Incorporating nanostructures in thin film solar cells is an interesting way to improve the optoelectronic performance of the device by means of light-trapping and light management. However, designing the optimal shape and dimensions of the nanostructure is of critical importance for enhanced device performance. It is desired to have synergistic effects in the optical and electronic domains to result in a better performance. However in some nanostructures, the geometrically induced effects in these two domains might counteract resulting in a relatively inferior performance in the nano-structured device. We show this with a simulated example of a nanostructured organic solar cell with nano-pillar transparent electrodes. Here it is seen that the enhancement in photocurrent due to nano-scale scattering through the walls of the pillar is suppressed by the steady-state potential distribution induced by the nano-scale geometry. As a result of poor charge separation in the regions around the pillar, the photocurrents decrease. It is thus highlighted that the opto-electronic transport and electric field enhancement based co-degisn of nanostructures is important to fully understand the nano-scale effects.
This study addresses a unique degradation mechanism in organic electronic devices occurring due to combined effects of electric field and temperature. A simple polymer diode structure consisting of a semiconducting polymer sandwiched between two electrodes (ITO and Al) is considered for degradation studies. It is observed that voltages beyond a certain value lead to fracture of polymer and aluminium films. As characterized, these defects show that the degradation nucleates in the form of a chain-like pattern consisting of alternating polymer fracture sites (hinges) and aluminium rupture sites (links). A mechanism is hypothesized based on experimental observations to explain the phenomenon. This is further validated by an analytical model for stress at degradation sites due to electric field and temperature. The model is used to develop a failure criteria based on device geometry, operating voltage and temperature. Experiments and modelling predict that this mechanism might be unique to soft thin film electronic devices.
Many of the conducting polymers though having good material property are not solution
processable. Hence an alternate method of fabrication of film by pulsed laser deposition, was explored
in this work. PDTCPA, a donor- acceptor- donor type of polymer having absorption from 900 nm to
300 nm was deposited by both UV and IR laser to understand the effect of deposition parameters on the
film quality. It was observed that the laser ablation of PDTCPA doesn’t alter its chemical structure
hence retaining the chemical integrity of the polymer. Microscopic studies of the ablated film shows
that the IR laser ablated films were particulate in nature while UV laser ablated films are deposited as
smooth continuous layer. The morphology of the film influences its electrical characteristics as
current- voltage characteristic of these films shows that films deposited by UV laser are p rectifying
while those by IR laser are more of resistor in nature.