Low-Temperature Hydrothermal Growth of ZnO Nanowires on AZO Substrates for FACsPb(IBr)3 Perovskite Solar Cells

Abstract

Electron and hole transport layers (ETL and HTL) play an essential role in shaping the photovoltaic performance of perovskite solar cells. While compact metal oxide ETL have been largely explored in planar n-i-p device architectures, aligned nanowires or nanorods remain highly relevant for efficient charge extraction and directional transport. In this study, we have systematically grown ZnO nanowires (ZnO NWs) over aluminum-doped zinc oxide (AZO) substrates using a low-temperature method, hydrothermal growth (HTG). The main growth parameters were varied, such as hydrothermal precursors concentrations (zinc nitrate hexahydrate, hexamethylenetetramine, polyethylenimine) and growing time, in order to finely control NW properties (length, diameter, density, and void fraction). The results show that ZnO NWs grown on AZO substrates offer highly dense, well-aligned nanowires of high crystallinity compared to conventional substrates such as FTO, while demonstrating efficient FACsPb(IBr)3 perovskite device performance, without the requirement of conventional compact hole blocking layers. The device performances are discussed based on NW properties, including void fraction and aspect ratio (NW length over diameter). Finally, AZO/ZnO NW-based devices were fabricated with a recent HTL material based on a carbazole moiety (Cz–Pyr) and compared to the spiro-OMeTAD reference. Our study shows that the Cz–Pyr-based device provides similar performance to that of spiro-OMeTAD while demonstrating a promising stability in ambient conditions and under continuous illumination, as revealed by a preliminary aging test.

The impact of CBz-PAI interlayer in various HTL-based flexible perovskite solar cells: A drift-diffusion numerical study

“…Even though with this wider bandgap, the designed FPSC delivered an excellent efficiency (i.e., 28 %), and this confirms the possibility of enhancing the FPSC efficiency further (i.e., over 30 %) in the near future using the same proposed device design with various potential perovskite absorbers, including suitable ETL and HTLs, especially with CBz-PAI interlayer. Noticeably, this proposed work comprehensively focused on the perovskite/HTL interface enhancement using CBz-PAI interlayer; however, according to the published reports, mainly using ZnO NWs ETL-based real FPSCs still not exceeding the PCE of 15 % [ 56 ] due to several reasons, such as higher recombinations formed at the ZnO NWs/perovskite interface or the contact between ZnO NWs-ETL into the HTL (i.e., due to larger NWs length or lower perovskite absorber thickness) [ 57 , 58 ], etc. Therefore, further insightful studies are needed, mainly on the ZnO NWs/perovskite interface using passivation/interlayer similar to this study to enhance the FPSC efficiency further.…”

Control of ZnO nanowires growth in flexible perovskite solar cells: A mini-review

“…For example, solar cells require smooth and well-aligned ZnO NWs with an appropriate NW length and void fraction, offering an efficient electron transfer between the absorber and the top electrode [ 33 ]. For the ZnO NW synthesis, various physical and chemical methods have been considered, such as hydrothermal growth (HTG) and/or chemical bath deposition (CBD) [ 33 , 34 , [41] , [42] , [43] ], vapor-liquid-solid process [ 44 ], flame transport approach [ 45 ], pulsed laser deposition [ 46 ], molecular beam epitaxy [ 47 ], electrospinning [ 48 ]. For further details on ZnO NW growth techniques, one should refer to published reviews [ 7 , 32 , 36 , 43 , 49 ].…”

“…In the literature, many synthesis techniques are used for ZnO NW growth, such as hydrothermal deposition, vapor-liquid-solid process, flame transport approach and pulsed laser ablation [ 32 ]. Our group published several papers where the hydrothermal deposition method lead to well-aligned ZnO NWs for PSCs [ 33 ] and flexible PENGs [ 2 , 34 , 35 ], using different seed layers. Therefore, this review will focus on the limitations of the hydrothermal growth parameters to achieve optimal ZnO NWs for FPSCs and the impact of the seed layer on the latter ZnO NWs.…”

Hydrothermal preparation of oxide (Ga2O3, ZnO, TiO2) and derivative nanoparticles

“…Apart from that, ZnO nanoparticles are used in textiles due to their UV blocking properties, in sterilizing surroundings due to their antibacterial and antifungal activities, in cosmetics, food packaging, and biomedical applications [4,15]. ZnO material is also considered a preferred alternative to TiO 2 in some applications, including those of electron transport layer in perovskite solar cell, because it possesses energy levels and physical properties similar to those of TiO 2 , but requires lower temperatures for processing from solutions to achieve structures of different morphologies [16]. TiO 2 requires high processing temperature to achieve highly crystalline layers.…”

“…TiO 2 requires high processing temperature to achieve highly crystalline layers. In spite of that, TiO 2 is an important material for applications in solar cells, ultra-thin capacitors, optical devices, gas and chemical sensors, biomedical and self-cleaning coatings, and photocatalysis [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Apart from that, TiO 2 is widely used as pigment in paints, printing inks, cosmetics, papers, plastics, rubber etc.…”