The maximum efficiency of any solar cell can be evaluated in terms of its corresponding ability to emit light. We herein determine the important figure of merit of radiative efficiency for Methylammonium Lead Iodide perovskite solar cells and, to put in context, relate it to an organic photovoltaic (OPV) model device. We evaluate the reciprocity relation between electroluminescence and photovoltaic quantum efficiency and conclude that the emission from the perovskite devices is dominated by a sharp band-to-band transition that has a radiative efficiency much higher than that of an average OPV device. As a consequence, the perovskite have the benefit of retaining an open circuit voltage ~0.14 V closer to its radiative limit than the OPV cell. Additionally, and in contrast to OPVs, we show that the photoluminescence of the perovskite solar cell is substantially quenched under short circuit conditions in accordance with how an ideal photovoltaic cell should operate.

We investigated the influence of oxygen on the performance of P3HT:PCBM (poly(3hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester) solar cells by current-voltage, thermally stimulated current (TSC) and charge extraction by linearly increasing voltage (CELIV) measurement techniques. The exposure to oxygen leads to an enhanced charge carrier concentration and a decreased charge carrier mobility. Further, an enhanced formation of deeper traps was observed, although the overall density of traps was found to be unaffected upon oxygen exposure. With the aid of macroscopic simulations, based on solving the differential equation system of Poisson, continuity and drift-diffusion equations in one dimension, we demonstrate the influence of a reduced charge carrier mobility and an increased charge carrier density on the main solar cell parameters, consistent with experimental findings.

Adding cesium (Cs) and rubidium (Rb) cations to FA0.83MA0.17Pb(I0.83Br0.17)3 hybrid lead halide perovskites results in a remarkable improvement in solar cell performance, but the origin of the enhancement has not been fully understood yet. In this work, Time-of-Flight (ToF), Time-Resolved Microwave Conductivity (TRMC), and Thermally Stimulated Current (TSC) measurements were performed to elucidate the impact of the inorganic cation additives on the trap landscape and charge transport properties within perovskite solar cells. These complementary techniques allow for the assessment of both local features within the perovskite crystals and macroscopic properties of films and full devices. Strikingly, Cs-incorporation was shown to reduce the trap density and charge recombination rates in the perovskite layer. This is consistent with the significant improvements in the open-circuit voltage and fill factor of Cscontaining devices. By comparison, Rb-addition results in an increased charge carrier mobility, which is accompanied by a minor increase in device efficiency and reduced current-voltage hysteresis. By mixing Cs and Rb in quadruple cation (Cs-Rb-FA-MA) perovskites, the advantages of both inorganic cations can be combined. Our study provides valuable insights into the role of these additives in multiple-cation perovskite solar cells, which are essential for the design of highperformance devices.

Thermally stimulated current (TSC) measurements are used to characterize electronic trap states in methylammonium lead iodide perovsite solar cells. Several TSC peaks were observed over the temperature range from 20 K to room temperature. To elucidate the origins of these peaks, devices with various organic charge transport layers and devices without transport layers were tested. Two peaks appear at very low temperatures, indicating shallow trap states that are mainly attributed to the PCBM/C60 electron transport bilayer. However, two additional peaks appear at higher temperatures, that is, they are deeper in energy, and are assigned to the perovskite layer. At around T = 163 K, a sharp peak, also present in the dark TSC measurements, is assigned to the orthorhombic-tetragonal phase transition in the perovskite. However, a peak at around T = 191 K is assigned to trap states with activation energies of around 500 meV but with a rather low concentration of 1 × 10(21) m(-3).

The trap distribution in the conjugated polymer poly(3-hexylthiophene) was investigated by fractional thermally stimulated current measurements. Two defect states with activation energies of about 50 meV and 105 meV and Gaussian energy distributions were revealed. The first is assigned to the tail of the intrinsic density of states, whereas the concentration of second trap is directly related to oxygen exposure. The impact of the oxygen induced traps on the charge transport was examined by performing photo-induced charge carrier extraction by linearly increasing voltage measurements, that exhibited a strong decrease in the mobility with air exposure time.Conjugated polymers are grown in interest for application in organic electronic devices such as organic light emitting diodes (OLEDs), field effect transistors and solar cells, due to their low cost processability from solution phase. The presence of traps can be critical to the performance of these devices since they reduce the charge carrier mobility, affect the driving voltage, disturb the internal field distribution and reduce the operation stability as well as the electroluminescence efficiency [1]. Concerning the lifetime of the devices, the influence of oxygen-related defect states on the charge transport might be decisive with respect to the long-term stability. In this work we investigated the trap distribution in poly(3-hexylthiophene) (P3HT) by a fractional thermally stimulated current technique. Furthermore the influence of oxygen on the trap states and their impact on the charge carrier mobility were examined. Diodes with the sandwich structure indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/ P3HT/Al were fabricated in nitrogen atmosphere. P3HT was spincoated on PEDOT:PSS covered ITO glass substrate, from 2 wt% chlorobenzene solution at 800 rpm for 60 s, resulting in a film thickness of 220 nm. The 100 nm thick Al electrodes were thermally deposited at a deposition rate of 0.7 nm/s. Thermally stimulated current (TSC) and photocharge extraction by linearly increasing voltage (photo-CELIV) measurements [2,3] were performed in a closed cycle cryostate (Janis CCS 550) with He atmosphere as contact gas. During the transfer to the cryostate, the samples were exposed to air for about five minutes. To optain the TSC spectra the samples were cooled down to 28 K. Trap filling was achieved by illumination of the samples with a 150 W halogen lamp for five minutes, since longer excitation times did not show an increase in the TSC signal. After a dwell time * Electronic mail: julia.schafferhans@physik.uni-wuerzburg.de † Electronic mail: dyakonov@physik.uni-wuerzburg.de of also five minutes the temperature was increased with a constant heating rate of 7 K/min up to 300 K. During the measurements no external electric field was applied to avoid an overlap of the thermally stimulated and injection current, implying that the detrapped charge carriers were extracted from the sample only due to the built-in voltage, given by th...