Surface Passivation Using 2D Perovskites toward Efficient and Stable Perovskite Solar Cells

Abstract

first solid-state perovskite solar cell (PSC) was successfully prepared by introducing Sprio as a hole transport layer (HTL), tremendous efforts have been devoted to further promoting the photovoltaic performance, including surface passivation, bulk doping, processing engineering, and optimizing the structure of the device. [9][10][11][12][13][14][15][16][17][18][19][20][21] Consequently, the power conversion efficiency (PCE) of PSCs has dramatically increased from the initial 9% to an impressive 25.2% in several years. [22,23] To date, the coexistence of high efficiency and long-term stability has become a crucial requirement for successful PSC applications. 2D perovskites (consisting of pure 2D and quasi-2D perovskites) have emerged as a new family of photovoltaic materials that have been proven to resolve the problem of instability in perovskites. Owing to the insulating spacer layer, inherent outstanding long-term stability is obtained in 2D perovskites, including hydrophobicity, suppression of ion migration, and larger formation energy. [24][25][26][27][28] However, severe carrier recombination occurs due to the combined effect of quantum confinement and dielectric confinement, rooted in the natural multiple quantum wells structure (MQWs) (Figure 1), where the inorganic parts act as potential "wells" while the organic parts act as "walls", which shows a boost in the photovoltaic performance of 2D PSCs. [29][30][31] To realize the coexistence of high efficiency and ultrastability in PSCs, researchers began to construct 2D/3D heterostructures by surface passivation. [32][33][34][35][36][37][38][39][40] In fact, before the boosting of the 2D/3D stacking concept, many researchers have applied large ammonium cations (such as phenethylamine (PEA), butylamine (BA), and quaternary ammonium (QA)) as defect passivants to 3D perovskite solar cells. [41][42][43][44][45] During this period, the pure PEA-or BA-based 2D perovskites have been explored as light-absorbing materials for better stability. [25,46] In 2015, Yao et al. introduced in situ grown 2D perovskite (PEI) 2 PbI 4 (PEI: polymeric ammonium) on an MAPbI 3 film, leading to more stable and efficient PSCs. [47] In 2016, discussions and analyses of the surface passivation effect began to emerge, which involved exploring a series of 2D perovskite molecules (such as aniline, benzylamine, and PEA). [42,45,48] The concept of 2D/3D stacking really stood out in 2018 by unveiling the chemical reaction mechanism for heterojunction formation and the mechanism for enhancing stability. For example, Huang 3D perovskite solar cells (PSCs) have shown great promise for use in next-generation photovoltaic devices. However, some challenges need to be addressed before their commercial production, such as enormous defects formed on the surface, which result in severe SRH recombination, and inadequate material interplay between the composition, leading to thermal-, moisture-, and light-induced degradation. 2D perovskites, in which the organic layer functions as a protective barrier ...

Improvement in the Performance of Inverted 3D/2D Perovskite Solar Cells by Ambient Exposure

“…[45] This decrease likely occurs due to insulating nature of PEAI [21] and/or worsening of the charge collection at the top interface with ETL. [21,45] In inverted solar cells, PEAI has been proposed to be used for the modification of the bottom rather than the top interface, [45][46][47] although there have been reports where the PEA-based treatment of the top surface resulted in improved device performance. [29,49] For devices based on ambient exposed PEAI-treated perovskite, J sc increased to %20.6 mA cm À2 after 15 min exposure and reached its maximum around 22 mA cm À2 after 45 min exposure, while V oc and FF also increased.…”

“…[ 45 ] This decrease likely occurs due to insulating nature of PEAI [ 21 ] and/or worsening of the charge collection at the top interface with ETL. [ 21,45 ] In inverted solar cells, PEAI has been proposed to be used for the modification of the bottom rather than the top interface, [ 45–47 ] although there have been reports where the PEA‐based treatment of the top surface resulted in improved device performance. [ 29,49 ]…”

“…Perovskite solar cells (PSCs) have attracted increased attention in recent years due to their high efficiency. [ 1–50 ] However, various instabilities under normal operating conditions (exposure to ambient air/moisture, illumination, elevated temperature, etc.) have been hindering the efforts in PSC commercialization.…”

“…[ 4 ] Different bulky organic cations have been reported for this purpose, [ 2–4,14,15,43 ] but phenethylammonium (PEA) remains among the most commonly used spacer cations for 3D/2D and quasi‐2D perovskite films. [ 2–10,16–24,39,40,44–47,49 ] Its use has been demonstrated to improve stability of MA‐based, [ 3 ] formamidinium (FA)‐based, [ 2,4,7 ] and Cs‐based perovskites, [ 40 ] as well as mixed composition perovskites. [ 4,5,8–10 ] In addition, it has been used as an additive to the perovskite to produce varying amounts and different 2D/quasi‐2D phases, [ 7,16,18,23,40 ] and to modify perovskite interfaces with electrode, [ 9 ] top hole transport layer (HTL), [ 5,6,8,10,44 ] bottom HTL, [ 20,39,45,49 ] top electron transport layer (ETL), [ 21,22,29,45,49 ] and both perovskite/charge transport layer interfaces.…”

Phase‐Pure Engineering for Efficient and Stable Formamidinium‐Based Perovskite Solar Cells

“…[7,8] OILHPs have a generic chemical formula of ABX 3 , where the monovalent A-site cation is methylammonium (MA), formamidinium (FA), or cesium ion (Cs) in the cubo-octahedral site, B-site divalent metal cation is lead (Pb), and X-site anion is a halide (e.g., iodide (I), bromide (Br), and/or chloride (Cl)). [9][10][11][12] Up to now, the most commonly reported OILHPs are based on CH 3 NH 3 PbI 3 (MAPbI 3 ) and the PCEs of these devices have quickly reached over 20%. [13,14] However, MAPbI 3 was found to undergo reversible phase transition from tetragonal to cubic phase at 55 C that is in the range of the solar cell operating temperature, resulting in the undesirable degradation of photovoltaic performance.…”