The Study Of Atomic Layer Deposition Technology In The Surface And Interface Of Photoelectric Conversion Device

In recent decades,devices which can directly converting solar energy into electricity have been recognized as an alternative energy source for our planet in the future considering the global shortage of fossil fuels.But the low-cost and high power conversion efficiency（PCE）appeared to be divided into two opposed systems rather into nations in traditional solar devices,like silicon devices.Professor Green gave a new concept which named third generation solar cell inclouding dye-sensitized solar cell,quantum dots solar cell,perovskite solar cell and photodetectors.Because of the great influence on the performance and stability of the devices,the interface engineering has been the focus of many scholars.We have a quite good study on the traditional silicon base solar cell,but because of the new optoelectronic devices involved in organic-inorganic composite system,which contains a variety of migration of the photogenerated carriers,composite and cell test of the interface between the hysteresis phenomenons,and can not fully use the existing system to explain and understand it.This lack of research on organic-inorganic composite interface,limiting our more deeply understanding and exploration of optoelectronic devices,it is necessary for us do some study to reveal the underlying physical mechanism.And the main results are listed below:1)We present a solution reaction process for high-yield synthesis of superlong Zn O nanobelts in a water bath at 90 ^oC followed by annealing at 500 ^oC.Then,the composites of the ZnO nanobelts and P25 TiO₂ nanoparticles are used as the photoanodes of DSSCs.Our results showed a large enhancement of 61.4%in conversion efficiency over the conventional TiO₂-based DSSCs.Furthermore,such composites were coated with a TiO₂thin film by ALD technique to improve interface connection in the system,and a significantly enhanced efficiency of 137%is achieved.We also systematically investigated the effect of the relative nanobelts/nanoparticles ratios on the performance of DSSCs,and a proposed mechanism is discussed in detail via current-voltage curves,incident photon-to-current conversion efficiency,reflectance and transmittance spectra,and electrochemical impendence spectroscopy（EIS）measurements.2)We employ ALD technique to deposit pinhole free,high transmittance,compact and ultrathin TiO₂ films as ETLs on FTO substrates.The CH₃NH₃Pb I_3-xCl_x and pristine P3HT are used as the light absorbing layer and HTL,respectively.The cells(glass/FTO/ALD-TiO₂/CH₃NH₃PbI_3-xCl_x/P3HT/Ag)show a high PCE of 13.6%.It is worthy to note that this is the highest efficiency reported for pristine P3HT（without doping）-based planar cells.The underlying mechanism for excellent performance is revealed by studying the effect of ALD TiO₂ thicknesses on the cell parameters including morphology of perovskite,transmittance,leakage current and electrochemical impedance spectroscopy（EIS）.Finally,a flexible device on the PET substrate with PCE of 7.2%is also demonstrated using amorphous TiO₂ films deposited by ALD at a very low temperature of 80 ^oC.3)We employ ALD technique to coat different thicknesses of TiO₂ films on BCPs.After an annealing process,BCPs are removed and mesoporous TiO₂ nanoworks are firmly attached on FTO substrates.For the first time,this novel TiO₂ network is used as the mesoporous frame for loading perovskite film.The thickness of frame can be adjusted precisely for effective infiltration of perovskite precursor.Usually a compact hole blocking layer is necessary before depositing a mesoporous frame,however,fabrication of present solar cells needs not this extra step.The CH₃NH₃Pb I_3-xCl_x and pristine Poly-3-hexylthiophene（P3HT）serve as the light absorbing layer and HTM,respectively.P3HT is cheap in price and easy to use and has been considered as a suitable HTM for perovskite solar cells than spiro-MeOTAD,which needs oxidation or doping treatment in ambient atmosphere.The cell(glass/FTO/ALD-TiO₂ nanostructures/CH₃NH₃PbI_3-xCl_x/P3HT/Ag)shows a high PCE of 12.5%compared with 9.83%of planar TiO₂ cells.It is worthy to note that the recombination rate decreases an order of magnitude than that of the planar cell.The underlying mechanism for excellent performance is studied by investigating the cell parameters including the thickness of ALD TiO₂ layer,morphology of perovskite,transmittance,leakage current and electrochemical impedance spectroscopy（EIS）.4)We report a high-performance CH₃NH₃Pb I₃ film based photodetector,which exhibits broad response for wavelength ranging from UV to visible light,high responsivity and large on-off ratio.By depositing an ultrathin Al₂O₃ film on the perovskite surface as protection layer using atomic layer deposition（ALD）technique,we successfully enhance its long-term durability up to two weeks in air.Furthermore,we firstly report an integrated self-powered all-perovskite system for simultaneous energy conversion and light detection.The present integrated system can work effectively at a low voltage less than 1.0 V and does not require external power source,possessing good photoresponse and high reproducibility.We provide a promising route to construct high-performance portable devices aimed at reduced size and weight.