Nondoped Hole Transport Layer For High Performance Inverted Perovskite Solar Cells

Inverted?P-I-N?perovskite solar cells?PSCs?have great application potential due to the advantages of simple process,low temperature?<100??preparation,and compatibility with flexible substracts.In PIN-type planar PSCs,the hole transport layer?HTL?is critical to device performance.Commonly used hole transport layer materials are polystyrene sulfonate?PEDOT:PSS?,triphenylamine polymer?PTAA?,Ni O,etc.From previous reports:PTAA is an amorphous polymer with relatively low carrier mobility;PSCs prepared based on PEDOT:PSS devices have very small open circuit voltages?Voc?,about 1 V.Therefore,the hole transport layer material usually needs to introduce dopants or polar solvent treatment to enhance the conductivity of the thin film and improve the device photoelectric conversion efficiency?PCE?.However,the introduction of dopants not only increases the manufacturing cost but may greatly reduce the stability of the device.In addition,polar solvents may destroy the properties of the HTL material itself.Therefore,this paper focuses on the preparation of non-doped HTL,by optimizing HTL to obtain high-quality perovskite films,thereby enhancing the device PCE,mainly carried out the following two aspects of work:?1?In this work,undoped PTAA?1.5 W,2.5 W,10 W?with different molecular weights?Mw?was introduced as HTL,and the inverted planar PSCs were prepared with a simple one-step method.In the experiment,by adjusting the PTAA concentration of different Mw,the effect of the hydrophobicity of the PTAA surface on the quality and grain size distribution of the perovskite crystal,the trap state or the shallow trap energy level was studied.The result shows that lower Mw?1.5 W,2.5 W?PTAA is beneficial to obtain high-quality perovskite films.PSCs prepared with 2.5W-PTAA achieves a high PCE of18.11%and a Voc of 1.10 V.The hysteresis coefficient?HI?is as small as 0.32%.?2?In this work,PEDOT:PSS was mixed with deionized water to prepare high-performance HTL,thereby PSCs with excellent performance were successfully prepared.In the experiment,by adjusting the mixing ratio of PEDOT:PSS solution and deionized water,the film formation quality of PEDOT:PSS solution was optimized,and the perovskite film was deposited on the HTL with best performance.The effects of different proportions on the perovskite film and the performance of the entire device were studied.The result shows that the optimization of the perovskite film morphology is beneficial to reduce the loss at the interface between the HTL and the perovskite layer,thereby,effectively improving device performance.Compared with the undiluted PEDOT:PSS solution,the performance of the device prepared by PEDOT:PSS diluted with deionized water is significantly improved,and when PEDOT:PSS:H₂O=1:6 volume mixing,the performance is up to 17.28%.The average V_oc increased from 0.96 V to 1.03V,and the PCE increased from 12.61%to 15.97%.