Atomic Layer Engineering of Aluminum‐Doped Zinc Oxide Films for Efficient and Stable Perovskite Solar Cells

Abstract

promising light absorber materials, demon strating low-cost solution processing, ease of fabrication, and outstanding optoelectronic properties. [1,2] Since the first report on the perovskite solar cells (PSCs) employing methylammonium lead iodide (MAPbI 3 ), [3] their power conversion efficiency (PCE) has now exceeded 25% for small-area cells. [4,5] The high efficiency of PSCs is achieved by tuning the perovskite layer through compositional engineering, [6][7][8] surface passivation, [9][10][11][12][13] and/or by using various additives. [14][15][16] Besides component engineering of the perovskite layer, a lot of works have been devoted to the development of efficient charge transport layers. [17][18][19][20][21] Particularly, the electron transport layers (ETLs) play an important role in realizing efficient and stable PSCs. [22,23] Thus far, titanium dioxide (TiO 2 ) is a widely applied ETL in PSCs but it suffers from low conductivity and high surface defect density. [24] Among alternative ETLs, zinc oxide (ZnO) has been regarded as a convenient candidate due to its high electron mobility and well-matched energy level with perovskite material. [25,26] This Atomic layer deposition (ALD) has been considered as an efficient method to deposit high quality and uniform thin films of various electron transport materials for perovskite solar cells (PSCs). Here, the effect of deposition sequence in the ALD process of aluminum-doped zinc oxide (AZO) films on the performance and stability of PSCs is investigated. Particularly, the surface of AZO film is terminated by diethylzinc (DEZ)/H 2 O (AZO-1) or trimethylaluminum (TMA)/H 2 O pulse (AZO-2), and investigated with surface-sensitive X-ray photoelectron spectroscopy technique. It is observed that AZO-2 significantly enhances the thermal stability of the upcoming methylammonium lead iodide (MAPbI 3 ) layer and facilitates charge transport at the interface as evidenced by photoluminescence spectroscopes and favorable interfacial band alignment. Finally, planar-type PSC with AZO-2 layer exhibits a champion power conversion efficiency of 18.09% with negligible hysteresis and retains 82% of the initial efficiency after aging for 100 h under ambient conditions (relative humidity 40 ± 5%). These results highlight the importance of atomic layer engineering for developing efficient and stable PSCs.

Key Factors Affecting the Stability of CsPbI3 Perovskite Quantum Dot Solar Cells: A Comprehensive Review

“…conducted a study on the characteristics of ETL and device stability by controlling the termination of the AZO layer. [ 142 ] Consequently, the perovskite solar cells with a controlled ALD–AZO layer showed better moisture stability than ZnO‐based perovskite solar cells, which maintained more than 80% of initial efficiency after 100 h under 40% relative humidity without encapsulation. Although the ALD technique has not yet been applied in the PQD solar cell field, it has been used in other optoelectronic devices, such as LEDs.…”

Recent Criterion on Stability Enhancement of Perovskite Solar Cells

“…However, it was later corroborated by researchers that the hysteresis index of a solar cell somehow originates from its intrinsic properties, rather than the scan rates or direction of the applied bias. Amongst them, the ferroelectric and large dielectric properties of perovskite sensitizers at the nano-scale [34,134], the interfacial ferroelectric characteristics of the device [18], ion migration [35,36], mismatched energy band alignment of the device layers [38,39], slower trapping-detrapping of charges at the grain boundaries or the barriers of different layers [40,135], inefficient charge transportation or extraction by ETLs and HTLs [42,43], imbalance in the charge transport through HTLs and ETLs [44,45], various structural or chemical changes of the involved materials (e.g., perovskite absorber, ETL, and HTL) during operation or in response to various hostile environmental parameters such as temperature and humidity [134,136], undesirable charge trapping at the defect sites of different layers of the device created by such deteriorations [137,138], etc., are attributed to such anomalous PSC device behavior. Some researchers even mentioned it as a light-induced hysteresis in solar cell devices [35,129,139].…”

“…The reason behind such PV behavior is still unknown. However, researchers have attributed several factors to it, such as the large dielectric properties of perovskite sensitizers at the nano-scale [33,34], interfacial ferroelectric characteristics of the device [15], ion-migration [35][36][37], mismatched energy band alignment of the device layers [38,39], the slower trapping-detrapping of charges at the grain boundaries or the barriers of different layers [40,41], inefficient charge transportation or extraction by ETLs and HTLs [42,43], and imbalance in the charge transport through HTLs and ETLs [44,45], etc.…”

Organic Ligand‐Free ZnO Quantum Dots for Efficient and Stable Perovskite Solar Cells

“…[5,[42][43][44][45][46][47][48][49] Remarkably, the state-of-the-art PCE (22.6%) among reported low-temperature processed PSCs was achieved for a device based on a sol-gel-derived ZnO layer modified by potassium chloride. [36] On the other hand, to avoid the participation of organic ligand in the synthetic process and/ or negligible organic impurities in the resulting ZnO films, alternative strategies for ZnO film growth by an atomic layer deposition (Table S1, entry 22, Supporting Information), [50] and a solution-processed combustion synthesis (Table S1, entry 21, Supporting Information, ) [31] were developed. The latter novel combustion synthetic approach delivered PSCs of remarkable PCEs of 18.82% and 19.84% for Cs 0.05 FA 0.81 MA0.…”