Abstract
Grain boundaries have been established to impact charge transport, recombination and thus the power conversion efficiency of metal halide perovskite thin film solar cells. As a special category of grain boundaries, ferroelastic twin boundaries have been recently discovered to exist in both CH3NH3PbI3 thin films and single crystals. However, their impact on the carrier transport and recombination in perovskites remains unexplored. Here, using the scanning photocurrent microscopy, we find that twin boundaries have negligible influence on the carrier transport across them. Photoluminescence (PL) imaging and the spatial-resolved PL intensity and lifetime scanning confirm the electronically benign nature of the twin boundaries, in striking contrast to regular grain boundaries which block the carrier transport and behave as the non-radiative recombination centers. Finally, the twin-boundary areas are found still easier to degrade than grain interior.
Highlights
Grain boundaries have been established to impact charge transport, recombination and the power conversion efficiency of metal halide perovskite thin film solar cells
Gomez et al claimed these domains in piezoresponse force microscopy (PFM) are ferroelectricity-free by developing direct piezoelectric force microscopy (DPFM) to avoid involving artefacts that might be mistaken as ferroelectric signal in classical PFM, especially for the potential artefacts induced by ion migration, topography crosstalk or charged ions contamination[24]
Solar cells and photodetectors fabricated with these single crystals as photoactive layer already show a high power conversion efficiency (PCE) over 21%31 and an excellent sensitivity with low light detection limit of 0.35 pW cm−2 30, demonstrating the high quality of the single crystals grown by this method
Summary
Grain boundaries have been established to impact charge transport, recombination and the power conversion efficiency of metal halide perovskite thin film solar cells. As a special category of grain boundaries, ferroelastic twin boundaries have been recently discovered to exist in both CH3NH3PbI3 thin films and single crystals Their impact on the carrier transport and recombination in perovskites remains unexplored. TBs are two-dimensional defects, like grain boundaries, but is a special type of 2D defect with no dangling bonds It is still unknown whether TBs would behave like GBs, which has been frequently reported to cause non-radiative charge recombination or blocking carrier transport and decrease the PCE of perovskite solar cells[16]. It is not known yet whether TBs would act as vulnerable sites for external stimuli to induce faster degradation. Understanding the impact of TBs on the charge transport and stability of MHP materials would be of great interests for further increasing the PCE and stability of MHP solar cells
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