Designing Effective Hole Transport Layers in Tin Perovskite Solar Cells

Abstract

Beyond collecting hole charge carriers, hole transport layers (HTLs) in perovskite solar cells (PSCs) can play a significant role in determining the perovskite's quality and stability. While diverse prospective HTL materials are explored for high-performance lead-based PSCs, tin-based PSCs predominantly rely on poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) to achieve power conversion efficiency near 15% and around 1 year of N 2 shelf-storage stability. While tin perovskites exhibit distinct characteristics in terms of crystal defect species, interfacial properties, crystallization mechanisms, and shallow energy levels, device architectures and HTL materials are usually adopted from lead PSCs without tailoring them for tin PSCs. In this regard, the effective design of HTLs in tin PSCs remains not well-explored. In this Perspective, we propose a comprehensive set of effective HTL design factors with a dedicated focus on tin PSCs, aiming at upgrading PEDOT:PSS and modifying other prospective HTLs to ultimately break the current performance limit to be competitive with or beyond lead PSCs.

Mixed Self-Assembled Monolayers for High-Photovoltage Tin Perovskite Solar Cells

“…This could pose a challenge in selecting efficient ETL materials. In contrast, an antisolvent-assisted one-step deposition method, which has been commonly used on PEDOT:PSS HTLs, , can avoid this issue and furthermore can be advantageous over forming tin perovskites of high quality, hence being promising for SAM-based TPSCs. Even though one relevant report has been recently published, the reported performance does not exceed that of the two-step method .…”

“…Tin-based perovskite solar cells (TPSCs) are the embodiment of promising next-generation photovoltaics because they hold not only the fundamental merits of lead counterparts, such as high tunability, mechanical flexibility, light weight, and scalability, but also unique merits, including the absence of the toxic element of lead, smaller bandgap (∼1.3–1.5 eV), and decent charge carrier mobility. − High-performance TPSCs (with PCEs approaching 15%) utilize a p-i-n architecture, where poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) is almost universally employed as an HTL. − The polar components exposed at the PEDOT:PSS surfaces can interact strongly via hydrogen bonding with perovskite precursors to promote tin perovskite crystallization and lamination. However, the hygroscopic nature of PEDOT:PSS could induce the formation of interface defects and the degradation of tin perovskites, likely through the breakage of axial Sn–I bonds by H 2 O …”

“…In contrast, a fully covered, uniform tin perovskite film is formed on the SAM with an equimolar ratio of MeO-2PACz to 6PA. Third, to enhance electron transport and increase V oc , we adopt ICBA as an ETL because ICBA can effectively passivate the perovskite top surface against Sn­(IV) defects and is suitable for the uplifted CBM energy levels of the analogous tin perovskites. ,, The so-far developed SAM-based TPSCs use buckminsterfullerenes (namely, C 60 ) as an ETL, − resulting in low V oc (<0.65 V) due to its inefficient surface passivation. Our preliminary results also show the same trend (Figure S2) with the C 60 analogue and ICBA.…”

Stereoselective Polymerization of 3,6-Disubstituted N-Vinylcarbazoles

“…Samples were prepared in THF at 0.1 mg/mL, placed into a 0.1 mm quartz cuvette, and measured using a spectrofluorometer. Interestingly, a minimal difference in excitation–emission spectra was observed between the atactic and isotactic polymers (Figure S72) except for PNVC-Ph, even though the difference in π overlap between stereosequences has been proposed to be critical for fluorescence through excimer formation. , Most derivatives’ excitation falls within the UV, which is important for limiting spectral overlap for perovskite and OPV applications, but their change in fluorescence Stokes shift indicates a significant change in the band structure of these materials (Figure A). Notably, PNVC-Br and PNVC-I display almost no fluorescence due to significant spin–orbit coupling arising from the heavy atom effect leading to phosphorescence. , The rest of the polymer derivatives show a range of behavior.…”