Hak-Beom Kim

Boosting the Power Conversion Efficiency of Perovskite Solar Cells Using Self‐Organized Polymeric Hole Extraction Layers with High Work Function

A self-organized hole extraction layer (SOHEL) with high work function (WF) is designed for energy level alignment with the ionization potential level of CH3 NH3 PbI3 . The SOHEL increases the built-in potential, photocurrent, and power conversion efficiency (PCE) of CH3 NH3 PbI3 perovskite solar cells. Thus, interface engineering of the positive electrode of solution-processed planar heterojunction solar cells using a high-WF SOHEL is a very effective way to achieve high device efficiency (PCE = 11.7% on glass).

Conjugated polyelectrolyte hole transport layer for inverted-type perovskite solar cells

Organic–inorganic hybrid perovskite materials offer the potential for realization of low-cost and flexible next-generation solar cells fabricated by low-temperature solution processing. Although efficiencies of perovskite solar cells have dramatically improved up to 19% within the past 5 years, there is still considerable room for further improvement in device efficiency and stability through development of novel materials and device architectures. Here we demonstrate that inverted-type perovskite solar cells with pH-neutral and low-temperature solution-processable conjugated polyelectrolyte as the hole transport layer (instead of acidic PEDOT:PSS) exhibit a device efficiency of over 12% and improved device stability in air. As an alternative to PEDOT:PSS, this work is the first report on the use of an organic hole transport material that enables the formation of uniform perovskite films with complete surface coverage and the demonstration of efficient, stable perovskite/fullerene planar heterojunction solar cells.

An Organic Surface Modifier to Produce a High Work Function Transparent Electrode for High Performance Polymer Solar Cells

Modification of an ITO electrode with small-molecule organic surface modifier, 4-chloro-benzoic acid (CBA), via a simple spin-coating method produces a high-work-function electrode with high transparency and a hydrophobic surface. As an alternative to PEDOT:PSS, CBA modification achieves efficiency enhancement up to 8.5%, which is attributed to enhanced light absorption within the active layer and smooth hole transport from the active layer to the anode.

Inverted Colloidal Quantum Dot Solar Cells

An inverted architecture of quantum dot solar cells is demonstrated by introducing a novel ZnO method on top of the PbS CQD film. Improvements in device characteristics stem from constructive optical interference from the ZnO layer that enhances absorption in the PbS CQD layer. Outstanding diode characteristics arising from a superior PbS/ZnO junction provide a further electronic advantage.

Replacing the metal oxide layer with a polymer surface modifier for high-performance inverted polymer solar cells

Replacing ZnO with PEIE, both as a surface modifier for the low work function electrode and as an electron selective layer, enhances the performance and air stability of inverted polymer solar cells by improving electron transport, wettability between the active layer and the cathode, and maximizing light absorption within the active layer without light interference.

Effects of Ionic Liquid Molecules in Hybrid PbS Quantum Dot–Organic Solar Cells

We investigated the effect of ionic liquid molecules (ILMs) in hybrid quantum dot-organic solar cells (HyQD-OSCs). The insertion of an ILM layer between PbS and phenyl-C61-butyric acid methyl ester (PCBM) can shift the band edge of PCBM closer to the vacuum level of PbS due to spontaneous dipole polarization. Because of this new architecture, improvements in device performance were achieved, including increases in open-circuit voltage (VOC, from 0.41 V to 0.49 V), fill factor (FF, from 0.48 to 0.59), and power conversion efficiency (PCE, from 1.62% to 2.21%), compared to reference devices under AM 1.5G illumination at 100 mW cm(-2). We observed that treatment of the PbS layer with ILMs causes a significant increase in work function from 3.58 eV to 3.93 eV. Furthermore, the ILMs layer minimizes the contact resistance between PbS and PCBM due to the improved compatibility between the two layers, confirmed as a decrease in charge transfer resistance, as measured by electrical impedance spectroscopy.

Vapor coating method using small-molecule organic surface modifiers to replace N-type metal oxide layers in inverted polymer solar cells.

We investigate a simple fabrication method for vapor coating small-molecule organic interlayers as replacements for metal oxide films. The interfacial layers, which serve both as both surface modifiers to reduce the substrate work function and electron selective layers, maximize light absorption within the active layer while improving electron transport and compatibility between the active layer and cathode, leading to a ∼22% enhancement in power conversion efficiency and similar air stability compared to devices using a ZnO layer.

Peroptronic devices: perovskite-based light-emitting solar cells

Solution processed perovskite semiconductors have developed rapidly over the past decade to yield excellent performance in both solar cell and light emitting diode devices. Both of these device types are prepared using similar materials and architectures, raising the possibility of perovskite based light emitting solar cells. Recent reports have indicated that some low band gap perovskite solar cells are able to emit infrared light efficiently, however, intermediate band gap perovskite solar cells which emit visible light have not, to the best of our knowledge been deliberately designed or extensively characterized. In this work, we have investigated the use of different electron transport layers in order to minimize energetic barriers to electron injection and extraction in methylammonium lead bromide (MAPbBr3) films. We demonstrate that through appropriate band structure engineering, MAPbBr3 can be used to make such “peroptronic” light-emitting solar cells, which simultaneously exhibit efficient solar cell power conversion efficiencies over 1% and 0.43 lm W−1 green light emission.

The introduction of a perovskite seed layer for high performance perovskite solar cells

Processing for obtaining compact and uniform perovskite photoactive layers has been intensively studied over the last few years to achieve high power conversion efficiencies (PCEs) in solar cells. Particularly, high quality crystal growth of perovskite layers is critical to enhance device performance. We demonstrate an easy and effective new process for high efficiency p–i–n planar heterojunction structures of perovskite solar cells (PeSCs) by using a compact seed perovskite layer (CSPL). The CSPL assists vertical growth of perovskite crystals and obtains the highly crystalline perovskite photoactive layer, which leads to the reduction in the charge transfer resistance and a longer photoluminescence lifetime. The PeSC device with a CSPL shows a remarkably improved PCE, from 15.07% to 19.25%, with a record open circuit voltage (VOC) of 1.16 V in the p–i–n structure with pure crystal perovskite and negligible current density–voltage hysteresis. Additionally, a PCE of 20.37% was achieved in CSPL assisted n–i–p structure PeSCs.