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We investigate the role of n-type organic molecule, bathocuproine (BCP), additive in perovskite semiconductor film based solar cells using first principle calculations and optoelectronic studies. A state-of-art high fill factor of 0.82 and improved open circuit voltage of 0.95 V for CH3NH3PbI3 (MAPI) based perovskite solar cells are achieved in addition with highly improved (more than one order) electroluminescence efficiency. Delayed emission spectroscopy does not show any blue shift peak or double peak emission suggests no structural changes in 3D perovskite. Contact angle studies using water droplet supports BCP is forming a capping layer to boost moisture barrier. Our experimental findings regarding no 2D structure formation has also been supported by first-principles electronic structure calculations based on DFT in MAPI after insertion of BCP. Furthermore, calculations suggest that a physisorption type of interaction has been found in between MAPI and BCP with an average distance of 2.9 A. These res...

The photoluminescence (PL) decay of hybrid halide perovskite single crystals (MAPbX(3), MA = CH3NH3+, Pb = Pb2+, X = Br-, and I-) is measured over 4 orders of magnitude in intensity over the time scales of 100s of nanoseconds to a few microseconds. This long PL decay is non-exponential, suggesting the presence of a distribution of carrier relaxation times. Spectro-temporal studies show that the emission peak red-shifts with increasing time. The physics of this problem is closely related to donor-acceptor pair recombination in crystalline semiconductors and recombination in a-Si:H. Based on these models, we present a simple model to account for the recombination dynamics in the perovskite systems. This model also accounts for the fluence dependence of the recombination kinetics. In this model, a fraction of the photogenerated electrons and holes are trapped in localized states. The electrons tunnel to the hole sites for recombination. The broad distribution of lifetimes is a consequence of the fact that the tunneling probability is very sensitive to the separation of electron-hole pairs, and PL decay dynamics is a function of excitation fluence, i.e., carrier density generated by optical excitation. The red-shift arises from the fact that holes and electrons are trapped at different energies.

Photocarrier generation mechanisms in 3,6-diaryl-N-hexylcarbazole (aryl = p-cyanophenyl and p-acetophenyl) were studied in single-layer, bilayer, and blend film devices in sandwich geometry between...

In this paper, we report on an integrated OLED― photodetector organic device using 3,6-dipyrenyl-N-hexylcarbazole (P2NHC) as the active layer. This device is an efficient blue emitter in forward bias and an efficient visible-blind UV photodetector in reverse bias. In forward bias, the device (as a blue emitter) has a low turn on voltage (2.7 V), a current efficiency of 2.0 cd/A for a brightness of 200-9000 cd/m 2 , and low droop at higher brightness. In reverse bias, the device has a saturated photoresponse of 77 mA/W at 390 nm, which corresponds to an internal quantum efficiency of 64%. The spectral response of a photodetector-only device indicated that carriers are generated in the interface of P2NHC/cathode. The singlet exciton diffusion length of P2NHC was determined to be 7.8 ± 1 nm, which is too small to account for the high photodetector efficiency. Alternate mechanisms are discussed to account for the high photodetector efficiency.