Band Gap Tuning of Organic-Inorganic Metal Halide Perovskites for Photovoltaics

As a result of the tremendous research efforts across the world, hybrid organic-inorganic metal halide perovskite based solar cells are now comparable to other previously existing high efficient technologies with power conversion efficiency exceeding 20%. The existence of intrinsic and extrinsic instability in these materials remains a major challenge to commercialization of the solar cells. However, mixed halides are expected to solve instability problems. Here we investigate experimentally the effect of halogen on the structural, electronic and optical properties of mixed halide MAPb(I_1-xBr_x)₃, MAPb(I_1-xCl_x)₃ and MAPb(Br_1-xCl_x)₃ perovskites. Single-step deposition method with the application of doctor blade coating is used to fabricate perovskite thin films on glass substrates. As the Br and Cl contents ‘x’ increase from 0.0 to 1.0, the band gap energy increases as a linear function. The photo-absorption coefficients are calculated showing blue-shift of the absorption onsets for higher Br or Cl concentrations. We also investigate a systematic long term stability of these materials in ambient atmosphere.