A Review on Emerging Barrier Materials and Encapsulation Strategies for Flexible Perovskite and Organic Photovoltaics

Abstract

Perovskite solar cells (PSCs) and organic photovoltaics (OPVs) have undergone rapid development within the last decade, exhibiting exciting properties such as high efficiency, flexibility, and the potential for large‐scale fabrication through roll‐to‐roll (R2R) processing. Despite this, operational stability is recognized to be an ongoing challenge as prolonged device lifetimes are scarcely observed. This instability can be narrowed down to both “intrinsic degradation” and “extrinsic degradation,” with exposure to moisture and oxygen having detrimental effects on device performance. A means of delaying the degradation of flexible PSC and OPV devices is through barrier encapsulation. Despite glass encapsulation exhibiting ideal barrier properties, the potential for flexible devices and high‐throughput R2R fabrication requires the development of flexible barrier materials and encapsulation strategies. These barriers must demonstrate outstanding moisture permeation resistance, high transparency, chemical and thermal stability, and must be able to withstand repeated mechanical deformation. Herein, the fundamental principles of PSC and OPV devices are initially discussed, highlighting the degradation mechanisms and current stability obstacles. A review of the latest flexible barrier materials and encapsulation strategies follows, introducing stability studies that have been undertaken on flexible PSCs and OPV, along with suggestions as to the direction that future research may take.

Conjugated Polyelectrolyte‐Based Complex Fluids as Aqueous Exciton Transport Networks

“…Major efforts have been undertaken to make new materials for organic photovoltaic devices. [1][2][3][4][5][6][7][8][9] Recently, much work has gone into the use of self-assembly to form components of lightharvesting systems, like electronic energy-transfer antennae. [10][11][12][13][14][15][16][17] Here the self-assembled components are arranged through non-covalent interactions to directionally guide the transport of electronic excited states (excitons), thereby mimicking exciton transport in photosynthetic organisms.…”

Enhanced Thermal Stability of Planar Perovskite Solar Cells Through Triphenylphosphine Interface Passivation

“…[5][6][7][8] In addition, the stability of PSCs falls short of commercially available photovoltaic products, which typically require retention of more than 90 % of their initial performance during the course of their 20-25 year lifetime. [9,10] Various reports have shown PSCs to be unstable even under standard operating conditions with maximum stability testing to date, clocked at only 10000 h. [11,12] The non-ideal performance and low stability are generally attributed to the low formation energy and polycrystalline nature of the perovskite. [13][14][15] These properties imply that a large number of non-stoichiometric defects and dangling bonds are unavoidably generated, particularly for solution-based processing such as spin coating.…”

“…Despite the theoretical limit of 31 %, identified for perovskites with a bandgap of 1.6 eV, the highest PCE achieved for laboratory‐based perovskite solar cells (PSCs) remains distant at 25.5 % [5–8] . In addition, the stability of PSCs falls short of commercially available photovoltaic products, which typically require retention of more than 90 % of their initial performance during the course of their 20–25 year lifetime [9,10] . Various reports have shown PSCs to be unstable even under standard operating conditions with maximum stability testing to date, clocked at only 10000 h [11,12] .…”

Perovskite Photovoltaics for Artificial Light Harvesting

“…Extending the frontiers of photovoltaic technology, artificial light cells (ALCs; i. e., indoor photovoltaics) have recently garnered immense research interest. Research of ALCs has been intently geared towards harvesting and recycling ambient light and thus has possibly enabled efficient energy use in our daily lives [12–17] . Although the spectral intensity, wavelength, and energy harnessed from commonly utilized household light sources are markedly different from those of the Sun (Figure 1a), drawing on this local energy source has become imperative and promising for providing reliable and sustainable off‐grid power supplies in portable and wearable internet of things (IoT) applications, as shown in Figure 1b.…”

“…Research of ALCs has been intently geared towards harvesting and recycling ambient light and thus has possibly enabled efficient energy use in our daily lives. [12][13][14][15][16][17] Although the spectral intensity, wavelength, and energy harnessed from commonly utilized household light sources are markedly different from those of the Sun (Figure 1a), drawing on this local energy source has become imperative and promising for providing reliable and sustainable off-grid power supplies in portable and wearable internet of things (IoT) applications, as shown in Figure 1b. Accordingly, integration of ALCs with several household devices has already been attempted, and as the demand for IoT application power supplies, the ALC market size and revenue are estimated to correspondingly surge.…”