The Research On Design Of Ferroelectrics Based Photovoltaic Devices And Polarization Tunable Charge Transport

Organic-inorganic halide perovskites have emerged as a champion light absorbing material due to the suitable band gap and the large absorption coefficient in the visible light region.However,large-scale applications of the perovskite photovoltaic techniques still face chemical and mechanical instability challenges including the instability against moisture/air and temperature.Combining the experimental and theoretical methods,the photovoltaic and point defect properties of BaMX₄ are studied,as well as polarization tunable interfacial transfer and photovoltaic performance.The main research contents are shown as follow:The band gaps,light absorption coefficients and SLME of BaMX₄（M=Co,Ni,Fe,Mn;X=F,Cl,Br,I）are calculated using density functional theory.Three Barium fluorides,i.e.,BaNiBr₄,BaMnCl₄ and BaCoF₄ are considered to possess desirable photovoltaic properties.Furthermore,we fabricate the thermodynamically stable BaCoF₄ and verify the theoretical prediction results.Besides,defect properties of BaCoF₄ are also studied using DFT calculations.We found that BaCoF₄ exhibits clear n-type self-doping property,which can result in an enhanced electron transfer.Indeed,our experiments confirm the good photovoltaic performance of BaCoF4-based solar cells due to the n-type self-doping of BaCoF₄.In addition,the traditional inorganic ferroelectrics BaTiO₃ is incorporated into organo-inorganic hybrid perovskite solar cells as an electron transport layer.We theoretically simulate the carrier transport in BaTiO₃/FAPbI₃ heterojunction upon different poling.The charge transfer based on triplet excited states suggests that polarization in different directions（P₊or P_-）tends to form different type II band alignment of BaTiO₃/FAPbI₃ heterostructure which enhances or screens the built-in field and further adjusts the charge transfer across the interface.The suitable conduction band offset（CBO）of FAPbI₃/BaTiO₃ heterostructure leads to high theoretical efficiency approaching to²3%.Finally,the BaTiO₃ based perovskite solar cell is fabricated.We exert alternating poling bias for the BaTiO₃ based devices with different poling strengths and investigate the photovoltaic performance of them.The devices upon positive poling exhibit enhanced photocurrent and open circuit voltage while the negative poling decreases the photovoltaic performance,proving the ferroelectric tunable photovoltaic performance of BaTiO₃ based devices.