Layered Perovskites in Solar Cells: Structure, Optoelectronic Properties, and Device Design

Abstract

optoelectronic properties akin to industrial juggernauts gallium arsenide and silicon. [1,2] Yet, the materials are compatible with solution-processing techniques such as inkjet printing and spray coating. [3] This unprecedented combination has led to the development of solar cells which already show power conversion efficiencies of over 25%, similar to state-of-the-art poly-Si and other thin-film technologies, in just over 10 years of development. [4] Hybrid perovskites are particularly interesting for indoor applications, with impressive efficiencies of over 35% demonstrated under indoor illumination which may prove a viable option to power the ever expanding Internet of Things. [5] Rather than competing with the current technology giants, perovskites can work together with other solar cell technologies in a tandem configuration. Record efficiencies of over 29% for silicon-perovskite tandem solar cells have already been reported and further progress is expected in the near future. [6] Although perovskite solar cells (PSCs) are on the verge of mass production, two main challenges remain: stability [7] and toxicity. [8] Multiple reviews already address the toxicity concern, and it will not be discussed here. [9][10][11] Layered hybrid perovskites (LPKs) have emerged as an answer to battle stability concerns. Although known for decades, LPKs have only recently been incorporated in photovoltaic (PV) applications, resulting in modest device power conversion efficiencies due to poorer optoelectronic properties. [12][13][14] However, their key advantage is the stabilizing effects of the organic interlayers, which prevents perovskite degradation. [15,16] The organic spacer inhibits ion migration which prevents the formation of irreversible degradation products. [17] Alternatively, LPKs can be deposited over the state-of-the-art perovskite materials to combine the high performance of 3D perovskites with the stabilizing properties of LPKs. [15] Here, the limiting factor is inefficient charge transport across the organic interlayer, currently preventing the full exploitation of the layered structure in PSCs.This can be approached in two ways, either by keeping the LPK layer very thin, currently the most popular approach, or by increasing the electrical conductivity of the material. [18,19] The conductivity can be enhanced through increasing the number of inorganic layers n, but this comes at the price of reduced stability. [20][21][22] The better approach is to enhance the charge transport in LPKs through the molecular engineering of the organic Layered hybrid perovskites (LPKs) have emerged as a viable solution to address perovskite stability concerns and enable their implementation in wide-scale energy harvesting. Yet, although more stable, the performance of devices incorporating LPKs still lags behind that of state-of-the-art, multication perovskite materials. This is typically assigned to their poor charge transport, currently caused by the choice of cations used within the organic layer. On balance, a compromise bet...

Interfacial Engineering by In Situ Building of a 3D/2D Heterojunction for Inverted CsPbI2Br Solar Cells: Beyond Moisture Proof

“…Unlike the 3D perovskite with an interconnected structure, 2D perovskite features a layered structure, in which the extended inorganic networks of [PbX 6 ] 4– octahedrons are separated by bulky organic ammonium cations. − Because of the significant van der Waals interaction between the well-aligned bulky organic cations, the organic layer could exhibit good thermal resistance. Besides, the hydrophobic organic layer can delay or prevent the direct exposure of the inorganic layer to moisture.…”

“…Besides, the hydrophobic organic layer can delay or prevent the direct exposure of the inorganic layer to moisture. Hence, 2D perovskite also displays good moisture stability, which can be further enhanced by reducing the number ( n ) of moisture-sensitive inorganic layers to 1. , To take the advantage of both 2D and 3D perovskites, a variety of 2D/3D hybrid structures have been designed and prepared for PSCs, in which the 2D phase acts as a protective shell against moisture. − Nevertheless, it was found that the layered structure of 2D perovskite is not good for out-of-plane carrier transport. As a result, the 2D/3D structure in regular (n–i–p) PSCs may result in blocked hole transfer from the 3D perovskite absorber to the hole transport layer (HTL).…”

“…As a result, the 2D/3D structure in regular (n–i–p) PSCs may result in blocked hole transfer from the 3D perovskite absorber to the hole transport layer (HTL). To address this issue, many attempts have been made, such as reducing the 2D phase thickness and/or tailoring the organic cation. ,, In addition, very recent studies demonstrate that a well-designed 2D/3D structure could even efficiently promote the hole transfer due to the improved energy level alignment at the perovskite/HTL interface. , Thus, an ideal 2D/3D structure should not only combine the merits of 2D and 3D perovskites but also benefit the carrier transport behavior in PSCs.…”

“…Hence, 2D perovskite also displays good moisture stability, which can be further enhanced by reducing the number (n) of moisture-sensitive inorganic layers to 1. 8,9 To take the advantage of both 2D and 3D perovskites, a variety of 2D/3D hybrid structures have been designed and prepared for PSCs, in which the 2D phase acts as a protective shell against moisture. 10−14 Nevertheless, it was found that the layered structure of 2D perovskite is not good for out-of-plane carrier transport.…”

“…To address this issue, many attempts have been made, such as reducing the 2D phase thickness and/or tailoring the organic cation. 8,15,16 well-designed 2D/3D structure could even efficiently promote the hole transfer due to the improved energy level alignment at the perovskite/HTL interface. 17,18 Thus, an ideal 2D/3D structure should not only combine the merits of 2D and 3D perovskites but also benefit the carrier transport behavior in PSCs.…”