| Integrating sustainable cellulose materials into electronic devices is a hot research topic in academic communities.Highly transparent cellulose film with high transmission haze is a kind of paper with special optical properties.In addition to the advantages(degradability,low cost,flexibility,light weight,etc.)of ordinary paper,it also presents high transparency and strong light scattering behavior(high transmission haze),and has the potential to use in solar cells as a green optical transparent material to improve the power conversion efficiency.However,due to the lack of systematic research on the influencing factors of haze of highly hazy and transparent cellulose films,the haze formation mechanism is not clear,which restricts the industrialization process of this kind of films.Therefore,the study of haze formation mechanism of cellulose-based transparent films can provide a scientific basis for the development of large-scale preparation methods of highly hazy and transparent cellulose films.In this work,the fiber structure is modulated by chemical and mechanical treatments(2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO)oxidation,screening,cooking,bleaching,ion exchange treatment),while the configuration of the transparent cellulose film is tailored by a combination of papermaking technology and paper-converting methods(vacuum filtration,impregnation),and the relationship between the structural parameters of wood fibers(the size of fiber crystal structure,fiber length and width,fine content,degree of polymerization(DP),etc)and transparent film(film thickness,surface roughness,porosity,internal crystal structure,etc)and transmission haze is studied.Then,the main factors affecting the haze of transparent cellulose film were analyzed according to the experimental data,and the haze formation mechanism of transparent cellulose film was expounded.Finally,the highly hazy and transparent cellulose film was applied to the solar cells through laminating method and the influence of haze on the performance of solar cell was explored.The main conclusions are as follows:(1)The relationship between the haze of transparent cellulose film and fiber structure was studied.The micron-sized crystal structure of the fiber was the dominant factor for the haze,and as the size of the fiber crystal structure increased from nanometer to micron,the film haze increased increased significantly from 11.4% to 82.8%.With the decrease of the fiber size(fiber length decreased from 2.348 mm to 0.697 mm,fiber width decreased from 30.2 ?m to 24.9 ?m),the haze of the transparent film decreased from 83.1% to 71.9% gradually.The degree of polymerization(DP)of cellulose almost has no effect on the haze of transparent cellulose film.(2)The effect of the structure of transparent cellulose film on its haze was studied.The porosity was an important influence factor of haze,and with the increase of the porosity(from24.7% to 39.3%)of the transparent film,the haze of the film increased dramatically from 68.6%to 95.7%.The crystal structure inside the film also significantly contributed to the haze of transparent cellulose film.With the decrease of the number,size and uneven distribution of the crystal structure inside the film,the haze of transparent film gradually decreased.As the film thickness increased from 36.2 ?m to 105.3 ?m,the haze of transparent cellulose film increased from 83.3% to 89.5% gradually,but the increase is limited,indicating that the film thickness was not the main influence factor of haze.When the transparent cellulose film based on micronsized fibers has a micron scale surface roughness,the surface roughness had almost no effect on its haze.(3)The haze formation mechanism of highly hazy and transparent cellulose film is clarified.According to the studies in(1)and(2),the internal crystal structure and porosity of the film are the main factors affecting the haze of transparent cellulose film.Combined with Mie scattering,the formation mechanism of haze can be clarified through comprehensive analysis: the high haze is ascribed to the uneven distribution of refractive index in the transparent cellulose film that caused by plenty of micron-sized cellulose crystal structure and a small number of micron/sub-micron pores.Under the guidance of the haze formation mechanism,from the perspective of retaining the original structure of wood fibers and increasing the proportion of micron-level crystalline structure and its uneven distribution,a transparent all-cellulose composite film with an ultra-high haze is presented by infiltrating regenerated cellulose(RC)with undissolved microscale fibril bundles into the porous structure of common paper.The composite film displayed a 90.1% transparency and a 95.2%transmission haze,which was close to the theoretical limit(?100%),and the haze formation mechanism was further verified.(4)Transparent cellulose film with high haze was applied to the light management of solar cells,and the effect of film haze on the performance of solar cells was investigated.When laminating a highly hazy and transparent cellulose film on the perovskite solar cells,the performance of the cells(including PCE,FF,Isc and Voc)was improved.The PCE of the solar cells increased from 19.26% to 20.84%,with an increase of 8.2%.Moreover,when the light transmittance of the film used for light management is similar,the enhancement of film haze is helpful to improve the PCE of solar cells. |
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