Study Of Light Absorbers And Interface Engineering Of Mesoscopic Perovskite Solar Cells

Organic-inorganic hybrid perovskite compounds have attracted tremendous attention,since their incorporation into photovoltaic?PV?devices by Miyasaka et al.in 2009.The power conversion efficiency?PCE?of perovskite solar cells?PSCs?has increased rapidly from 3.8%to 23.7%in a short time.Some key attributes of these perovskite compounds include ease of fabrication,strong solar absorption,low non-radiative carrier recombination rates and high carrier mobility.In addition,the good solubility owing to their ionic nature enables different low-temperature solution processes,such as spin coating,blade coating,slot-die coating,screen printing etc.PSCs can be divided into two types,planar and mesoporous PSCs.Actually,PSCs using mesoporous metal oxides have given an exhibition of very high PCE up to now.In the development of mesoporous PSCs,fabrication of perovskite absorber layers with a complete pore filling as well as a well-defined grain structure,full surface coverage,and compact capping layer is pivotal to realize efficient solar cells.In this dissertation,we develop various types of surface modification and interface engineering methods to modulate nucleation and crystal growth kinetics of perovskite thin films on mesoporous TiO₂,improving the quality of light absorbers,enhancing the solar absorption and carrier mobility,decreasing carrier recombination rates and defects at the surface and interface,and thus greatly improving the PV performance of PSCs.Detailed description of the research is listed as following:1.The characteristic properties of MgO passivation films on mesoporous TiO₂using different concentrations of metal-organic magnesium acetate and their effects on the PV performance of low temperature?LT?carbon based PSCs has been studied in order to reduce the cost,decrease energy consumption,overcome metal-migration induced degradation and the recombination of photo-generated electrons and holes.The MgO-TiO₂ hybrid film obtained with a 90 mM magnesium acetate worked as the most efficient charge extracting and transporting layer,and achieved the best performance in PSCs.Compared to the device without MgO modification,the PSCs assembled with the optimized MgO-TiO₂ hybrid blocking layer showed improvement in J_SC(from 18.80 mA cm^-2 to 20.01 mA cm^-2),FF?from 0.57 to 0.64?as well as in V_oc?from 0.83 V to 0.95 V?,resulting a much better conversion efficiency of 12.17%.2.In order to maximize the light absorption,charge separation and collection and voltage output,highly efficient plasmonic perovskite solar cells?PSCs?were designed and fabricated.The solar cells were prepared by incorporating Au nanoparticles?NPs?into mesoporous TiO₂ films and then,depositing a MgO passivation film on the Au-NP-modified mesoporous titania via wet spinning and pyrolysis of magnesium salt.The PSCs obtained by combining Au-NPs and MgO demonstrated a high power conversion efficiency of 16.1%,with both a high open-circuit voltage of 1.09 V and a high short-circuit current density of 21.76 mA cm^-2.The device achieved a 34.2%improvement in the power conversion efficiency compared with a device based on pure TiO₂.Au-NRs and Ge-NP modified PSCS were fabricated for comparative studies.Efficient Ge-NPs based perovskite devices were obtained with an average power conversion efficiency?PCE?of 18.82%,demonstrating over 7.4%enhancement,compared with the reference device without modification.The related PV performance enhancement mechanisms behind the PSC device based on Au and Ge nanomaterials were discussed.3.Considering the issues of stability,perovskite surface defect states due to uncoordinated ions,and the interfacial recombination between TiO₂ or perovskite/HTM interface,1,4-benzenedicarboxylic acid?terephthalic acid,TPA?was used as an additive for the deposition of perovskite layers.The PCE and the stability of LT?100??carbon based PSCs are considerably improved by using TPA additive and applying insulating MgO as passivation film for mesoporous TiO₂.The addition of TPA additive simultaneously facilitate nucleation and modulate the kinetics of crystal growth from solutions,enabling preparation of smooth and compact perovskite morphology with improved crystallization,grain uniformity,loading of perovskite into the TiO₂ mesopores and coverage area.The performance of the PSCs is significantly improved with the mean efficiency increasing from 11.5%for the control structure to 14.29%for the TPA modified structure.4.In order to improve the ultraviolet?UV?and ambient air stability of perovskite solar cells,SnO₂-NR arrays were fabricated by an aqueous synthesis method in the presence of hydrochloric acid and using thin compact SnO₂ as seeds.The influence of HCl concentration on the photovoltaic?PV?performance of the SnO₂-NR array based PSC device was investigated.The formed crystalline SnO₂ nanorods with square transversal-sections were oriented on the FTO facets in a well-defined and perpendicular fashion at an optimal HCl concentration.Consequently,efficient and stable SnO₂ nanorod based perovskite devices were obtained with an average power conversion efficiency?PCE?of 16.57%.The SnO₂ nanorod array based PSCs demonstrated considerably better UV and ambient air stability than the planar SnO₂and notably mesoporous TiO₂ solar cells.