Mixtures of quasi-two and three dimensional hybrid organic-inorganic   semiconducting perovskites for single layer LED
  New blends of simply synthesized quasi two-dimensional (quasi-2D) hydrophobic perovskite semiconductors, employed in high performance light emitting diodes (LEDs) which function due to excitonic energy transfer effects, are reported. These materials are self-assembled blends of 2D, quasi-2D and three-dimensional (3D) hybrid organic-inorganic semiconductors (HOIS). Moreover, shown for the first time, crude mixing of 3D perovskite and unprotonated amines provides similar semiconductors. HOIS reported here are based on the organic cations CH3NH3+, CH3(CH2)7CH=CH(CH2)8NH3+ or C6H5CH2CH2NH3+ and inorganic networks formed out of PbX42- anions (X=I, Br, Cl). HOIS exhibit strong bound excitonic states with increased oscillator strength at room temperature, tunable via simple halide substitution. HOIS blends manifest energy transfer effects, where adjacent nanoparticles of different band gap energies (Eg) transfer optical energy to those with the lowest Eg; the suggested light emission mechanism here. LED fabrication is attained via a single deposition of the hydrophobic mixture, reducing device complexity, cost and degradability. LED's diodic behavior is observed even under light albeit its photovoltaic and photoconductive quasi-2D and 3D components. LED devices exposed for over than four months under adverse laboratory conditions, showed stable light emission. Further research on this class of quasi-2D/3D HOIS mixtures is expected to lead to novel quantum electronic devices. 
Anastasia Vassilakopoulou, Dionysios Papadatos, Ioannis Zakouras and   Ioannis Koutselas
cond-mat.mtrl-sci