Preparation Of Copper Oxide Film And Study On Stability Of Perovskite Thin Film Solar Cells

Copper oxide(CuO)is a direct bandgap semiconductor material with an optical band gap of 1.4eV.In theory,the power conversion efficiency(PCEs)of solar cell based on CuO homojunction can reach up to 31%,In fact,the preparation process of n-type CuO is immature and the electrical properties of intrinsic(p-type)CuO is poor,which restrict the development of CuO solar cells;Organic and inorganic hybrid perovskite solar cells(PSCs)have attracted attention due to the excellent photoelectric properties of perovskite materials(CH3NH3PbI3).Now the PCEs of PSCs is above 22%,but the PSCs are facing air(H2O and O2)instability,thermal instability,which could dramatically restrict the future commercial application of PSCs.In this paper,n-type CuO thin films were prepared by pulsed laser deposition(PLD),the influence of Li doping on the electrical properties of intrinsic CuO was studied,the stability of PSCs was also studied.The results are as follows:First,CuO thin films were deposited on glass substrates by PLD and the influence of oxygen(O2)pressure on the structural,optical and electrical properties of the CuO films were studied.It was found that the film deposited at O2 pressure of 3×10 3Pa has pure Cu2O phase,whereas those deposited at 3-5Pa show mixed Cu2O-CuO phase,CuO phase can be obtained at 8-12Pa.The Hall effect shows that the film below 8 Pa exhibits p-type conductivity,8Pa or more exhibits a n-type conductivity.Gas sensing measurement results consistent with the Hall effect results.It shows that under a appropriate deposition conditions we can obtain n-type CuO.Second,in order to improve the electrical properties of CuO thin films,Li-doped CuO with different doping concentration was studied.The results show that Li doping does not affect the crystal structure of CuO,but it makes the grain size become larger.As Li doping concentration increases from 0 to 3wt.%,the band gap of the films decrease and then increase slightly.As the Li doping concentration increases from 0 to 2 wt.%,the carrier concentration increases from 3.11×1016cm-3 to 1.10×1019cm-3,the resistivity decreases from 319?·cm to 76?·cm.Continue to increase the doping concentration to 3wt.%,the concentration of carrier reduce to 8.62×1018cm-3,and the resistivity increase to 82.62?·cm.So,the optimum value of the Li doping concentration in CuO thin films is 2wt.%.Third,we studied the air stability and thermal stability of PSCs,a chemically vapor deposited graphene was inserted between Au electrode and spiro-OMeTAD in planar perovskite solar cells to block the diffusion of air and Au into perovskite layer,where the single layer graphene was transferred into the devices by a simple laminated process.After ageing in 45%humidity air for 96h or thermal annealing at 80? for 12h,more than 95%PCE of the devices with graphene can be maintained,which is much better than that of devices without graphene(?56%).The improved stability of devices with the graphene layer is attributed to the reduction of carrier recombination from decomposition of perovskite layer in air or Au doping perovskite layer under annealing treatment.Therefore,graphene is a promising ultra-thin barrier against air and metal diffusion,and has the potential application in photovoltaic devices,integrated circuit chips and light emitting diodes.