Low‐Dimensional 2‐thiopheneethylammonium Lead Halide Capping Layer Enables Efficient Single‐Junction Methylamine‐Free Wide‐Bandgap and Tandem Perovskite Solar Cells

Abstract

Wide‐bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open‐circuit voltage (VOC) deficit and serious photo‐induced halide segregation remain the main challenges that impede their applications. Herein, a post‐treatment strategy without thermal annealing is presented to form a 2D top layer of 2‐thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing‐free post‐treatment method can more effectively passivate the defects of WBG methylamine (MA)‐free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo‐induced perovskite phase segregation, as compared with the thermal annealing method that yields multi‐2D phases. The resulting opaque and semi‐transparent 1.66 eV‐bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small VOC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA‐free WBG PSCs. Consequently, four‐terminal all‐perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi‐junction tandem solar cells.

Understanding of Defect Passivation Effect on Wide Band Gap p-i-n Perovskite Solar Cell

“…Compared to the P0 absorber, which does not include Pb(SCN) 2 additive, all absorbers including 2 mol % Pb(SCN) 2 exhibit reduced FWHM, indicating an improved grain morphology. Additionally, a peak near ∼5.5°was observed in the lower-angle XRD, originating from the main (002) diffraction peak of the 2D TEA 2 PbX 4 RP phase 16,38 as shown in Figure S2.…”

“…Moreover, the charge distribution is substantially reduced from ∼9.49 × 10 17 cm –3 (P2) to ∼2.71 × 10 17 cm –3 (P2T1) at the edge of the carrier profile ( N CV IF ). The formation of 2D perovskite (TEA 2 PbX 4 ) is reported to shift the Fermi energy level and valence band maximum to downward, thereby creating a hole barrier at the interface (C 60 /2D/3D perovskite). This barrier at the interface effectively inhibits undesired recombination at the C 60 /perovskite interface, ,, and this reduction in recombination is also supported by the 3.5-fold decrease in defects density at the interface ( N CV IF ) of TEACl-treated P2T1 device.…”

Regulating Crystal Orientation via Ligand Anchoring Enables Efficient Wide‐Bandgap Perovskite Solar Cells and Tandems

“…[29] In a separate study, Zhu et al employed an in situ protonation process by adding polyethylenimine family into Cs 0.25 (MA 0.01 FA 0.99 ) 0.75 Pb(I 0.85 Br 0.15 ) 3 perovskite precursors, effectively reducing deep-level traps and enabling 1.65 eV bandgap PSCs with a PCE of 22.33% and a V OC deficit of 0.45 V. [31] In addition to additives, post-treatment strategies have been widely adopted to reduce interface defects and align energy levels between perovskites and charge transport layers. [32][33][34][35][36] For instance, Liu et al reported a grain regrowth and bifacial passivation tactic to minimize nonradiative recombination losses in FA 0.8 Cs 0.15 MA 0.05 Pb(I 0.82 Br 0.18 ) 3 perovskites, yielding a high PCE of 21.90% with a small V OC deficit of 0.43 V. [34] However, it is important to note that most highly efficient WBG PSCs have thus far necessitated the incorporation of volatile methylamine (MA) cation into perovskite films, [30,31,34] which has proven particularly detrimental to the long-term stability of the devices. [32] In addition, significant V OC losses persist, particularly in mixed iodide/bromide systems (E g > 1.63 eV), posing challenges in achieving a V OC deficit lower than 0.40 V compared to their normal-bandgap (1.55 eV) counterparts.…”

“…[32][33][34][35][36] For instance, Liu et al reported a grain regrowth and bifacial passivation tactic to minimize nonradiative recombination losses in FA 0.8 Cs 0.15 MA 0.05 Pb(I 0.82 Br 0.18 ) 3 perovskites, yielding a high PCE of 21.90% with a small V OC deficit of 0.43 V. [34] However, it is important to note that most highly efficient WBG PSCs have thus far necessitated the incorporation of volatile methylamine (MA) cation into perovskite films, [30,31,34] which has proven particularly detrimental to the long-term stability of the devices. [32] In addition, significant V OC losses persist, particularly in mixed iodide/bromide systems (E g > 1.63 eV), posing challenges in achieving a V OC deficit lower than 0.40 V compared to their normal-bandgap (1.55 eV) counterparts. [37] Therefore, it is imperative to explore approaches that further reduce the V OC deficit and mitigate photo-induced halide segregation in MA-free WBG PSCs to bolster device performance and stability.…”