Abstract
Although photovoltaics employing hybrid perovskite halides have continuously been breaking world- records of power conversion efficiency (PCE) and expectations for their industrialization are rapidly rising, long-term stability issue that has greatly hampered the commercialization of perovskite solar cells has not been resolved yet. Ion instability and trapped charges were suggested as a fundamental reason for perovskite device degradation. Here, we report a pulsatile therapy relieving the accumulation of both trapped charges and ions in the perovskite solar cell device during the middle of maximum power point tracking (MPPT) for reviving the device and prolonging its device lifetime. In the technique, reverse biases are repeatedly applied for a very short time to eliminate the charges accumulated and re-distribute the ions migrated during power harvesting without any pause of operation. Intriguingly, the therapy is not only delaying irreversible degradation, but also, restoring the degraded power right after a short reverse bias. In-situ photoluminescence (PL) and photocurrent (PC) measurements for the working device were done while applying the pulsatile therapy for studying the underlying physics. Time evolving PL intensity and PC not only revealed the steady increase of PL intensity during the therapy indicating the reduction of non-radiative recombination, but also strikingly showed the restoration of degraded PL intensity and PC right after a short reverse bias suggesting the device healing. In the long-term test, we observed outstanding improvement of device stability and total harvesting power. A model considering trap-assisted recombination has also been developed to explain the efficacy of the therapy based on defect formation during MPPT operation and defect healing by the pulsatile therapy. The unique technique will open up new possibility to commercialize perovskite materials into a real market.
Sparkling hot spots in perovskite solar cells under reverse bias
