High‐Quality Sequential‐Vapor‐Deposited Cs₂AgBiBr₆ Thin Films for Lead‐Free Perovskite Solar Cells

Abstract

Lead‐free double perovskites have been demonstrated as promising alternatives to solve the toxicity and stability issues in conventional lead trihalide perovskites. However, different solubility of components in the precursors hinders fabrication of double perovskite films with commonly used solution procedures. Here, for the first time, the authors successfully prepared double perovskite Cs2AgBiBr6 thin films throughout a sequential‐vapor‐deposition procedure. The obtained thin films with pure double perovskite phase show large grain sizes, uniform, and smooth surface properties. In addition, the high‐quality vapor‐deposited Cs2AgBiBr6 films exhibit a photoluminescence (PL) lifetime of 117 ns, indicative of significant potential in photovoltaic applications. The resulting solar cells with planar device structure show an optimized power conversion efficiency of 1.37%, which can be maintained at 90% after 240 h of storage under ambient condition. Our results demonstrate the feasibility of employing vapor deposition technique to fabricate high‐quality double perovskite thin films, which paves the way for further development of various optoelectronic devices based on these promising lead‐free semiconductors.

Progress of Lead‐Free Halide Double Perovskites

“…Theoretical studies have shown that the 6s 2 lone-pair states of Pb 2+ ions lead halide perovskites play a critical role in determining their superior optoelectronic properties. [196] Copyright 2018, Wiley-VCH. For halide double perovskites to effectively mimic the optoelectronic properties of their Pb based counterparts, both the B′ site and B″ site cations should possess lone-pair electrons, which can be denoted as ''s 2 +s 2 '' as seen in the hypothetical (MA) 2 TlBiBr 6 .…”

“…For halide double perovskites to effectively mimic the optoelectronic properties of their Pb based counterparts, both the B′ site and B″ site cations should possess lone-pair electrons, which can be denoted as ''s 2 +s 2 '' as seen in the hypothetical (MA) 2 TlBiBr 6 . [78,80,196] Also, Bartesaghi et al reported that the low PCEs (<2.5%) commonly reported for Cs 2 AgBiBr 6 -based PSCs are likely aided by fast carrier recombinations as a result of surface traps at the film surface. As shown in Figure 7a, Ning et al demonstrated the first double perovskite solar cells based on Cs 2 AgBiBr 6 film.…”

“…c) Gao et al, Reproduced with permission. [196] Such physical deposition technique is expected to produce films with impressive morphological features such as large grain sizes, film uniformity, and smooth surface. d) Chen et al, Reproduced with permission.…”

“…e) Wang et al, Reproduced with permission. 2019, 9,1803150 FTO/c-TiO 2 /m-TiO 2 /Cs 2 AgBiBr 6 /PTAA/Au 1.26 - [195] FTO/c-TiO 2 /m-TiO 2 /Cs 2 AgBiBr 6 /SpiroOMeTAD/Au 0.90 - [195] FTO/c-TiO 2 /m-TiO 2 /Cs 2 AgBiBr 6 /PCPDTBT/Au 0.68 - [195] FTO/c-TiO 2 /Cs 2 AgBiBr 6 /P3HT/Au 1.37 - [196] Cs 2 NaBiI 6 FTO/c-TiO 2 /m- www.advancedsciencenews.com stable absorber layers similar to Cs 2 TiBr 6 , the instability seen in CsSnI 3 due to the +2 state of Sn can be eliminated via an oxidative conversion to give Cs 2 SnI 6 with a +4 state Sn. www.advancedsciencenews.com device has been presented by Pantaler et al [195] The origin of this absence of hysteresis is the less trapping/detrapping or ion migration existing in Cs 2 AgBiBr 6 compared with the leadbased hybrid perovskites.…”

Post‐Treatment Engineering of Vacuum‐Deposited Cs2NaBiI6 Double Perovskite Film for Enhanced Photovoltaic Performance

“…To avoid the drawbacks of the solution‐processed double perovskite film, the vacuum deposition technology is a better choice. For example, Liu and co‐workers demonstrated a sequential‐vapor‐deposition procedure to fabricate the Cs 2 AgBiBr 6 film, and a PCE of ≈1.4% can be achieved . The advantages of vacuum deposition technology are 1) facile tenability of film thickness; 2) homogeneous film quality on large‐scale area; and 3) high reproducibility.…”