Development Of The μSR Spectrometer Prototype And Its Application In Perovskite Solar Cell Materials

μSR(muon spin relaxation,rotation,and resonance)has become an important technology to study the atomic-level chemical and physical properties of condensed matter since the 1980s.Those techniques have been usually used to study magnetic materials,superconductors,ions transport,semiconductors,chemistry,and biological materials.Due to the high spin polarization(close to 100%for surface muons)of muons produced by a proton accelerator,μSR is especially suitable for studying the magnetism of condensed matter.μSR spectrometers are mainly located in four muon facilities(ISIS/UK,PSI/Switzerland,J-PARC/Japan,and TRIUMF/Canada).The successful construction of Chinese spallation neutron source(CSNS)provides a good platform for muon science researches based on its proton accelerator in China.The first Chinese muon source-EMuS(Experimental Muon Source)and the first 128μSR spectrometer prototype will be built in the high-energy proton application area of CSNS.In this thesis,the construction of the first Chinese μSR spectrometer prototype,including the overall design,electronics,detector and related tests will be introduced.The main results are as follows:we have completed the overall design of the 128-channel μSR spectrometer prototype and comfirmed the parameters of the key parts.According to the overall design,we completed the construction of one detector module,and finished magnetic shielding tests,noise tests,and SNR(ratio of signal to noise)tests.To test and optimize the detector’s capability of shielding external magnetic field,we proposed a new magnetic shielding test method based on 22Na radioactive source’s energy spectrum.Meanwhile,we also completed the design of the readout electronics,the production of hardware,the development of data acquisition software,and counting loss tests of electronics.Since EMuS is still under development,the detection system was sent to ISIS Muon Group and tested on their muon beam line for twice.The beam tests were successful,demonstrating that the detection system can work well.The dead time of the prototype detector was measured with a dedicated setup and measured to be 7.5 ns.The construction and tests of this μSR detection system have an important guiding significance for completing the construction of the whole 128-channel μSR spectrometer prototype in the next step.Muons are very sensitive to the fluctuation of local magnetic field of materials,so they are often used to study the transport of charged particles.At present,muons have been widely used to study the migration of lithium ions in lithium batteries.Muon scientists are exploring the application of μSR in the research of new materials,such as new solar cell materials.We followed the research hotspot closely and studied perovskite solar cell materials.Because EMuS is still under construction,we must carry out the μSR experiments in other muon facilities.The application for p,SR experiments is difficult,it will take a long time from the application to the beginning of the experiment.Another method is to use positron annihilation spectroscopy to study perovskite solar cell materials.Since 2009,the photovoltaic efficiency of solar cells with organic-inorganic hybrid perovskite as the absorber has been making breakthroughs.In a short period of ten years,the photovoltaic conversion efficiency has increased from 3.8%to 24.2%.It has a great application potential.Although significant progress has been made in a short period of time,there are still some key problems to be solved with perovskite solar cell materials.The primary challenge is that perovskite materials will degrade under the influence of humidity,oxygen,ultraviolet radiation and high temperature in real environment,which directly affects the stability and repeatability of battery devices.Another challenge is toxicity.At present,perovskite solar cell materials are basically lead-based and containing toxicity,which also restricts its commercial development.One of the main studies in this thesis is to focus on the stability of perovskite solar cell materials.The effect of Br doping on phase stability,defect density,and perf-ormance of FAPb(I1-xBrx)3 was investigated.The XRD measurements exhibit the enhancement of perovskite phase stability at x=0.05.However,the phase stability decreases gradually with Br content(x)over 0.05.With high absorbance and low defect density,the highest efficiency of 17.12%is achieved for FAPb(I0.95Br0.05)3 film.The PCE(Power Conversion Efficiency)increases by 25.7%compared to that of FAPbI3 film.There are also fundamental physical problems inside perovskite materials that still need to be clearly explained,such as hysteresis of current and voltage(JV)curve,defect characteristics,carrier dynamics and structural stability of the material,etc.Another important study in this thesis is to explore the internal dynamics of perovskite solar cell materials(MAPbBr3 single crystal)using the μSR spectroscopy and the corresponding theoretical calculations.Our studies have shown that MAPbBr3 single crystal is a highly dynamic material.Its internal organic molecular motion and structure fluctuation will change obviously by following the variation of temperature,which will have a great impact on its electrical properties.