Temperature effect of the compact TiO2 layer in planar perovskite solar cells: An interfacial electrical, optical and carrier mobility study

The power conversion efficiency of TiO2 based organo-lead halide perovskite solar cells has already surpassed 20% by utilizing low temperature solution processing techniques. However, the electronic structures and exciton/electron transport mechanism at the TiO2/perovskite interface are not fully understood. In this report, simple planar TiO2/perovskite heterojunctions are fabricated with different TiO2 compact layers followed by studies of their effect on the charge extraction/transport properties of the deposited heterojunctions. Efficient perovskite solar cells based on these TiO2/perovskite heterojunctions [with CH3NH3PbI3 and FA0.81MA0.15Pb(I0.836Br0.15)3 films] have been fabricated and the devices exhibit reproducible efficiency values and good stability. The impact of interfacial potential barrier and TiO2 surface properties on photogenerated carrier transport mechanisms and overall power conversion efficiency of perovskite solar cells is investigated by using comprehensive electrical and optical characterization methods such as SEM, XRD, XPS, Raman spectroscopy, TRPL, TAS and TPD. Obtained results indicate that efficient device can be fabricated by optimizing of TiO2 annealing conditions.

Perovskite materials [CH3NH3PbI3 and FA0.81MA0.15Pb(I0.836Br0.15)3] are utilized to fabricate efficient planar perovskite solar cells based on different TiO2 layers. The crystal composition and structure difference in TiO2 samples with different annealing temperatures are studied by using excellent morphologic, atomic, electronic experimental methods. The evidence of strong interface dipole effect (potential interface barrier) at the various CH3NH3PbI3/TiO2 interfaces is observed with the help of some optical experiments. Based on the obtained results, the comprehensive exciton/free electron transport mechanisms at these TiO2/CH3NH3PbI3 interfaces are presented for the first time.226