Compositional Control in 2D Perovskites with Alternating Cations in the Interlayer Space for Photovoltaics with Efficiency over 18%

Abstract

light-emitting diodes, [5][6][7] and photodetectors, [8,9] because of their remarkable structural flexibility, tunability, and excellent stability compared with their 3D perovskite counterparts. [10][11][12] 2D perovskites are generally a class of quantum wells (QWs), including Ruddlesden-Popper (RP), [13][14][15] Dion-Jacobson (DJ), [16][17][18] and alternating cations in the interlayer space (ACI) perovskites. [19,20] The RP and DJ families adopt the general formulas A′ 2 A n−1 M n X 3n+1 and BA n−1 M n X 3n+1 , respectively, where A is a univalent organic cation: methylammonium (MA + ) or formamidinium (FA + ), A′ is a large univalent organic spacer cation like phenylethylammonium (PEA + ), [8,21] or butylammonium (BA + ), etc., [3,22] B is a divalent organic cation like 3-(aminomethyl)piperidinium (3AMP 2+ ) [10] or 1,3-propanediamine. [23] Much work on 2D perovskites to date has focused on the RP and DJ families. For example, it was found that the incorporation of large organic spacer cations leads to the formation of a QW structure with strong quantum confinement, which leads to a higher bandgap and large exciton binding energy. [14,[24][25][26][27] The RP and DJ perovskites feature poor charge dissociation and transportation within the bulk polycrystalline film, which significantly limits the power conversion efficiency (PCE) of solar cells. [28][29][30] To address the issue, a hot-casting strategy was developed to achieve preferential outof-plane alignment of RP QWs. [3] A systematic understanding of how RP perovskites are formed as well as the charge transfer between QWs were also demonstrated, which guided development of the dynamic control of the phase transformation during QWs growth for better compositional and orientation control. [31][32][33][34][35][36] Compositional and solvent engineering were also developed to fabricate high-quality DJ films with significantly improved charge transport. [23,37] For the RP and DJ families, much has been achieved toward a deep understanding of the relationships between molecular chemistry, crystal structure, film quality and optoelectronic properties, leading to outstanding PCEs of 15.42% and 13.3% for PR and DJ perovskite solar cells, respectively. [23,38] The hybrid halide ACI perovskites, which are derived from the oxide perovskite family, are a very new entry in the class 2D perovskites stabilized by alternating cations in the interlayer space (ACI) represent a very new entry as highly efficient semiconductors for solar cells approaching 15% power conversion efficiency (PCE). However, further improvements will require understanding of the nature of the films, e.g., the thickness distribution and charge-transfer characteristics of ACI quantum wells (QWs), which are currently unknown. Here, efficient control of the film quality of ACI 2D perovskite (GA)(MA) n Pb n I 3n+1 (〈n〉 = 3) QWs via incorporation of methylammonium chloride as an additive is demonstrated. The morphological and optoelectronic characterizations unambiguously demonstrate that the additive ena...

Crystallization Kinetics in 2D Perovskite Solar Cells

“…[58] The alternating arrangement of guanidine (GA + ) and MA + (or FA + ) between the organic layers can form another ACI 2D perovskite with high crystal symmetry and lower bandgap. [151][152][153] In 2017, Kanatzidis and co-workers reported an ACI based 2D perovskite for the first time (Figure 8b). [67] The GAMA 3 Pb 3 I 13 has the smallest optical gap in the series, E g = 1.73 eV, making it a good candidate for a light-absorbing material in solar cells.…”

Water‐Assisted Crystal Growth in Quasi‐2D Perovskites with Enhanced Charge Transport and Photovoltaic Performance

“…[ 11,12 ] As a result, charge transport and extraction are hindered in quasi‐2D PSCs. To date, the highest reported PCEs of quasi‐2D PSCs ( n ≤ 5) remain around 18%, [ 13–15 ] showing considerable performance gaps with regard to 3D‐PSCs.…”

“…The difference in the evolution of TA signals assigned to the different bands reveals the scenario of charge transfers which tend to from higher energy phases (corresponding to smaller n ‐values) to low energy 3D phase ( n ≈ ∞), leading to the populating charges at the 3D components and increased TA signals. [ 13,35,40 ] Through fitting the rising part of the TA dynamics probed at n ≈ ∞ phase, we identified a shorter carrier populating time (25.1 ps) in the water‐processed film, compared to a population time of 44.3 ps in the control film. The results point to that charge transfers (most likely the electrons in our case) from the smaller‐ n phases to n ≈ ∞ phase may occur more efficiently in the perovskite film processed with the water‐containing precursors, which is a key attribute to the enhancements of J sc and PCE in the solar cells.…”

Multi-component engineering to enable long-term operational stability of perovskite solar cells

“…Due to tolerance factors, the use of a large bulkier organic cation results in the transformation of the 3D perovskites into the 2D layered perovskite structure, which is environmentally more stable [60,61]. Although more efforts to enhance device efficiency are required [62], the adoption of 2D/3D hybrid structures or 2D interlayers is promising routes to explore the advantages of both types of perovskites. For instance, hybrid 2D/3D PSCs have achieved the longest reported operational stability, currently at 10 000 h (around 1 year), by introducing the 5-AVAI molecule within the halide perovskite absorber [2].…”