Transient photoconductivity measurement in organic-inorganic hybrid perovskites for photovoltaic applications

R. D. ARCE; J. CARAM; N. BUDINI

Darmstadt

Congreso; Materials Science & Engineering Congress 2018 (MSE 2018); 2018

Lead?halide hybrid organic?inorganic perovskites (HOIPs) have recently emerged as highly efficient optoelectronic materials and are being intensively investigated as promising materials in optoelectronics, like photodetection, light-emitting diodes, laser devices and, mainly, for photovoltaic applications. In this latter field, most of the experiments performed on HOIPs films to study the electronic transport have been carried out on the photovoltaic cell as a whole device (Brenner,T.M. et al.). Despite the large amount of information available, there are still a number of subjects under debate in relation with transport properties of HOIPs. Of particular interest is to understand why these materials are so efficient in generating and transporting photocarriers. The study of transport in these materials as isolated films (i.e. not integrated to a device) may be an efficient way to deepen in the knowledge of perovskite?s properties.In this work we study the photoconductive response measured in coplanar configuration. Photoconductivity transients have been largely used to study carrier trapping in semiconductors films. There are, to our knowledge, no reports on the use of this technique to determine trap distribution in HOIPs.Samples of CH3NH3PbI3 were prepared using an equimolar solution of methylammonium iodine and PbI2. Films were deposited through the spin-coating technique in an inert atmosphere. The solution was dropped on a rotating glass substrate, which was previously covered with an interdigitated aluminum contact (distance between contacts was 50 microns). During the spinning process a drop of toluene was poured onto the film in order to get larger grains and good substrate coverage. Afterwards the samples were annealed for 3 minutes in a nitrogen atmosphere, and then mounted on a vacuum chamber for conductivity measurements. Photoconductivity measurements were performed under an illumination intensity of 100 W/cm2, provided by a tungsten halogen lamp.The transient photoconductivity was registered as the light was turned on and off. Transient characteristic times at room temperature were in the order of 20 to 30 seconds. Results were analyzed in terms of the generation-recombination models. A particular characteristic consisting in an overshooting in the onset of the photoconductivity has been observed, probably due to some photochemical reaction in the structure.