Using Solar Simulator light-dependent-techniques to analyze bi-molecule recombination in OPV.
Recently, L. Zhong et al. demonstrate highly efficient ternary norfullerene OPV with two polymer donors and an organic acceptor. The results indicate that adding proper amount (20%) PTB7-Th polymer in the polymer donor could effectively improve in the ternary OPVs.
To illustrate the increasing of is due to the suppression of bimolecular recombination by PTB7-Th, they used light-dependent techniques to measure the dependence of on the illumination intensity of the solar simulator. In the following, we will shortly describe this technique.
It is already a general consensus that bi-molecule recombination is the most important recombination channel in current BHJ OPVs, controlling the J-V curve and limiting Voc and FFs. (Ref1)
Experimental studies of recombination have been effectively controls J-V characteristics of the devices. These allow for a thorough analysis of where losses are occurring within a device, based on just a simple J-V measurement. The follows the power-law dependence versu light intensity, which can be expressed as . In general, when equal to 1, bimolecular recombination can be neglected*. (Ref. 2)
Koster and colleagues (Ref2) studied Jsc as a function of light intensity (I) for annealed P3HT: PCBM devices at different temperatures. The follows the power-law:L. Zhong et al. also adopted the same methodology to prove the Jsc increasing in ternary devices is coming from the suppression of bimolecular recombination compared to binary devices.
From Schottky equation it is easy to derive that
Z. Song, A. Abate, S. C. Watthage, G. K. Liyanage, A. B. Phillips, U. Steiner, M. Graetzel, M. J. Heben Perovskite Solar Cell Stability in Humid Air: Partially Reversible Phase Transitions in the PbI2-CH3NH3I-H2O System. Advanced Energy Materials 2016, 1600846