Both bismuth and copper are non-toxic and earth-abundant elements suitable for lead-free halide perovskite-like photovoltaic devices. Here, we report a highly facile route for in-situ producing copper-bismuth-iodide (CuBiI 4 ) thin films directly on ITO substrate at room temperature, by utilizing a Bi-Cu alloy layer as precursor. X-ray diffraction and transmission electron microscopy (TEM) results verified the formation of well crystallized CuBiI 4 thin films with [222] orientation. The transient photovoltage (TPV) analysis revealed that the CuBiI 4 is an n-type semiconductor with a suitable band gap of ~1.81 eV, preferable to photoelectric conversion compared with CH 3 NH 3 PbI 3 . It is very interesting that the subsequent spin-coating process of the classical Spiro-MeOTAD organic solution with TBP and acetonitrile resulted in a dense and smooth CuBiI 4 :Spiro-MeOTAD bulk-heterojunction film. The preliminarily fabricated simple sandwich structures of ITO/CuBiI 4 :Spiro-MeOTAD/Au hybrid solar cell devices displayed efficient photovoltaic performance with the PCE up to 1.119% of the best sample. The room temperature direct metal surface elemental reaction (DMSER) method may provide a new insight for all-inorganic lead free perovskite-like A a B b X x compounds and high performance photovoltaic devices.
Designing lead-free inorganic perovskite or perovskite-like structure materials and researching the corresponding photoinduced charge carrier dynamics are always promising due to both the environment and power conversion efficiency considerations. In this work, we intelligently employ a bilayer metal Bi/Cu thin film with different atomic ratios as the precursor to fabricate a CuBiI4 perovskite-like film in situ with a controlled Bi gradient at room temperature. This structure can significantly affect the photoinduced charge carrier dynamics of the resulting products. Next, a series of transient surface photovoltage (TSPV) measurements are carried out to investigate the photoinduced charge carrier dynamics of such CuBiI4 and CuBiI4:organic hybrid thin films. The results reveal that the gradually decreasing Bi content from ITO to CuBiI4 can facilitate the photoinduced charge carrier transportation. Finally, a champion PCE of 1.10% is obtained for an ITO/CuBiI4:polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7)/Au solar cell device. In particular, we find an exact negative correlation of the defined parameter L (the defined value for evaluating the photoinduced charge carrier dynamics in TSPV measurements) with the corresponding PCE of various devices for the first time, which may pave a new way for evaluating the potential photoelectric and photovoltaic performances of new materials without the assembly of solar cell devices.
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