Interfacial Modification And Spray-based Preparation Technology Of Organic Lead Halide Light Harvester Layers For Perovskite Solar Cells

Organic-inorganic hybrid perovskite is a kind of solution processability, high carrier mobility semiconductor materials. Perovskite solar cells have simple device stucture, which exhibit wide spectral response range and high photon-to-electron conversion efficiency（PCE）. The PCE of perovskite solar cells recently have been improved above 20%, which approach the performance of c-Si solar cells and CIGS solar cells. Interfacial modification enhancing the carrier collection efficiency, improving the quality of perovskite light harvester layer with a modified fabrication technology or optimizing the composition of the perovskite light harvester layer can improve the performance of the devices. In this paper, we prepare high performance perovskite solar cells summaried in the follow methods.1, Organic-inorganic hybrid perovskite also can be an hole conductor besides light harvester. So, hole conductor free perovskite solar cell can be prepared. This kind of device has lower cost than the normal perovskite solar cell as a result of that the expensive hole conductor materials are not used. However, gold electrodes need to collect holes from the perovskite layer directly. This process is very difficult, which may lead to poor device performace. We show a Li TFSI solution treatment for improving the interfacial contact between CH₃NH₃ Pb I3–x Clx and Au. This method can effectively enhance the carrier transport at the CH₃NH₃ Pb I3–x Clx/Au interface and improve the device performance. SEM images show that uniform nanodots are formed at the surface of CH₃NH₃ Pb I3–x Clx films after the Li TFSI solution treatment. Mott-Schottky and electrochemical impedance analysis show this treatment can decrease the barrier height and charge transfer resistance at the CH₃NH₃ Pb I3–x Clx/Au interface. It expains how the Li TFSI solution treatment improve the carrier collection efficiency. Finally, the PCE and fill factor of hole conductor free perovskite solar cell is enhanced from 4.0% and 0.36 to 7.6% and 0.64 by the Li TFSI solution interfacial modification. Moreover, this Li TFSI solution treatment is also effective in perovskite photodetector, which can enhance the light response intensity.2, CH₃NH₃ Pb I3（MAPb I3） is a widely investigated perovskite material as light harvester layers for perovskite solar cells. The quality of MAPb I3 film is a key for the corresponding device performance. Moreover, the preparation process will affect the quality of MAPb I3 film. In this paper, we show a spray reaction-based solid/mist interface reaction, which can repeatedly fabricate high quality MAPb I3 films at a low reaction temperature, and the reaction conditions can be facilely controlled. Detail studies reveal that the volume of MAI solution and the reaction temperature control not only the extent of reaction but also the morphology and crystallization of the MAPb I3 film. Under optimized conditions, pinhole-free MAPb I3 films with high crystallization can be obtained. Based on this solid/mist interface reaction method, the perovskite solar cells reach a best PCE of 16.2% with an average PCE of 14.9%. Furthermore, planar junction perovskite solar cells are also fabricated using this method. The excellent efficiency of 14.9% confirms the availability of the solid/mist interface reaction method.3, We prepare a series of FA_1-x Csx Pb I3（x=0, 0.1, 0.2 and 0.3） solid solution by an interface reaction method based on the spray technique. XRD patterns show that the 2θ angle of diffraction peak increases with the increase of Cs+ ions concentration, which is due to the Cs+ ions incorporation relax the extension in the Pb I6 matrices and reduce the lattice constant. Moreover, XRD patterns and SEM images show that FA0.9Cs0.1Pb I3 film has the best crystallinity and it is composed of the largest average size perovskite grains. Absorption spectra of FA_1-x Csx Pb I3 films and IPCE of the corresponding devices show that 10% Cs+ ions incorporation can enhance the 600 nm ⁸00 nm wavelength light utilization efficiency. Electrochemical impedance spectra show FA0.9Cs0.1Pb I3-based device has the largest recombination resistance, which indicates its lowest recombination rate. Moreover, Cs+ ions incorporation can decrease the charge transfer resistance at the interfaces of selective contacts. Finally, FA0.9Cs0.1Pb I3 perovskite solar cells obtain an average PCE of 14.2%, which is much higher than that of FAPb I3 perovskite solar cells（11.3%）. Furthermore, these two kind of devices are aged in 50% humidity and 20 oC environment for 100 hours to study their stability. After the 100 hours aging process, most α-phase FAPb I3 change into δ-phase FAPb I3, and FA0.9Cs0.1Pb I3 still keep its pure α-phase structure. It indicates FA0.9Cs0.1Pb I3 and the corresponding device show much better humid stability than FAPb I3.