Lorenzo Torto

Effects of current stress and thermal storage on polymeric heterojunction P3HT:PCBM solar cell

We subjected P3HT:PCBM solar cells to electrical constant current stress and thermal storage. We employed the impedance spectroscopy technique combined to conventional DC measurements for device characterization during all stresses. We identified and separated different contributions affecting the open circuit voltage and short circuit current. Several mechanisms are behind these changes during the stresses; in particular, we underlined the exciton recombination rate and the variation of the built-in voltage.

Application of Photocurrent Model on Polymer Solar Cells Under Forward Bias Stress

We performed a constant current stress at forward bias on organic heterojunction solar cells. We measured current voltage curves in both dark and light at each stress step to calculate the photocurrent. An existing model applied to photocurrent experimental data allows the estimation of several parameters such as generation, recombination, dissociation rate, and nearly zero field voltage within the active layer as a function of the stress time. The analysis of extrapolated parameters shows that the stress mainly affects the recombination rate of the polaron charge transfer states.

Analysis of electrical and thermal stress effects on PCBM:P3HT solar cells by photocurrent and impedance spectroscopy modeling

We investigated the effects of electrical stress and thermal storage by means of photocurrent, Impedance Spectroscopy and Open Circuit Voltage Decay models. The electrical stress damages only the active layer, by reducing the generation rate, the polaron separation probability and the carrier lifetime. The thermal stress also degrades the anode interface. This reflects on the appearance of an inflection in the I-V photocurrent shape close to the operative region.

Open circuit voltage decay as a tool to assess the reliability of organic solar cells: P3HT:PCBM vs. HBG1:PCBM

We developed a model that explain the open circuit voltage decay in polymeric solar cells to analyze the effects of the degradation induced by accelerated life-tests. The model accounts for the polaron pairs separation and recombination, the Langevin recombination, and the trap assisted recombination. The model permits to calculate several parameters. Among them, for the first time, we were able to extrapolate the Energy Gap of the blend from electrical, non-destructive measurements. We performed electrical stresses on organic solar cells based on two different active layers (P3HT:PC61BM, HBG1:PC61BM) applying specific characterizations, including open circuit voltage decay. We showed the better reliability of HBG1 based devices with respect to the analogous systems containing P3HT as donor material.

Effects of thermal stress on hybrid perovskite solar cells with different encapsulation techniques

We subjected to both storage and thermal stress solid state solar cells based on organometal perovskites and using Spiro-OMeTAD as hole transport material. We applied two different sealing techniques to encapsulate the devices, in order to study the differences during the experiment. Applying both fast ciclo-voltammetry, transient measurement and very slow DC measurements, we correlated the results obtained during the 540h experiment to different degradation dynamics within the cell structure. The correlation allows us to distinguish at least two possible sources of degradation that can help understand loss mechanisms of perovskite solar cells.