Study of Stable Tin-substitution Low-Bandgap Perovskite Planar-Heterojunction Solar Cells

Abstract

In this thesis in order to reduce the usage of heavy metal lead in perovskite active layer and extend the absorption wave range to sunlight we applied its group 14 congeners tin as replacement to produce high performance perovskite solar cells We partially substituted lead with tin content of 12 5% 25% 37 5% and 50% in the condition of retaining the perovskite ABX3 framework The band gap of perovskite material showed the red shift property with increasing of tin content; therefore it facilitates the absorption of solar spectrum Since element tin was involved in the precursor solution it would generate the ion Sn2+ and Sn4+ which is highly oxidized resulting in poor film formation and low coverage of perovskite active layer eventually inducing the drop of device power conversion efficiency However the higher film formation temperature of tin content perovskite was confirmed based on our experiment it created stronger bonding energy in perovskite structure enhancing the resistance against oxide and moisture and finally promoted device stability In this research we adopted XRD and secondary ion mass spectroscopy measurement to identify the element lead and tin substitution and we investigated the influence of different tin content on perovskite active layer by using absorption spectra surface roughness carrier transport characteristics and external quantum efficiency What’s more we adjust the precursor solution concentration and thermal annealing parameters besides applying nitrogen-spray two step annealing process to optimize the tin based perovskite device power conversion efficiency In the end of this thesis we successfully reduce the lead content in perovskite active layer while keeping quite good device efficiency 12 5% tin substitution perovskite exhibits comparable performance to pure lead perovskite with up to 10% PCE and 37 5% tin content perovskite performs over 85% of pure lead perovskite PCE Tin based perovskite provides a practical way for tandem solar cells or environment friendly perovskite solar cells in the future

Date of Award	2017 Aug 2
Original language	English
Supervisor	Wei-Chou Hsu (Supervisor)