All-mesoporous Perovskite Solar Cell And Its Improvement For Efficiency

Solar cells are the devices that can convert energy of sun radiation to the electricity.In photovoltaics?PV?,the term“efficiency”is used to describe the amount of electricity that solar cell can convert from the incident light.There is a great demand from the market to create cheap,while at same time efficient,solar cells.As for now,the highest level of efficiency the solar cell can achieve,is up to 25%.There exists a vast classification of solar cells,based on different devices architecture,materials that had been used and their working principle.The main purpose of this thesis is to introduce one of the most prominent and innovative type of solar cells–the perovskite solar cell?PSC?.PSCsmake use of a kind of material,called perovskite,to act as light absorbing layer for generating the electron-hole pair,which later will be separated and redirected to positive and negative contacts of the cell respectively.The aim of this work is to concentrate on one of the most perspective type of PSC–all mesoporous structured PSC,in which most of the functional layers have porous structure and infiltrated with perovskite.Such type of structure has its advantages over conventional PSC.To understand how all-mesoporous type of PSC can be improved,series of experiments were performed.During experimental part of this work,the basic mesoporous structure was used,consisting of dense and mesoporous TiO₂ layers acting as electron transport layers?ETL?,mesoporous NiO acting as holes transfer material?HTM?and porous composite carbon materials layer acting as counter electrode?CE?.These layers were subject of optimization in order to achieve higher level of solar cell efficiency.Particularly,dense TiO₂,also called as“blocking layer”,was studied by comparing its deposition techniques-conventional spin-coating and by oxidation of magnetron-sputtered Ti.Mesoporous and blocking TiO₂ layer was subject of optimization by applying TiCl₄ treatment to this layer,with comparison of how the duration of treatment had influenced devices'PV characteristics.The optimal time of treatment was identified and the possible reasons were tentatively discussed.Organoleadhalid perovskite solar cells with all-mesoporous device structure were fabricated with TiO₂ blocking layer created by two different methods.Three groups of devices were tested.The TiO₂ blocking layer of group 1 was spin-coated with conventional method,while that of groups 2 and 3 was grown by magnetron sputtering of metallic Ti and followed thermal oxidation.Different durations?0,30,45,and 60 minutes?of TiCl₄ treatment were used during fabrication to study how the performance of each group of solar cells was affected.For all groups of samples,it was obvious that treated samples had much better I-V characteristics that non-treated,with up to 50%improvement in the power conversion efficiency?PCE?.The difference in the performance improvement was also investigated.NiO layer thickness was further optimized,and the relation between this layers thickness and PV characteristics was discussed as well.CE as a layer,consisting of different carbon materials,such as graphite,carbon black?CB?,multi-walled nanotubes?MWCNT?,was also optimized by analyzing how the overall PSC devices'performance was influenced by these materials weight ratios.Therefore,by optimizingall the functional layers,the performance improvement of an all-mesoporous PSC device was investigated.