Organometallic halide perovskites based photovoltaic (PV) devices are showing revolutionary efficiencies for such a potentially low-cost and low-embodied energy technology with efficiencies exceeding 15%¹ and low temperature manufacturing processes.^1,2 Thus perovskite based PV, with incremental increases in efficiencies and subject to stability, could compete with thin film technologies that require vacuum deposition and expensive non-trivial processing. Aesthetically pleasing coloured organometal halide perovskite cells are also possible though modifying the halide(s) used.³

Here we report the characteristics of a series of methylamine lead halide perovskites with different halides and halide combinations. We have also investigated the effect of lengthening the alkyl chain with the rationale that this may circumvent any possible stability problems towards moisture/humidity. As one might expect, changing the alkyl chain and/or the halide(s) alters the crystal structure and band gap of the perovskite which results in vivid and colourful solar cells; a characteristic which is seen as one of the main benefits of DSC. The band gaps of the synthesised perovskites range from 1.5 – 2.3 eV highlighting the controllability of the optical properties of the organolead halide perovskites. X-ray diffraction and scanning electron microscopy (SEM) with elemental mapping via energy-dispersive x-ray (EDX) analysis has been used to characterise perovskites on sensitised thin films. The smaller ionic radii chloride and bromide halides result in perovskites with larger band gaps and a cubic crystal structure, the iodide based organolead perovskites have a tetragonal crystal structure and have a near-optimum band gap of 1.5 eV. The intermediate band gap iodide/bromide mixtures show a mixed phase crystal structure. Optical microscopy highlights the cubic to tetragonal, through a mixed phase, crystal morphology which correlates well with the XRD data. All the perovskites studied are photovoltaic with efficiencies between 0.5 – 8 % when made under normal laboratory conditions. Coloured perovskite devices made with a transparent conducting laminate back contact which can be specifically used in building integrated PV are detailed. PV device performance and stability is evaluated in relation to the crystal and physical properties of the perovskite and suitability for use in photovoltaic devices is discussed.

References: 

1)Wang, J. T-W.; Ball, J. M.; Barea, E. M.; Abate, A.; Alexander-Webber, J. A.; Huang, J.; Saliba, M.; Mora-Sero, I.; Bisquert, J.; Snaith, H. J.; Nicholas, R. J. Nano Lett. 2014, 14 (2), 724–730.

2)Carnie, M. J.; Charbonneau, C. M. E.; Davies, M. L.; Troughton, J.; Watson, T. M.; Wojciechowski, K.; Snaith, H. J.; Worsley, D. A. Chemical Communications 2013, 49, 7893-7895.

3)Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.; Seok, S. I. Nano Lett. 2013, 13, 1764–9.