Study On Bulk Heterojunction Solar Cells Based On TiO₂ Nanorod Arrays/PbS Quantum Dots

The theoretical efficiency of quantum dot solar cells is as high as 44%due to the multi-excition effect.In theory,the quantum dot solar cell can break through Shockley-Queisser limit?31%?,therefore,it is called the third generation photovoltaic device.Traditional planar heterojunction solar cells are limited by carrier transmission distance,the thickness of active layer is usually limited to 200-300 nm,which leads to lots of photons cannot be effectively utilized.On the other hand,the performance of photovoltaic devices is closely related to the extraction and transmission of carriers,the energy level structure and interface properties of each functional layer in photovoltaic devices directly affect the extraction and transmission efficiency of carriers.In order to solve these problems,a bulk heterojunction quantum dot solar cell with TiO₂ nanorod array as photoanode was designed in this paper.The effect of surface morphology of photoanodes on quantum dot solar cells was studied.The PbS quantum dots capped by ZnS was synthetized on photoanode using successive ion layer adsorption and reaction method?SILAR method?.The effect of synthesis parameters of SILAR method on device performance is analyzed.The main contents are as follows:?1?The effect of hydrothermal reaction time of TiO₂ nanorod arrays on the performance of solar cells was studied.The results show that the nano-TiO₂ films prepared by hydrothermal method are single crystal rutile nanorod arrays which grow preferentially along[001]crystal direction.When the hydrothermal reaction time is 3 h,the nanorods are arranged orderly,the density is moderate,and the film quality is the best.Moreover,after filling quantum dots by SILAR method,the optical absorption of quantum dots reached the maximum.At the same time,the key properties such as crystal structure and surface morphology of hydrothermal synthesized TiO₂ nanorod arrays were investigated.?2?Optimizing the experimental parameters for the synthesis of quantum dot films and hole conducting layers.PbS quantum dot film was deposited on the surface of TiO₂nanorod arrays by SILAR method.The effects of the SILAR rounds and the cycles of PbS and ZnS on the surface morphology,microstructures and optical properties of the films were investigated.The results show that under the deposition parameters of[PbS?5?/ZnS?5?]3,the core-shell structure of PbS quantum dots with uniform size distribution can be prepared.Finally,a solid-state in-situ synthesized quantum dot solar cell was fabricated using PEDOT:PSS as the hole conducting layer and carbon paste as the counter electrode.Under simulated AM1.5G solar irradiation,the photoelectric conversion efficiency?PCE?of photovoltaic devices reaches 1.4%.The results show that the distance of electron transmission can be greatly increased by using TiO₂ nanorod arrays as photoanode.The thickness of active layer can reach630 nm,and the utilization of incident photons can be improved.The size of core-shell structure PbS/ZnS quantum dots and the interface energy level structure can be controlled by SILAR method.Therefore,the extraction and transmission efficiency of carrier are improved,and the best device performance is obtained.