Custom Synthesis of ZnO Nanowires for Efficient Ambient Air-Processed Solar Cells

Abstract

Nanostructuration of solar cells is an interesting approach to improve the photovoltaic conversion efficiency (PCE). This work aims at developing architectured 3D hybrid photovoltaic solar cells using ZnO nanowires (ZnONWs) as the electron transport layer (ETL) and nanocollectors of electrons within the active layer (AL). ZnONWs have been synthesized using a hydrothermal process with a meticulous control of the morphology. The AL of solar cells is elaborated using ZnONWs interpenetrated with a bulk heterojunction composed of donor (π-conjugate low band gap polymer: PBDD4T-2F)/acceptor (fullerene derivate: PC71BM) materials. An ideal interpenetrating ZnONW-D/A system with predefined specific morphological characteristics (length, diameter, and inter-ZnONW distances) was designed and successfully realized. The 3D architectures based on dense ZnONW arrays covered with conformal coatings of AL result in an increased amount of the ETL/AL interface, enhanced light absorption, and improved charge collection efficiency. For AL/ZnONW assembly, spin-coating at 100 °C was found to be the best. Other parameters were also optimized such as the D/A ratio and the pre/post-treatments achieving the optimal device with a D/A ratio of 1.25/1 and methanol treated on ZnONWs before and after the deposition of AL. A PCE of 7.7% (1.4 times better than that of the 2D cells) is achieved. The improvement of the performances with the 3D architecture results from both of: (i) the enhancement of the ZnO/AL surface interface (1 μm2/μm2 for the 2D structure to 6.6 μm2/μm2 for the 3D architecture), (ii) the presence of ZnONWs inside the AL, which behave as numerous nanocollectors (∼60 ZnONW/μm2) of electrons in the depth of the AL. This result validates the efficiency of the concept of nanotexturing of substrates, the method of solar cell assembly based on the nano-textured surface, the chosen morphological characteristics of the nanotexture, and the selected photoactive organic materials.

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

“…After careful adjustment of the main parameters of the ZnO NWs' growth, the final set 7 summarizes the corresponding PV cell characteristics. It is worth mentioning here that while varying NW growing time, precursor concentrations (zinc nitrate hexahydrate, HMTA, and PEI), the obtained ZnO NWs' properties, especially NW length and diameter values, were associated and are consistent with the range of previously published reports (see Figure S8) [23,[41][42][43][44][45][46]63,64,74]. The ZnO NWs' growing time should be limited to 6 h (0.4 µm long ZnO NWs) because longer NWs seem detrimental to the PV cell performance (Table 2).…”

“…The ETL also brings a specific processing step that has to be taken into account for large-scale developments. In the case of ZnO NWs, the hydrothermal growth required a starting ZnO seed layer, which can be formed by various techniques on different substrates, including conventional FTO-coated glass [41,[54][55][56]. However, zinc-oxide-based transparent electrodes such as AZO have been suggested to potentially act as efficient seed layers [48,57,58].…”

“…The perovskite infiltration, which should also ensure an optimal light-harvesting ability, is also a crucial parameter. Several groups have demonstrated perovskite solar cells based on such ZnO NW electrodes, which shows that the main growth parameters, such as hydrothermal precursor ratios and growing time, and growth solution concentration, significantly influence NWs' properties (i.e., NW length, diameter, density, and morphology) [41][42][43][44][45][46] and the device PV performances [17,23,47].…”

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

“…The initiation and stimulation of the ZnO NWs growth require a minimum of 1.15 h (i.e., 75 min). A shorter time do not lead to a well-organized, dense and uniform NW array [ 68 ]. Fig.…”

Template-based electrodeposited nonmagnetic and magnetic metal nanowire arrays as building blocks of future nanoscale applications

“…For the past few decades, nanomaterials ranging from nanoparticles to nanowires (NWs), have been a source of excitement in the scientific and research community, and captured imaginations in many current and emerging fields [11][12][13][14]. These nanomaterials are expected to be employed as ultraprecise, highly-efficient and nonvolatile components of next-generation state-of-the-art nanodevices, including racetrack memories [15,16], batteries [17,18], solar cells [19,20], capacitors [21,22], conductive electrodes [23,24], sensors [25,26], absorbers [27,28], magnetoresistive recording heads [29,30], and magnetologic gates and processors [31,32].…”