Ye-Jin Jeon

Planar heterojunction perovskite solar cells with superior reproducibility

Perovskite solar cells (PeSCs) have been considered one of the competitive next generation power sources. To date, light-to-electric conversion efficiencies have rapidly increased to over 10%, and further improvements are expected. However, the poor device reproducibility of PeSCs ascribed to their inhomogeneously covered film morphology has hindered their practical application. Here, we demonstrate high-performance PeSCs with superior reproducibility by introducing small amounts of N-cyclohexyl-2-pyrrolidone (CHP) as a morphology controller into N,N-dimethylformamide (DMF). As a result, highly homogeneous film morphology, similar to that achieved by vacuum-deposition methods, as well as a high PCE of 10% and an extremely small performance deviation within 0.14% were achieved. This study represents a method for realizing efficient and reproducible planar heterojunction (PHJ) PeSCs through morphology control, taking a major step forward in the low-cost and rapid production of PeSCs by solving one of the biggest problems of PHJ perovskite photovoltaic technology through a facile method.

Metal chloride-treated graphene oxide to produce high-performance polymer solar cells

We introduce a simple but effective graphene oxide (GO) modification with metal chloride treatments to produce high-performance polymer solar cells (PSCs). The role of various metal chlorides on GO and their effects on device performances of PSCs was investigated. X-ray photoelectron spectroscopy, ultraviolet photoemission spectroscopy, and current-voltage measurement studies demonstrated that metal chloride can induce a p-doping effect and increase the GO work-function, thus resulting in an improved built-in potential and interfacial resistance in PSCs. The resultant PSCs with metal chloride exhibited improved device efficiency than those with the neat GO. Furthermore, with the metal chloride-doped GO, we finally achieved an excellent PSC-efficiency of 6.58% and a very desirable device stability, which constitute a highly similar efficiency but much better PSC life-time to conventional device with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). This study could be a valuable way to produce various PEDOT:PSS alternatives and beneficial for producing high-performance and cost-efficient polymeric devices.

Slot-Die Coated Perovskite Films Using Mixed Lead Precursors for Highly Reproducible and Large-Area Solar Cells

Recently, many kinds of printing processes have been studied to fabricate perovskite solar cells (PeSCs) for mass production. Among them, slot-die coating is a promising candidate for roll-to-roll processing because of high-throughput, easy module patterning, and a premetered coating system. In this work, we employed mixed lead precursors consisting of PbAc2 and PbCl2 to fabricate PeSCs via slot-die coating. We observed that slot-die-coated perovskite films based on the mixed lead precursors exhibited well-grown and uniform morphology, which was hard to achieve by using only a single lead source. Consequently, PeSCs made with this precursor system showed improved device performance and reproducibility over single PbAc2. Lastly, a large-area module with an active area of 10 cm2 was fabricated with a power conversion efficiency of 8.3%.

Structure–property relationship of D–A type copolymers based on phenanthrene and naphthalene units for organic electronics

Four donor–acceptor (D–A) type conjugated polymers (PA1, PA2, PA3 and PA4) based on phenanthrene and naphthalene as the donating units with or without dimethoxy substitution were synthesized for organic field effect transistors (OFETs) and bulk-heterojunction organic photovoltaics (OPVs). Dimethoxy substituents have significant effects on the optical, electrochemical, charge transport and photovoltaic properties depending on the donor-polyaromatic (PA) compounds. The optical band gaps of these PA-based copolymers from the smallest to the largest are as follows: 1.52 eV (1,5-dimethoxy substituted naphthalene (PA4)), 1.59 eV (unsubstituted naphthalene (PA3)), and 1.63 eV (unsubstituted phenanthrene (PA1), and substituted 9,10-dimethoxy phenanthrene (PA2)). While the values vary depending on the compounds, both PA2 and PA4 are found to have higher highest occupied molecular orbital (HOMO) energy levels than those of PA1 and PA3 due to the electron donating nature of dimethoxy substituents. The PA based copolymers without dimethoxy substituents showed highly balanced ambipolar behavior with ∼1 cm2 V−1 s−1, whereas the electron mobility of dimethoxy modified PA (MeOPA) based copolymers was suppressed. The inverted bulk heterojunction OPVs based on PA1 and PA3 exhibited power conversion efficiency (PCE) as high as 5.3% and 5.8%, respectively. The PCEs of PA copolymer-based OPV devices were mainly affected by an increase in the open circuit voltage rather than by the photocurrent or fill factor.

Small-Molecule Organic Photovoltaic Modules Fabricated via Halogen-Free Solvent System with Roll-to-Roll Compatible Scalable Printing Method

For the first time, the photovoltaic modules composed of small molecule were successfully fabricated by using roll-to-roll compatible printing techniques. In this study, blend films of small molecules, BTR and PC71BM were slot-die coated using a halogen-free solvent system. As a result, high efficiencies of 7.46% and 6.56% were achieved from time-consuming solvent vapor annealing (SVA) treatment and roll-to-roll compatible solvent additive approaches, respectively. After successful verification of our roll-to-roll compatible method on small-area devices, we further fabricated large-area photovoltaic modules with a total active area of 10 cm2, achieving a power conversion efficiency (PCE) of 4.83%. This demonstration of large-area photovoltaic modules through roll-to-roll compatible printing methods, even based on a halogen-free solvent, suggests the great potential for the industrial-scale production of organic solar cells (OSCs).