Spray deposition of NiOx hole transport layer and perovskite photoabsorber in fabrication of photovoltaic mini-module
Graphical abstract
Introduction
Perovskite solar cells are new entrants into the photovoltaic sector and have attracted the interest of both academic and industrial societies worldwide [[1], [2], [3]]. Organic-inorganic lead halide perovskite materials offer outstanding light absorption as well as charge carrier mobilities and lifetimes, thereby promoting high device efficiencies and opportunities for realizing a low-cost, industry-scalable technology [[4], [5], [6], [7]]. While the fabrication of Si-based photovoltaics entails high-vacuum and high-temperature deposition, solution-based processes can be employed to assemble perovskite solar cells; this enables the use of numerous well-developed coating and printing techniques such as spin coating, inkjet printing, blade coating, slot die coating, and spray-coating [8,9], thereby improving the potential for high production of perovskite solar cells with competitive performance. Although perovskite solar cells fabricated on the laboratory scale via spin coating exhibit staggering efficiencies on small aperture areas (<0.1 cm2), the full potential of this burgeoning technology cannot be realized without addressing the challenges inherent in its improvement, including that of assembling large-area cells or modules [[10], [11], [12]]. Moreover, processes commonly utilized in the laboratory are not available for high-throughput and large-scale manufacturing. Importantly, most devices with record efficiency were fabricated via anti-solvent dripping, which is not scalable [13]. Therefore, practical methods for realizing intrinsically low costs and versatile lab-to-manufacturing translation for upscaling the production of perovskite solar cells need to be explored.
To overcome the difficulties encountered in upscaling the deposition techniques employed for small-area cells, the process of spray-coating is considered appropriate [[14], [15], [16], [17], [18]]. It facilitates continuous and high-volume production and exhibits high compatibility with various substrates. Diverse processing parameters such as precursor formulation, flow rate, nozzle working speed and position as well as spray pathway can be controlled automatically, thereby ensuring superior control over the material deposition of assembled films and high throughput in the fabrication of perovskite solar cells [[19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30]]. To date, only a few studies have focused on improving the spray deposition method for fabricating perovskite photovoltaic modules comprising serially interconnected cells. Nevertheless, these works have demonstrated the promising outcomes of employing spray deposition for either the perovskite absorber layer [31,32] or the bottom contact layer (electron transport layer; ETL) [[33], [34], [35]] in devices with direct n-i-p architecture. Yang et al. conducted spray pyrolysis of TiO2 ETL and optimized the interconnection of four cells in series for the successful fabrication of a module with an aperture area of approximately 10.36 cm2 [35]. Tait et al. successfully fabricated monolithically interconnected perovskite modules (four sub-cells in series) with an active area of 3.8 cm2 via concurrently pumped ultrasonic spraying of a perovskite precursor solution [31]. It is important to assemble both the perovskite absorber layer and its adjacent contact layer via spray deposition to upscale perovskite-based solar cells to solar modules.
Nickel oxide (NiOx) is an efficient inorganic p-type semiconductor, which potentially functions as a hole-selective layer implemented in an inverted p-i-n perovskite device structure with the perovskite film group atop the NiO surface [36,37]. Herein, we fabricated an inverted perovskite solar mini-module through ultrasonic spray deposition of a NiOx hole transport layer (HTL) and a perovskite photoactive layer onto a large substrate (5.0 × 5.5 cm2). Firstly, compact and homogeneous undoped NiOx films were deposited onto indium tin oxide (ITO) glass via spray-coating with subsequent pyrolysis, allowing us to investigate the properties of NiOx. The optical, chemical, and electronic properties of the sol-gel-derived NiOx films varied with annealing time (3–15 min) at a fixed temperature. Secondly, the spray-coated MAPbI3 perovskite layer was integrated with the NiOx films and their interfacial/photovoltaic properties were investigated to verify the implantation of spray-coated NiOx and the resultant formation of the HTL and photoabsorber layers on a mini-module scale. This integrated spray-coating of the perovskite and sandwiched contact layers demonstrated a fabrication method for further upscaling to modules.
Section snippets
Sample and device fabrication
Patterned ITO substrates (5.0 × 5.5 cm2) were cleaned via sonication in diluted detergent, rinsed thoroughly with deionized water, acetone and isopropanol, then dried under N2 gas, and treated with O2 plasma for 6 min before layer deposition. The perovskite solar cells were prepared in ambient conditions (relative humidity, approximately 40%; temperature, 25 °C) with an inverted structure of ITO/NiOx/perovskite/C60/bathocuproine (BCP)/Ag. An NiOx layer, approximately 30 nm thick, was
Results and discussion
Combining our recent efforts to pursue scalable and high-throughput production of perovskite solar cells with large active areas (>1 cm2), the efficient fabrication of upscaled perovskite solar modules with an inverted planar architecture of ITO/NiOx/MAPbI3/C60/BCP/Ag is demonstrated in this study, wherein both the NiOx and MAPbI3 layers were deposited via ultrasonic spray deposition. Green solvent for the rapid and continuous processing of NiOx films was prepared from a diluted Ni-containing
Conclusions
In summary, we demonstrated a scalable ultrasonic spray-coating deposition for fabricating the NiOx HTL and perovskite absorber layer of a perovskite solar module with an inverted structure. The post-annealing duration strongly determined the surface characteristics of the spray-coated NiOx films. The optical properties and chemical compositions of the annealed films were explored to investigate the performance of NiOx as an HTL in a perovskite solar module. Module 4 corresponded to an optimum
CRediT authorship contribution statement
Li-Hui Chou: conceived the idea, performed the experiments, data, Formal analysis, and experimental planning, wrote the paper. Yu-Tien Yu: performed the experiments, data, Formal analysis, experimental planning. Itaru Osaka: conceived the idea, wrote the paper. Xiao-Feng Wang: conceived the idea. Cheng-Liang Liu: conceived the idea, wrote the paper, supervised the work, All authors contributed to the finalization of the paper.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors acknowledge the financial support from the Young Scholar Fellowship Program (Columbus Program) by Ministry of Science and Technology of Taiwan (MOST) in Taiwan, under Grant MOST 109-2636-E-002-029.
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