Preparation and Functionalization of Hollow Silica Nanosphere Antireflection Coatings Towards Photovoltaic Applications

Author:Zhang Jing

Supervisor:dai ning lu yue zuo


Degree Year:2018





Antireflection(AR)coatings on encapsulant glass or flexible films of photovoltaic(PV)modules play important roles in the increase of output power.Both terrestrial and extraterrestrial PV modules inevitably face harsh environments,which demands of the AR coatings that they are humidity resistant,self-cleaning,anti-frosting,anti-icing,anti-abrasive,anti-dust/soiling,and atomic oxygen(AO)resistant as well as antireflective.In this dissertation,the preparation and functionalization of hollow silica nanosphere(HSN)AR coatings were systematically investigated from the following four aspects:(1)the low-temperature preparation of HSN AR coatings and the preparation of HSN AR coatings on flexible polymer substrates,(2)the study of mulitifuction of the HSN AR coatings such as the AO resistance in the space and the humid resistant,self-cleaning,and anti-dust properties under ground environments.The results and conclusions are summarized as follows:1.A low-temperature means(no more than 100°C)to remove the PAA templates in the HSN AR coatings was demonstrated by using H2O2 as an oxidation agent.Employing this approach,the HSN AR coatings were successfully prepared on the flexible PET substrates.The average transmittance from 300-1200 nm of the PET coated with HSN AR coatings could be increased by 7.95%compared with that of the bare PET.2.Applying the aforementioned low-temperature means,the HSN/PI composite coatings were successfully prepared via transferring the HSNs from glass to PI films.Compared with the pristine PI,the formation of HSN/PI composite coatings brought about the improved optical,mechanical,and AO resistant properties:the composite ones showed an average transmittance of 92.43%at wavelengths of 400-1600 nm,a Young’s modulus of 7.1 GPa,and a hardness of 0.51 GPa,which were superior to those of the pristine PI,90.80%,3.7 GPa,and 0.26 GPa,respectively;in addition,the mass loss of the composite ones,35μg/cm2,was two orders of magnitude lower than that of the pristine,1129μg/cm2,after an AO exposure of 6.05×1020 atoms/cm2.3.The humidity and abrasion resistant AR coatings with good thermal stability were prepared via a well-controlled dual precursor modification/hybridization process of HSNs.The dual precursor-derived AR coatings(TMHSN)annealed at 400°C for 1h exhibited an average transmittance(Tave)of 97.21%at wavelengths of 400-1100 nm,an enhancement of 5.96%relative to the bare glass,and the water contact angle was maintained at 105°.No degradation in Tave and macroscopic scratch were observed from the TMHSN AR coatings after a scrub test of 1000 cycles.Only a small relative reduction of 0.6%in Tave were exhibited after an ultra-long highly-accelerated humidity and temperature stress test of 120 h,equivalent to a 5000 h damp heat test at a temperature and a relative humidity of 85°C and 85%,respectively.To the best of our knowledge,the comparable durability has not been reported yet in the literature.4.Effects of pore structure,surface roughness,and chemical states on anti-dust and self-cleaning properties of AR coatings were systematically studied via two groups of comparative experiments:(1)the HSN and solid silica AR coatings and(2)the hydrophilic and hydrophobic(via a surface chemical modification with either–F or-CH3 groups)HSN AR coatings.It was found that:(1)the HSN AR coatings with the closed-pore structure and rough surface exhibited a better anti-dust property compared with the solid silica AR coatings with the open-pore structure and smooth surface;(2)the hydrophilic AR coatings showed the self-cleaning properties,whereas the hydrophobic AR coatings did not in a Ningbo climate;(3)the–F grafted AR coatings showed an electrostatic potential of-0.11 to-0.15 kV,possibly bringing about the dust accumulation due to an electrostatic force;a larger relative reduction in Tave of 2.32%was observed compared with that of the bare glass,1.72%,after an indoor dust experiments;in contrast,no electrostatic potential was observed from the–CH3 grafted AR coatings while only a less relative reduction of 0.25%in Taveve was shown,compared with that of the hydrophilic HSN AR coatings,0.5%,after the dust experiments.The above results are of originality.The novel approach was proposed to enhance the optical transparency and the AO-resistance of flexible PI films that applied in lightweight solar arrays in space.On the other hand,the studies are instructive to understanding on the interaction between AR coatings on terrestrial PV modules and harsh environments,and pave the way towards the long-term use of AR coatings.