We report the use of ultra-sonic spray-coating under ambient conditions as a deposition technique for the fabrication of planar heterojunction CH₃NH₃PbI_3−xCl_x perovskite solar cells. We make a first optimization of processing parameter space using this deposition technique, and explore the role of the temperature of the substrate during spray-casting, the volatility of the casting solvent and the post deposition anneal on determining the efficiency of the resultant solar cells. We find that maximum device efficiency is correlated with the creation of dense films having a surface coverage above 85%. When such films are incorporated into a solar cell device, power conversion efficiencies of up to 11% are realized. These results demonstrate that spray-coating can be used in the large-area, low-cost manufacture of high efficiency solution-processed perovskite solar cells.

Current–voltage, impedance, and transient conductance measurements have been carried out on indium-tin-oxide/poly(phenylene vinylene)/Al light emitting diodes. In these devices injection and transport is expected to be dominated by positive carriers. Fowler–Nordheim tunneling theory cannot account for the temperature dependence, the thickness dependence, or the current magnitude of the current–voltage characteristics. Space-charge limited current theory with an exponential distribution of traps is however in extremely good agreement with all of the recorded current–voltage results in the higher applied bias regime (approximately ${\text{0.7⩽V/d⩽1.6×10}}^6\hspace{0.17em}{\mathrm{V\hspace{0.17em}cm}}^{\mathrm{-1}}$ ). This gives a trap density $H_t$ of ${\text{5(±2)×10}}^{17}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-3}}$ and the product of ${\mathrm{\mu N}}_{\mathrm{HOMO}}$ of between ${10}^{14}$ and ${\text{5×10}}^{12}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-1}}{\mathrm{\hspace{0.17em}V}}^{\mathrm{-1}}{\mathrm{\hspace{0.17em}s}}^{\mathrm{-1}}.$ Assuming $N_{\mathrm{HOMO}}$ is ${10}^{20}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-3}}$ gives an effective positive carrier mobility between ${10}^{\text{−6}}$ and ${\text{5×10}}^{\text{−8}}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{2}}{\mathrm{\hspace{0.17em}V}}^{\mathrm{-1}}{\mathrm{\hspace{0.17em}s}}^{\mathrm{-1}}.$ The characteristic energy $E_t$ of the exponential trap distribution is 0.15 eV at higher temperatures $\text{(190⩽T⩽290\hspace{0.17em}}\mathrm{K}\mathrm{),}$ but this decreases as the devices are cooled, indicating that the distribution is in fact a much steeper function of energy closer to the highest occupied molecular orbital (HOMO) levels. The current–voltage characteristics in the lower applied bias regime (approximately ${\text{V/d⩽0.7×10}}^6\hspace{0.17em}{\mathrm{V\hspace{0.17em}cm}}^{\mathrm{-1}}$ ) can be fitted to pure space-charge limited current flow with a temperature and field dependent mobility of Arrhnenius form with a mobility at 290 K close to the above values. If $N_{\mathrm{HOMO}}$ lies between ${10}^{21}$ and ${10}^{19}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-3}},$ then the trap filled limit bias gives a mobility independent value of $H_t$ of ${\text{3(±1)×10}}^{17}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-3}}.$ Capacitance–voltage measurements show that at zero bias the devices are fully depleted, and that the acceptor dopant density $N_A$ must be less than about ${10}^{16}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-3}}.$ The impedance results show that the devices can be modeled on a single, frequency independent, parallel resistor-capacitor circuit with a small series resistor. The variation of the resistor and capacitor in the parallel circuit with applied bias and temperature are consistent with the space-charge limited current theory with the same exponential trap distribution used to model the current–voltage characteristics. Initial results for transient conductance measurements are reported. The transients have decay times greater than 300 s and exhibit a power-law dependence with time. This is shown to be exactly the behavior expected for the decay of an exponential trap distribution. Measurements at higher temperatures $\text{(290⩾T⩾150\hspace{0.17em}}\mathrm{K})$ give an $E_t$ of 0.15 eV, in excellent agreement with that found from the current–voltage measurements. This value of $E_t$ is exactly that found by similar analysis of the current–voltage characteristics in negative carrier dominated dialkoxy poly(phenylene vinylene) and ${\mathrm{Mq}}_3$ devices. It is proposed that this bulk transport dominated behavior is purely a consequence of hopping conduction through an approximately Gaussian density of states in which the deep sites act as traps.

Many organic materials (disordered and crystalline as well) have rather broad and dispersionless electronic resonances. The excitations in these materials are localized, and thus for these excitations the wave vector is not a “good” quantum number. We analyze the optical properties of exciton polaritons in a microcavity, which utilize such organic materials as the optically active semiconductor. We show that as a result of strong light-matter coupling two polariton branches appear in the microcavity, which are analogous to the cavity-polariton branches observed in inorganic semiconductor structures. However, in contrast to the case of polaritons in inorganic semiconductors, the lower polariton branch exists only in a certain restricted intervals of wave vector values. We also show that in such materials the majority of the electronic excited states do not strongly couple to the cavity photon, and these states can be regarded as essentially incoherent. Applying this physical picture for the microcavities containing disordered cyanine dye J aggregates, we examine the decay of the upper cavity polaritons accompanied by the emission of an intramolecular phonon. We show that the main contribution to the upper polariton nonradiative decay rate arises from the transition to incoherent states, and the transition is very fast (of the order of 50 fs). From the results of our calculations we discuss the dynamics of excitations in a microcavity containing organic materials

We report a room temperature study of the strong exciton-photon coupling regime in a planar microcavity, containing cyanine dye aggregates with delocalized exciton wave functions ( $J$ aggregates). Giant Rabi splittings of 80 meV between upper and lower polariton branches are observed and cavity polariton emission is detected from the lower polariton branch. The small linewidth and large oscillator strength characteristic of $J$ aggregates make them a favorable physical structure to allow the observation of strong coupling for organic semiconductors.