Anand S. Subbiah

If perovskite solar cells (PSCs) with high power conversion efficiencies (PCEs) are to be commercialized, they must achieve long-term stability, which is usually assessed with accelerated degradation tests. One of the persistent obstacles for PSCs has been successfully passing the damp-heat test (85°C and 85% relative humidity), which is the standard for verifying the stability of commercial photovoltaic (PV) modules. We fabricated damp heat-stable PSCs by tailoring the dimensional fragments of two-dimensional perovskite layers formed at room temperature with oleylammonium iodide molecules; these layers passivate the perovskite surface at the electron-selective contact. The resulting inverted PSCs deliver a 24.3% PCE and retain >95% of their initial value after >1000 hours at damp-heat test conditions, thereby meeting one of the critical industrial stability standards for PV modules.

We report on bulk-heterojunction (BHJ) organic photovoltaics (OPVs) based on the self-assembled monolayer (SAM) 2PACz as a hole-selective interlayer functionalized directly onto the indium tin oxide (ITO) anode. The 2PACz is found to change the work function of ITO while simultaneously affecting the morphology of the BHJ deposited atop. Cells with PM6:N3 BHJ and ITO-2PACz anode exhibit a power conversion efficiency (PCE) of 16.6%, which is greater than that measured for bare ITO (6.45%) and ITO/PEDOT:PSS (15.94%) based devices. The enhanced performance is attributed to lower contact-resistance, reduced bimolecular recombination losses, and improved charge transport within the BHJ. Importantly, the ITO-2PACz-based OPVs show dramatically improved operational stability when compared with PEDOT:PSS-based cells. When the ITO-2PACz anode is combined with the ternary PM6:BTP-eC9:PC71BM BHJ, the resulting cells exhibit a maximum PCE of 18.03%, highlighting the potential of engineered SAMs for use in hole-selective contacts in high-performance OPVs.

The performance of perovskite solar cells with inverted polarity (p-i-n) is still limited by recombination at their electron extraction interface, which also lowers the power conversion efficiency (PCE) of p-i-n perovskite-silicon tandem solar cells. A MgF x interlayer with thickness of ~1 nanometer at the perovskite/C 60 interface favorably adjusts the surface energy of the perovskite layer through thermal evaporation, which facilitates efficient electron extraction and displaces C 60 from the perovskite surface to mitigate nonradiative recombination. These effects enable a champion open-circuit voltage of 1.92 volts, an improved fill factor of 80.7%, and an independently certified stabilized PCE of 29.3% for a monolithic perovskite-silicon tandem solar cell ~1 square centimeter in area. The tandem retained ~95% of its initial performance after damp-heat testing (85°C at 85% relative humidity) for >1000 hours.

Hybrid organic-inorganic semiconducting perovskite photovoltaic cells are usually coupled with organic hole conductors. Here, we report planar, inverse CH3NH3PbI3-xClx-based cells with inorganic hole conductors. Using electrodeposited NiO as hole conductor, we have achieved a power conversion efficiency of 7.3%. The maximum VOC obtained was 935 mV with an average VOC value being 785 mV. Preliminary results for similar cells using electrodeposited CuSCN as hole conductor resulted in devices up to 3.8% in efficiency. The ability to obtain promising cells using NiO and CuSCN expands the presently rather limited range of available hole conductors for perovskite cells.