Perovskite as an effective V_oc switcher for high efficiency polymer solar cells

In the perovskite/polymer based parallel-like tandem solar cell, the distinctive absorption spectra between the organic-inorganic halide perovskite absorber (CH₃NH₃PbI₃ (MAPI)) and poly-(diketopyrrolopyrrole-terthiophene) (PDPP3T) polymer absorber make it possible to investigate the electronic properties of charge carriers generated in either the perovskite or PDPP3T layer separately. The current density-voltage (J-V) curves of the device are measured under the monochromatic LED irradiation at significantly different wavelengths to confirm the charge carrier generated in MAPI offer higher V_oc. The voltage biased external quantum efficiency (EQE) measurement is employed to understand the charge transport mechanism in the system. The J-V curves and EQE data confirm that charge carriers generated by the photons absorbed in the perovskite layer or in PDPP3T behave independently. Compared with the bulk heterojunction structure, this parallel-like tandem structure increases V_oc while reducing thermalization loss, providing a possibility to break the traditional Shockley-Queisser (S-Q) limit set for single junction devices.