The Study Of Interfaces And Their Effects On The Performance Of Perovskite Solar Cells

Perovskite solar cell?PSC?is one of the top ten science and technology breakthroughs of 2013 by Science.It's a new photovoltaic system which is expected to further reduce the price of photovoltaic power generation and PSC has great potential for commercialization.The emerging organic–inorganic hybrid PSC represents one of the transformative technologies of today.Like organic solar cells?OSCs?and dye-sensitized cells?DSSCs?,PSC is a lightweight,flexible and low-cost power source which can be fabricated through high-throughput solution process.So PSCs have attracted intensive research efforts from both academia and industry.The photoelectric conversion efficiency?PCE?of PSCs has rapidly improved from 3.8%to 22.7%in just 9 years,now rivalling the efficiency of silicon solar cells.The high PCE of PSCs mainly benefits from the excellent optoelectrical properties of perovskite,such as the strong optical absorption coefficient,a direct band gap,long carrier lifetime diffusion length,high electron/hole mobility and small exciton binding energy.By combining precisely controlling on the elemental composition,crystalline film formation,interface and device architecture,the highest PCE of PSC has reached the level close to its theoretical efficiency.To realize the commercialization of PSC,the stability of the device is the problem that needs to be solved urgently.At the same time,we also need to further enhance the performance and expand the application range of PSC to add some commercialization potentiality.This work begins with the introduction of PSC and then discuss the way to fabricate high efficiency PSC.The interface and its effect on the stability of PSC are followed.Further study is focused on the oxidation of PCBM to increase the open circuit voltage of PSC.The semitransparent PSC is also been studied in this work.Hope our work can push the commercialization of PSC a little bit.1.Firstly,the background and significance of the solar cells are briefly introduced.Secondly,the classification of the solar cells,especially the materials,structures,interfacial modification and operating principle of perovskite solar cells are reviewed in details.The challenges in PSCs and then the motivation and the innovations of this thesis are given.2.The light beam induced current?LBIC?method was adopted to nondestructively map the photoresponse of real planar organic-inorganic hybrid PSCs.It is found that the photoresponse of the devices is not uniform even though the morphology of the perovskite films from scanning electron microscope?SEM?or atomic force microscope?AFM?shows uniform character.This nonuniformity of photoresponse of the devices would be further exacerbated after degradation,which can be well traced by LBIC method.The indistinguishable morphology change during the device degradation indicates that the degradation of device is not mainly determined by the morphology of perovskite layer but the interface between perovskite and electrode.By using LBIC method,the worse performance area of the device is identified and then removed accordingly.The current density of the device can be enhanced from 19.44 mA/cm² to 21.72 mA/cm² after this clearance of the worse performance area.3.We proposed a simple method of oxidization of PCBM layer,which is commonly used in perovskite solar cells as the electron transport layer,to enhance the open circuit voltage(V_oc)of PEDOT:PSS-PCBM based inverted planar mixed halide perovskite solar cells.By simply oxidizing PCBM,the V_oc was enhanced from 0.93 to 1.05 V.The power conversion efficiency?PCE?thus was increased from 14.22%to 16.45%.This improvement was attributed to the lower charge carrier recombination rate and faster charge transfer at the interface after oxidation PCBM layer,as revealed by time resolved photoluminescence,transient photovoltage and transient photocurrent measurements.Ultra-violet photoelectron spectroscopy measurements indicated that about 0.12 V shift of the work function of PCBM after oxidation,supporting our conclusion.4.Semitransparent perovskite film was fabricated by thermal evaporation lead iodide film first.XRD and SEM showed that the perovskite film fabrication by this method had better crystallinity,larger grains size and uniform morphology than the traditional two-step perovskite film fabrication.The PCE of our initial device achieves7.14%,which needs to be further optimized.This work mainly discusses the progresses we have made in promoting the commercialization of perovskite solar cells.We emphasized the significance of our work of interfaces on the performance of PSC and then the commercialization of perovskite solar cells.