Disclosing the Microscopic Procedures in Perovskite Solar Cells

Now, scientists from Japan have disclosed the physics for how a vital component of a perovskite solar cell works, a study that could result in enhanced solar cells or even newer and better substances. “The main studied have emphasized on enhancing efficacy with perovskite,” says Kazuhiro Marumoto of the University of Tsukuba. “But the microscopic procedure behind how such solar cells using perovskites work has not been completely identified.”

Solar cells function by transforming light energy into electricity. When a photon hits the perovskite, for instance, it knocks an electron loose. The empty spot vacated from the electron is known as hole and functions as a positively charged particle. The subsequent movement of the holes and electrons is what generated electronic current.

Since the perovskite itself does not regulate the movement of holes very well, solar cells need an extra layer of a hole transport substance to facilitate the flow of current. One common hole transport substance is a compound known as spiro-OMeTAD. To augment the current even more, scientists supplemented a lithium salt known as LiTFSI to spiro-OMeTAD. This procedure is known as ‘doping.’

Spiro-OMeTAD is an amorphous substance that delivers some unique properties. Most of the solid substances have well – defined electrical energy bands in which electrons, as well as holes, can move to transport through the substance. Crystals, for instance, often possess band structures that enable for a symmetric flow of both holes and electrons. But amorphous substances do not.

Because of the asymmetric band structure, holes can have an intricate time traveling through an amorphous substance as they can get trapped in a specific energy level. But, according to the theory, doping spiro-OMeTAD with LiTFSI prevents the trapping of holes.

Couples of electrons occupy each energy level in spiro-OMeTAD. But when LiTFSI is introduced, one of such electrons is eradicated, leaving behind a hole in its place. The presence of such hole prevents other holes from getting stuck as such high energy level, enabling them to move freely and produce electrical current.

Conventionally, no one has confirmed this procedure. But Marumoto and his team members have now employed spin resonance spectroscopy to reveal that this mechanism is responsible for enhancing the potential of spiro-OMeTAD to supply current.

ESR spectroscopy identifies the spin of single, unpaired electrons that is what is prepared when spiro-OMeTAD is doped with LiTFSI. In studies without light, the scientists identified that the number of electron spins in spiro-OMeTAD augmented by two orders of magnitude after getting doped. To identify how doping affects the efficacy of a perovskite OMeTAD solar cells, the scientists then performed their studies on the two substances layered together with the lights on.