SUBAIR, Riyas – GIROLAMOC, Diego Di – BODIK, Michal – NÁDAŽDY, Vojtech – LI, Bo – NÁDAŽDY, Peter – MARKOVIČ, Zoran – BENKOVIČOVÁ, Monika – CHLPÍK, Juraj – KOTLÁR, Mário – HALAHOVETS, Yurily – ŠIFFALOVIČ, Peter – JERGEL, Matej – TIANE, Jianjun – BRUNETTI, Francesca – MAJKOVÁ, Eva
In Solar Energy. Vol. 189, (2019)
https://doi.org/10.1016/j.solener.2019.07.088
Abstract
The doping effect of carbon nanodots (CNDs) in the PC61BM electron-transport layer on the performance of inverted planar MAPbI3 perovskite solar cells (PSCs) having two different kinds of the hole-transport layer, namely organic PEDOT:PSS and inorganic NiOx, was investigated. The CH3NH3PbI3 perovskite layer was deposited in air at 35% humidity. An average 11% and 12% enhancement of the power conversion efficiency (PCE) was achieved for 1 wt% CNDs doping in the PSCs with PEDOT:PSS and NiOx, respectively. This improvement is attributed to high electron density of CNDs resulting in a triple increase of the electrical conductivity of the PC61BM layer and passivation of the perovskite/PC61BM interface that is reflected by an increase of the open-circuit voltage. In line with this, parallel resistance and fill factor of the PSCs are also improved. Moreover, the energy-resolved electrochemical impedance spectroscopy revealed additional free-charge carriers in the PC61BM layer generated under illumination that were detected via the polaron states formation in the band gap with positive effect on the short-circuit current. All these factors contribute to the PCE improvement. Stability tests of the PSC with PEDOT:PSS under a continuous 24 hour 1.5 AM illumination showed a five times smaller final PCE decrease for the 1 wt% CNDs doping of the PC61BM layer comparing to the undoped counterpart. The passivation effect of CNDs, namely electron filling the traps formed by the photo-dimerization and photo-oxidation of PC61BM molecules, is responsible for this remarkable improvement of the short-term stability.