New Insight into Sulfurized and Selenized Kesterite–Titania Nanostructures for CdS-free and HTM-free Photovoltaic and Voltage-Modulated Photodetecting Applications

Abstract

Cu2ZnSnS4 or kesterite and its selenium alloyed counterparts are considered promising for next generation photovoltaic applications due to their excellent optoelectronic properties and earth-abundant, nontoxic composition. In order to alleviate the adverse effects of defects and interfaces on charge separation and transport in current thin film kesterite photovoltaics, new solutions such as the application of an inverted superstrate configuration have been proposed. In this article, sulfurized and selenized kesterite were deposited by solution processing on thin ALD Al2O3 coated TiO2 nanorods to fabricate novel nanostructured devices free of additional buffer layers and hole transfer materials (HTM). The selenized kesterite (CZTSSe) solar cell demonstrated an energy conversion efficiency of 1.85% with high J sc of ∼20 mA/cm2 while the sulfurized kesterite (CZTS) device showed lower solar cell efficiency but excellent photodetecting properties under reverse bias with adjustable working window from visible-only to UV–vis–NIR range.

Overcoming Limitations in Water–Ethanol Sprayed Superstrate Solar Cells by Compositional Engineering of Cu2CdSn(S,Se)4

“…21 Here, a compact or nanostructured thin film of TiO 2 can be adopted as ETL. 22 TiO 2 can act as a stable and protective layer for the FTO while also reducing the risk of shunt paths. However, the growth of CZTS on TiO 2 is challenging; thus, a CdS interlayer is usually necessary, making it hard to control the composition of both the absorber and CdS due to a Cd−Zn exchange during the annealing.…”

Ag‐Refined Kesterite in Superstrate Solar Cell Configuration with 9.7% Power Conversion Efficiency

“…[ 16 ] In addition, it is more convenient to realize the proposed p–i–n design [ 6 ] by referring to other well‐established examples such as the leading‐performing perovskite PVs. [ 17 ] However, with raised challenges in device fabrication and limited research output (<1% of the total publications on kesterite solar cells, source: Web of Science), the technical status of superstrate kesterite devices has long been falling behind its substrate counterparts (Figure S1, Supporting Information), [ 14,18,19 ] having yet to unlock this promising but overlooked research line.…”

Titania as Buffer Layer for Cd-Free Kesterite Solar Cells

“…13 In 2019, again Demopoulos et al, optimized their TiO 2 −NA synthetic procedure reaching efficiencies ∼1% with V oc ∼ 400 mV and J sc ∼ 6.6 mA/cm 2 , always in a sort of superstrate configuration and with an Al 2 O 3 interlayer between CZTS and TiO 2 −NA, converting the architecture to a p-i-n junction. 17 More recently also Wang and co-workers reported an Ag-substituted Se-based kesterite solar cell but always in superstrate configuration, featuring a sputtered layer of TiO 2 with extremely interesting results. 20 In the meantime, other works have been reported employing TiO 2 in CZTS solar cells but interposing a thin layer of CdS between them, thus slightly modifying the band alignment and resulting in efficiencies <1%.…”

“…Demopoulos and co-workers have been pioneers when in 2015 developed a sophisticated but effective synthetic route to grow CZTS nanocrystallites on TiO 2 nanorod arrays (TiO 2 -NA) and used them to produce the first working solar cell (in superstrate configuration, TCO/TiO 2 /interlayer/CZTS-NA/top-contact) showing extremely modest parameters, such as V oc ∼ 180 mV and J sc ∼ 3.3 mA/cm 2 . In 2019, again Demopoulos et al, optimized their TiO 2 –NA synthetic procedure reaching efficiencies ∼1% with V oc ∼ 400 mV and J sc ∼ 6.6 mA/cm 2 , always in a sort of superstrate configuration and with an Al 2 O 3 interlayer between CZTS and TiO 2 –NA, converting the architecture to a p-i-n junction . More recently also Wang and co-workers reported an Ag-substituted Se-based kesterite solar cell but always in superstrate configuration, featuring a sputtered layer of TiO 2 with extremely interesting results .…”

“…Specifically, the CZTS/ZnSnO junction exhibited power conversion efficiencies comparable to those of CZTS/CdS junction . Among the other possibly suitable n-type semiconductors, recent theoretical models indicate TiO 2 as one of the best candidates to be coupled with CZTS. − TiO 2 has been widely employed in dye-sensitized solar cells (DSSC) and perovskite solar cells because of its transparency, transport properties and low-cost precursors, but very little experimental evidence has been recorded of TiO 2 coupled with CIGS or CZTS in a p–n junction. − Calculations of Bencherif and co-workers indicate that a CZTS/TiO 2 junction could lead to a ∼ 5% V oc gain compared to canonical CZTS/CdS, while the simulated optimized solar cell should be able to overcome also the experimental record Fill Factor (FF) values leading to the overall power efficiency of ∼15% . On the other hand, Nisika and co-workers widely studied the properties of the CZTS/amorphous-TiO 2 where a favorable spike-like effect at the p–n junction interface leads to an offset conduction band value of 0.17 eV.…”