What caused the perovskite solar cell to have a low Voc? I know that poor cells exhibit low FF due to pinholes presence on the light absorbing layer, causing the short circuit between gold contact/HTM with ETL (TiO2 layer), but what about the Voc? What caused the cell to have low Voc?
The pervoskite solar cells follow fairly the one diode model of the conventional solar cells which means that the opencircuit voltage can be expressed by Voc= nVt Ln(Iph/is) with N the ideality factor, Vt the thermal voltage , Iph is the short circuit current and Is is the reverse saturation current. So, low Voc may be due to:
- too low photocurrent, which may not be the case for good absorbing materials like the pervoskites,However. the generated electron holes may not be effectively collected. They may recombine before the disposal by the built in electric field.
- Too large reverse saturation current because of the high recombination rate in the pervoskite and at the interface of the HTL and the ETL since these are heterofaces with defects.
However, some deficiencies which you mentioned in your question can lead also to smaller Voc. Specifically the pinholes filled with metals that create shortcircuits from the andode to cathode. It is known that as the short circuit resistance decreases, the open circuit voltage decreases and also the fillfactor as i-v curve will resemble a triangle.
Thank you very much for the elaborated answer Prof Abdel Halim. Does the thicker layer of mp-TiO2 + perovskite also give rise to this low Voc?
From y experience a thinner layer of bothd compact and mesoporous layer can enhance the Voc
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