| Abstract [eng] |
Introduction to organic photovoltaics with more detailed outlook on efficiency and carrier dynamics in organic solar cells was presented in first part of this work. As well basic information about transient photocurrent, time-delayed collection field and TREFISH measurement techniques, mathematics of photocurrent simulation, materials and devices utilized in this work were introduced. Following work has showed that carrier density kinetics within normal working conditions of all-polymer solar cell is mostly determined by recombination rather than extraction during initial few μs time frame. However, carrier density plays minor part determining photocurrent kinetics, while it is mostly conditioned by decreasing mobility, as integrated photocurrent simulation revealed. Most of photo induced charge carrier are being spatially, rather than energetically, trapped during their drift. Spatial traps are attributed to dead end's of long polymer chains, number of which can be drastically reduced by thermal annealing and is inherently smaller in polymer/fullerene system. The impact of trapping due to bended HOMO/LUMO energy levels in vicinity of electrodes is marginal for charge extraction. Whereas impact of one sun background lighting was found to be significant in polymer/fullerene systems. Photocarriers generated by constant light occupies lowest energy states and consequently alters laser induced photocurrent dynamics in microsecond time scale. Such alteration is not observed in sub-nanosecond time frame, when carrier relaxation within DoS is taking place. |
