively suppressing antisite defects, related defect clusters, and band-tailing characteristics by simply introducing a thin Ag layer on a metallic precursor in the kesterite solar cells, which in turn effectively reduces the Voc-deficit.

An electron transport layer is essential for effective operation of planar perovskite solar cells. In this Article, PW12–TiO2composite was used as the electron transport layer for the planar perovskite solar cell in the device structure of fluorine-doped tin oxide (FTO)-glass/PW12–TiO2/perovskite/spiro-OMeTAD/Au. A proper downward shift of the conduction band minimum (CBM) enhanced electron extraction from the perovskite layer to the PW12–TiO2composite layer. Consequently, the common hysteresis effect in TiO2-based planar perovskite solar cells was significantly reduced and the open circuit voltage was greatly increased to about 1.1 V. Perovskite solar cells using the PW12–TiO2compact layer showed an efficiency of 15.45%. This work can contribute to the studies on the electron transport layer and interface engineering for the further development of perovskite solar cells.

Back contact modification plays an important role in improving energy conversion efficiency of Cu2ZnSnS4(CZTS) thin film solar cells. In this paper, an ultrathin carbon layer is introduced on molybdenum (Mo)-coated soda lime glass (SLG) prior to the deposition of CZTS precursor to improve the back contact and therefore enhance CZTS solar cell efficiency. By introducing this layer, the short circuit current (Jsc) and device conversion efficiency increase for both nonvacuum (sol–gel) and vacuum (sputtering) methods. Specifically, for the sol–gel based process, Jscincreases from 13.60 to 16.96 mA/cm2and efficiency from 4.47% to 5.52%, while for the sputtering based process, Jscincreases from 17.50 to 20.50 mA/cm2and efficiency from 4.10% to 5.20%. Furthermore, introduction of this layer does not lead to any deterioration of either open circuit voltage (Voc) or fill factor (FF).

A facile sol–gel and selenization process has been demonstrated to fabricate high-quality single-phase earth abundant kesterite Cu2ZnSn(S,Se)4(CZTSSe) photovoltaic absorbers. The structure and band gap of the fabricated CZTSSe can be readily tuned by varying the [S]/([S] + [Se]) ratios via selenization condition control. The effects of [S]/([S] + [Se]) ratio on device performance have been presented. The best device shows 8.25% total area efficiency without antireflection coating. Low fill factor is the main limitation for the current device efficiency compared to record efficiency device due to high series resistance and interface recombination. By improving film uniformity, eliminating voids, and reducing the Mo(S,Se)2interfacial layer, a further boost of the device efficiency is expected, enabling the proposed process for fabricating one of the most promising candidates for kesterite solar cells.