Solution-processed organic-inorganic hybrid perovskite solar cells have been at the forefront of global photovoltaic research. Considering the immense potential these materials possess due to their enhanced photophysical properties, and the rapid enhancement in power conversion efficiency, it is on the right path to replace the present silicon solar cell technology.

In light of the ongoing research in the field of perovskite devices, our group developed a new crystal growth technique, namely solution based Hot-Casting technique, which allows the growth of millimeter-scale crystalline grains for highly efficient and reproducible thin film solar cells (see Nie et al. Science 347, 6221, pp. 522-525, 2015). We fabricated planar solar cells with efficiencies approaching 18%, which is among the highest reported in the field of perovskite-based light-to-energy conversion devices. In this work, we also demonstrated in-depth how large-grain perovskite benefits photovoltaics. Specifically, we showed that large-grain perovskite has very low defect density as compared to smaller grains (<10 um) using time-resolved photoluminescence (time-correlated single-photon counting).

Developing and understanding novel strategies for improving the performance of perovskite-based devices

The perovskite materials are all set to dominate the field of thin-film optoelectronic devices. But one of the primary challenges is the processing-dependent variability of the photophysical properties, making understanding the origin of such variations imperative. Our group discovered that the precursor solution aging time before being cast into a thin film is a  very important factor that dramatically affects the overall thin-film formation and crystallinity, and therein factors such as grain growth, phase purity, surface uniformity, trap state density, and overall solar cell performance (see Tsai et al. Advanced Energy Materials 7 (11), 1602159, 2017).

For further understanding, we studied the growth of hybrid perovskite films on the newly emerging hole transporting layer (i.e. Nickel oxide (NiO)) to study the correlation between the degree of crystallinity of the fabricated films on the device performance and photostability. Specifically, we showed a reduced trap density at the perovskite/NiO interface using Photophysical and interface-sensitive measurements, leading to enhanced performance and increased photostability of the photovoltaic devices (see Nie et al. Advanced Materials 30 (5), 1703879, (2018)).

Deterministic fabrication of 3D/2D perovskite bilayer stacks for durable and efficient solar cells

Although 3D perovskites have amazing optoelectronic properties that enable >25% PCE, they are still fragile to the ambient atmosphere (Oxygen, Light, Humidity). This makes their commercialization difficult. 2D perovskites, on the other hand, have shown remarkable stability when compared to 3D perovskites, but their worse charge transport properties limit their use as standalone PV devices. Siraj et al. developed a novel method to deposit a 2D perovskite on 3D perovskite using a solvent that preferentially dissolves 2D perovskite, not 3D perovskite. This method improves the interface between the 3D-2D and the transport layer and the stability under MPP tracking conditions to a t99>2000h. (Sidhik et al. SCIENCE, 22 Sep 2022, Vol 377, Issue 6613)