Double‐Sided Surface Passivation of 3D Perovskite Film for High‐Efficiency Mixed‐Dimensional Perovskite Solar Cells

Abstract

Defect‐mediated carrier recombination at the interfaces between perovskite and neighboring charge transport layers limits the efficiency of most state‐of‐the‐art perovskite solar cells. Passivation of interfacial defects is thus essential for attaining cell efficiencies close to the theoretical limit. In this work, a novel double‐sided passivation of 3D perovskite films is demonstrated with thin surface layers of bulky organic cation–based halide compound forming 2D layered perovskite. Highly efficient (22.77%) mixed‐dimensional perovskite devices with a remarkable open‐circuit voltage of 1.2 V are reported for a perovskite film having an optical bandgap of ≈1.6 eV. Using a combination of experimental and numerical analyses, it is shown that the double‐sided surface layers provide effective defect passivation at both the electron and hole transport layer interfaces, suppressing surface recombination on both sides of the active layer. Despite the semi‐insulating nature of the passivation layers, an increase in the fill factor of optimized cells is observed. The efficient carrier extraction is explained by incomplete surface coverage of the 2D perovskite layer, allowing charge transport through localized unpassivated regions, similar to tunnel‐oxide passivation layers used in silicon photovoltaics. Optimization of the defect passivation properties of these films has the potential to further increase cell efficiencies.

2D/3D Heterostructure for Semitransparent Perovskite Solar Cells with Engineered Bandgap Enables Efficiencies Exceeding 25% in Four‐Terminal Tandems with Silicon and CIGS

“…We mainly attribute this enhancement to reduced non‐radiative recombination losses by formation of a 2D‐RP interlayer, which passivates the surface of the 3D double‐cation perovskite layer. [ 94,99,101 ] Furthermore, the widening of the bandgap at the film surface due to the 2D material with a wider bandgap might lead to a better energetic alignment with the charge transport layer and hence reduced interfacial recombination, [ 87 ] as proposed by several recent studies. [ 83,92,100–103 ] However, a detailed experimental analysis of all these factors is beyond the scope of the current work.…”

“…[ 79,86,87 ] One popular approach to reduce the V OC deficit is to deposit a large organic cation on the surface of a 3D perovskite film, which acts as a 2D passivation agent and/or improves the energetic alignment with the charge transport layer. [ 92–100 ] In this regard, we have recently developed a novel 2D/3D perovskite heterostructure fabricated by spin‐coating n ‐butylammonium bromide (BABr) on top of a wide‐bandgap double‐cation perovskite absorber with E g ≈ 1.74 eV (FA 0.83 Cs 0.17 Pb(I 0.6 Br 0.4 ) 3 ), resulting in a record V OC of up to 1.31 V for this bandgap and an improved stabilized PCE of up to 19.4%. [ 101 ]…”

3D/2D Bilayerd Perovskite Solar Cells with an Enhanced Stability and Performance

“…Organic salt, composed of bulky organic cations and counter halide (see Section 4 . Organic salt for 2D perovskite for details), is dissolved in isopropyl alcohol (IPA) [ 24 , 25 , 26 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ] or chlorobenzene (CB) [ 36 , 42 ] and dripped on the surface of a spinning 3D perovskite film, whose excess PbI 2 readily reacts with the organic salt, leading to the formation of a 2D capping layer on the surface during the post annealing process ( Figure 2 a). Alternatively, an immersion of the 3D perovskite film in the IPA solution containing the organic salt for 2D can be adopted, instead of dripping the solution, in order to induce the 2D capping layer ( Figure 2 b) [ 25 ].…”

“…The exposed Pb-I framework is reacted with 5-aminovaleric acid iodide (AVAI), resulting in (AVA) 2 PbI 4 with an improved interface [ 26 ]. The in-situ growth method for the 2D capping layer can be further extended to form double 2D passivation layers on the top and bottom of the 3D perovskite film [ 41 ].…”

“…The growth of a 2D layer on the surface of a 3D film not only passivates the defect by acting as an ion scavenger during the formation of the capping layer [ 35 ], but also inhibits the ions from migrating toward the adjacent layers during the device operation [ 36 , 44 ]. The suppressed charge recombination is frequently monitored by an increased PL intensity, with a prolonged carrier life time in the presence of the 2D capping layer compared to the pristine 3D film [ 25 , 26 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 36 , 37 , 39 , 40 , 41 , 45 ]. The PL intensity corresponding to the 3D perovskite film was considerably enhanced by post-treatment with n-BAI [ 41 ].…”