Shargaieva, Oleksandra; Lang, Felix; Rappich, Jörg; Dittrich, Thomas; Klaus, Manuela; Meixner, Matthias; Genzel, Christoph; Nickel, Norbert H.: The influence of the grain size on the properties of CH3NH3PbI3 thin films. ACS Applied Materials & Interfaces 9 (2017), p. 38428-38435
10.1021/acsami.7b10056
Abstract:
Hybrid perovskites have already shown a huge success as an absorber in solar cells, resulting in the skyrocketing rise of power conversion efficiency to more than η = 22%. Recently, it has been established that the crystal quality is one of the most important parameters to obtain devices with high efficiencies. However, the influence of the crystal quality on the material properties is not fully understood. Here, the influence of the morphology on electronic properties of CH3NH3PbI3 thin-films is investigated. Post-annealing was used to vary the average grain-size continuously from ≈150 to ≈1000 nm. Secondary grain growth is thermally activated with an activation energy of Ea = 0.16 eV. The increase of the grain size leads to an enhancement of the photoluminescence and, hence, indicates an improvement of the material quality. According to surface photovoltage measurements, the charge-carrier transport length exhibits a linear increase with increasing grain size. The charge-carrier diffusion length is limited by grain boundaries. Moreover, an improved morphology leads to the drastic increase of power conversion efficiency of the devices.