High‐Performance Flexible Perovskite Solar Cells Enabled by Low‐Temperature ALD‐Assisted Surface Passivation

Abstract

In addition to the extremely high efficiency, mechanical flexibility and solution processability of perovskite materials offer the great potential towards large-scale roll-to-roll manufacturing of PeSCs. [9][10][11][12][13] To achieve high-performance flexible PeSCs, three key issues must be addressed: 1) new flexible transparent electrode (FTE) solutions to replace the brittle indium-tin-oxide (ITO) or fluorine-doped tin-oxide (FTO) electrode, 2) low-temperature processing of all functional layers to match the thermal limit of plastic substrates, and 3) interface engineering to minimize the charge recombination loss.Undoubtedly, ITO or FTO is the most commonly used transparent conductor due to its excellent electrical conductivity (with a sheet resistance of 10-20 Ω sq −1 ) and optical transparency (with a transmittance of 85-90% over the visible wavelength region). [14] However, its role in flexible optoelectronic devices is limited due to the inherent shortcomings of brittleness, material scarcity, as well as high-temperature and low-throughput deposition process. [15,16] To date, several FTEs such as graphene, [17] metal grids, [18] and silver nanowires (AgNWs) [19] have been exploited to replace ITO and FTO, since they show extraordinary electrical, optical, and mechanical properties. Especially, AgNWs-based random network is solution processable and cost effective, making it one of the most promising candidates for alternative FTEs in flexible PeSCs. [20][21][22] Regardless of a strong potential to replace ITO, several obstacles should be overcome for AgNWs-based FTEs. First, the randomly distributed AgNWs during the solution process result in high surface roughness, which may cause the electrical short-circuits in the overlapped perovskite films due to the protuberant nodes of AgNWs. [20,21] Second, AgNWs suffer from the chemical reaction when they are in direct contact with halide perovskite films, which would severely restrict the device performance. [22,23] Third, the electrical failure and instability of AgNWs may occur due to Joule heating at the junctions of nanowires. [24,25] To solve the aforementioned issues, a feasible solution is to insert a buffer layer between AgNWs and perovskite films to reduce surface roughness and improve the electrical stability of AgNWs-based FTEs. The buffer layer should be sufficiently transparent and conductive without sacrificing the optical Flexible perovskite solar cells (PeSCs) hold great potential as a leading technology for large-scale roll-to-roll production of highly efficient renewable energy sources. To achieve long-term bendability and competitive photovoltaic properties for flexible PeSCs, an efficient strategy is reported for a fully indium-free flexible composite electrode, consisting of solution-processed silver nanowires (AgNWs) conductive network, a sol-gel-derived ZnO protective layer for smoothing the surface, and an atomic-layer-deposited TiO 2 passivation layer for eliminating the perovskite decomposition. The synergetic interplay of this electrod...

Application of ultrathin TiO2 layers in solar energy conversion devices

“…128 Because of the instability against high temperature of plastic substrate, a lot of efforts are focused on developing low-temperature processing of the functional layers, including TiO 2 ETL, in the plastic-based flexible perovskite solar cell. [129][130][131][132] For example, Jeong et al developed ultraviolet (UV)-assisted solution process to fabricate uniform and compact Nb-doped TiO 2 ETL at temperature lower than 50°C. The UV curing induced the removal of the organic ligands in the Ti-precursor.…”

FAPbI3 Flexible Solar Cells with a Record Efficiency of 19.38% Fabricated in Air via Ligand and Additive Synergetic Process

“…Many efforts have been focused on the flexible PSCs (FPSCs) . The highest PCE of 18.40% for FPSCs based on CH 3 NH 3 PbI 3 (MAPbI 3 ) was achieved by Liu and co‐workers .…”

Incorporating a Polar Molecule to Passivate Defects for Perovskite Solar Cells

“…Lead halide perovskites with strong optical absorption and high carrier mobility have attracted extensive research interest as an excellent light absorber in perovskite solar cells (PSCs) . Although the defects at the film surface and grain boundaries of the perovskite layer inevitably lead to charge recombination and efficiency loss, a lot of effort has been devoted to defect passivation of the perovskite layer, achieving efficiency enhancement .…”