Gradient Energy Alignment Engineering for Planar Perovskite Solar Cells with Efficiency Over 23%

Abstract

Organic-inorganic halide perovskite solar cells (PSCs) have a great potential for commercialization owing to their low cost and superior performance. [1] Over the past decade, the power conversion efficiency (PCE) of PSCs has increased from 3.8% [2] to 25.2%, [3] approaching the record efficiency of 26.7% of crystalline silicon solar cells, [4] and becoming one of the most promising candidates for the nextgeneration efficient and low-cost photovoltaic devices. [5] For example, Seok and co-workers introduced additional iodide intoprecursor solutions, resulting in a certified PCE of 22.1%. [6] Recently, Kim et al. investigated the effects of methylammonium chloride (MACl) on the performance of perovskite films and fabricated a device that achieved a certified PCE of 23.5%. [7] It is important to note that all these efficient devices were fabricated with high-temperature-processed TiO 2 mesoporous structures, thus limiting their widespread application. Developing low-temperature-processed electron-transport layer (ETL) [8] for planar structure devices is of great importance. [9] Among them, TiO 2 , [10] SnO 2 , [11] and [6]-phenyl-C 61 -butyric acid methyl ester (PCBM) [12] are the most commonly used ones.The lower efficiency of devices based on planar structures is closely related to insufficient charge extraction [13] and imperfect interfacial band alignment. [14] The insufficient charge extraction between perovskite and ETL can result in charge accumulation, which negatively affects device performance. [15] Therefore, sufficient charge extraction is one of the most important contributors for device efficiency. [16] Recently, researchers have focused on the use of bilayer ETL, [17] and the bilayer stack structure has been demonstrated to be effective for improving device efficiency. As early as 2014, [18] Snaith and co-workers have shown that PSCs with C 60 -modified TiO 2 can significantly enhance electron transfer and result in a largely improved performance of 17.3% and a decrease in hysteretic behavior. Petrozza and co-workers demonstrated that insufficient charge extraction from the perovskite film to the ETL can be remedied using a TiO 2 /PCBM bilayer ETL, and a PCE of 17.9% was achieved. [19] Recently, Choi and co-workers achieved a PCE of 21.1% using SnO 2 @TiO 2 ETL, [20] and Kong and co-workers showed a PCE of 21.4% using the same type of ETL. [21] Numerous other efforts have been undertaken to enhance the performance of PSCs with bilayer ETLs, such as SnO 2 @TiO 2 , [22] SnO 2 /PCBM, [23] An electron-transport layer (ETL) with appropriate energy alignment and enhanced charge transfer is critical for perovskite solar cells (PSCs). However, interfacial energy level mismatch limits the electrical performance of PSCs, particularly the open-circuit voltage (V OC ). Herein, a simple low-temperature-processed In 2 O 3 /SnO 2 bilayer ETL is developed and used for fabricating a new PSC device. The presence of In 2 O 3 results in uniform, compact, and low-trap-density perovskite films. Moreover, the conduction...

TiO2 Colloid‐Spray Coated Electron‐Transporting Layers for Efficient Perovskite Solar Cells

“…[2,3] PSCs with an n-i-p structure normally comprise a stack of transparent conductive oxide (TCO)/electron-transporting layer (ETL)/perovskite/hole-transporting layer (HTL)/counter electrode. Besides, recent wide and extensive research on perovskites [4,5] and HTL materials, various ETL materials have also been explored: [6][7][8] The most attractive of them would be TiO 2 . Owing to its advantages (e.g., good transparency, favorable bandgap edge positions in relation to perovskites, environmental stability, and the feasibility of the solution processing with low-fabrication costs), TiO 2 has been widely adopted for the fabrication of high-efficiency PSCs.…”

A Review on Solution‐Processable Dopant‐Free Small Molecules as Hole‐Transporting Materials for Efficient Perovskite Solar Cells

“…Due to the lack of electron-transporting scaffold to collect these photogenerated electrons deep inside the perovskite, which is previously provided by the mesoporous layer, the dense ETL in planar n-i-p structure is often required to be of high conductivity, and is typically made of tin oxides that are more conductive than titanium oxides. [8][9][10][11] The third one is inverted p-i-n type, where the locations of ETL and HTL are opposite to that for planar n-i-p device. In the regular devices (including mesoporous and planar n-i-p ones), photogenerated holes come out near the interface of ETL/perovskite, thus a longer diffusion distance is necessary for them before reaching the interface of perovskite/HTL where they are collected by the HTL.…”

Development of a Perovskite Solar Cell Architecture for Opaque Substrates

“…[ 1 ] Driven by the promise of even higher efficiencies, longer lifetimes, low costs, and numerous high‐throughput deposition techniques, PSC technology is expected to emerge in commercial applications in the near future. [ 2–8 ] Products with PSCs will likely first enter in markets where additional features, next to efficiency and lifetime, are relevant. The most common examples of such characteristics are aesthetics, flexibility, low mass, and high low‐light intensity efficiency.…”