湿度环境下钙钛矿太阳能电池薄膜微结构演化的同步辐射原位实时研究

环境湿度对有机-无机杂化钙钛矿薄膜太阳能电池稳定性有着相当重要的影响,在湿度环境下原位实时观测钙钛矿薄膜微结构的演化有助于揭示湿度导致的器件性能衰减的微观机理.本文基于上海光源X射线衍射线站,建立了一套湿度可调可控的原位X射线衍射实验装置用以实时观测湿度环境下钙钛矿薄膜的微结构演化.在相对湿度为60%±2%的环境中,采用原位同步辐射掠入射X射线衍射发现在钙钛矿薄膜暴露在湿度环境的最初阶段,其(110)衍射峰附近逐渐出现了中间相结构,应该是来源于部分钙钛矿晶体结构的逐渐分解所形成的钙钛矿多相结构;同时,紫外可见吸收光谱实验表明,经环境湿度处理后的薄膜吸收有所降低,尤其是在约770 nm处吸收台阶发生蓝移,在一定程度上反映出钙钛矿晶体结构的减少或结晶性变弱;扫描电子显微镜结果进一步显示,湿度实验后薄膜形貌的均匀性明显变差,覆盖率降低、孔洞变大及晶界变明显;采用环境湿度实验前后的钙钛矿薄膜上制备的太阳能电池J-V性能测试结果显示,器件的填充因子和光电转换效率均由于环境湿度处理降低了30%以上.因此,同步辐射原位实验观测清晰地揭示了器件性能与钙钛矿薄膜形貌以及微结构演化的密切关联,为理解有机-无机杂化的钙钛矿薄膜的降解微观机理提供了实验依据和指导.

An in-situ real time study of the perovskite film micro-structural evolution in a humid environment by using synchrotron based characterization technique

Humid environment plays a vital role in affecting the performance stability of the organic metal halide perovskite solar cells. Therefore, in situ monitoring the micro-structural evolution of perovskite film in real time will help to reveal the micro-mechanism for the device performance decay induced by humidity. A device providing a controllable humid environment has been set up at X-ray diffraction beamline of Shanghai Synchrotron Radiation Facility, which is used to monitor in situ the perovskite film micro-structural evolution in real time in a humid environment by using grazing incidence X-ray diffraction(GIXRD). After a perovskite film is exposed to the environment with a relative humidity of 60%±2%, a new component emerges near the perovskite(110) diffraction peak in the early stage of the exposure, which is observed for the first time. This new component is attributed to the perovskite intermediate phase structure transformed from the gradual degradation of the perovskite crystalline. Meanwhile, UV-Vis absorption measurements show that humidity causes the absorption of the film to decrease slightly with the blue shift of the absorption edge at ~770 nm, which indicates a reduced amount of perovskite crystalline or a decrease of perovskite crystallinity. Scan electron microscope further demonstrates that the film after the humid exposure presents a worse morphology with a lower coverage, bigger pores, and larger voids between crystalline than the pristine film. The current-voltage(J-V) measurements of the solar cells fabricated on the perovskite films before and after the humid exposure show that both the filling factor and the power conversion efficiencydecrease by over 30% due to the humidity. The present work demonstrates that the close relationship between the device performance and the perovskite film microstructure as well as their morphologies can be studied very well by in-situ synchrotron based characterization technique. The present study could lay a good foundation for the understanding of the degradation mechanism for the organic metal halide perovskites.