Solar Module Application and Characterization Lab | Focuses
- Thermoelectric materials synthesis and characterization
- Low grade heat harvesting and cooling
- High temperature power generation
- Device fabrication and testing
1. Flexible Solar Cell Module
Flexible solar modules offer many advantages including (a) lightweight materials and structures, (b) the ability to conform to irregular and complex surfaces, and (c) simpler integration with wearable and portable systems. However, the transition from lab size solar cells to module type solar cells is challenging because of the difficulties of uniform large film synthesis, structure design, component integration, and so forth. Our research is focused upon addressing all aspects of the flexible solar modules including material and/or device fabrication, basic mechanisms, component or/and module design, structure-property relationships, theoretical and/or numerical modeling, physics of devices, new system architectures, scaling challenges, system integration, and practical demonstrations.
2. Self-Assembly of Perovskite Thin Film
Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted tremendous attention in past few years, owing to the unprecedented enhancement in light-electricity conversion efficiency. The fabrication of high quality perovskite photoactive layer dominantly determines the performance and deployment of PSCs. We developed a facile, green and cost-effective synthesis method, realizing the transition from perovskite crystals to thin films. The CH3NH3PbI3 single crystal was exfoliated by methylamine CH3NH2 and then transformed into liquid 2D layered perovskite intermediate (LPI). The exposed cations in the basal plane provide active sites for the complexation between LPI and PMMA, and the sequential self-assembly (SA) of the complexed LPI results in the perovskite grains coated with a monolayer of PMMA protective layer, providing a homogeneous hybrid microstructure to increase the stability against environmental factors.
3. Quasi-Two-Dimensional Halide Perovskite Single Crystal Photodetector
The robust material stability of the quasi-two-dimensional (quasi-2D) metal halide perovskites has opened the possibility for their usage instead of three-dimensional (3D) perovskites. Further, devices based on large area single crystal membranes have shown increasing promise for photoelectronic applications. However, growing inch-scale quasi-2D perovskite single crystal membranes (quasi-2D PSCMs) has been fundamentally challenging. Here we report a fast synthetic method for synthesizing inch-scale quasi-2D PSCMs, namely (C4H9NH3)2(CH3NH3)n−1PbnI3n+1 (index n = 1, 2, 3, 4, and ∞), and demonstrate their application in a single-crystal photodetector. A quasi-2D PSCM has been grown at the water–air interface where spontaneous alignment of alkylammonium cations and high chemical potentials enable uniform orientation and fast in-plane growth. Structural, optical, and electrical characterizations have been conducted as a function of quantum well thickness, which is determined by the index n. It is shown that the photodetector based on the quasi-2D PSCM with the smallest quantum well thickness (n = 1) exhibits a strikingly low dark current of ∼10–13 A, higher on/off ratio of ∼104, and faster response time in comparison to those of photodetectors based on quasi-2D PSCMs with larger quantum well thickness (n > 1). Our study paves the way toward the merging the gap between single crystal devices and the emerging quasi-2D perovskite materials.
4. Mono-crystalline Perovskite Photovoltaics toward Ultrahigh Efficiency?
PVs with higher efficiency would reduce the payback time and compensate for the high facility expenses and capital costs. Mono-perovskite PVs represent a promising avenue for ultrahigh efficiency. Overcoming the remaining technical challenges within mono-crystalline film/wafer growth and device design will provide opportunities to approach and even break the Shockley-Queisser limit. Preliminary demonstrations of mono-crystalline growth techniques as well as simple device prototypes are good indications suggesting that advances in this area are going to meet the expectations. In this work, we discussed the prospective and challenges for realizing Mono-crystalline Perovskite Photovoltaics in order to get ultra-high power-conversion-efficiency in the future.
5. High Efficient Two-Dimensional Perovskite Solar Cells
Recently, Ruddlesden-Popper 2D perovskite materials have been shown to exhibit superior stability owing to their beneficial geometric effect and dielectric contrast effect; unfortunately, the efficiency of 2D PSCs is much lower because of severe charge recombination affected by large exciton binding energy, poor carrier transport caused by quantum wells, and low conductivity produced by insulating long chain organic spacer cations. At that point, we developed a short chain methylammonium (MA)-based two-dimensional perovskite thin film using vapor-fumigation technology. Compared to the traditional 2D perovskite based on long chain butylammonium (BA) cations, its exciton binding energy significantly decreases to 172 meV from 510 meV due to the high dielectric constant of MA. And the tunneling probability of a carrier through a quantum well increases by four orders of magnitude because of the smaller layer spacing, which decreases to 9.08 A from 13.39 A. In addition, theoretical calculations and experimental analysis reveal that the MA-based 2D perovskites possess a narrow band gap, good conductivity, and a low trap density. As a result, the efficiency of the 2D PSCs is up to 16.92%, and the certified efficiency is 16.6% according to the National Institute of Metrology (NIM), the highest efficiency so far for 2D PSCs. Furthermore, the MA-based 2D PSCs exhibit superior long-term stability under illumination and exposure to environmental conditions. When the unsealed 2D perovskite devices store in ambient air exceeded 1500 hours, or even under continuously illuminated for 500 hours, the efficiency maintains about 96% of its initial value. The high efficiency and superior stability demonstrate that the present method provides a promising pathway towards high quality 2D perovskites for potential commercial applications.
6. Bio-solar cells development
Biomaterials such as DNA has shown attractive structural and physical properties but there are numerous mysteries remained. Our research aims to construct hybrid optoelectronic devices coupling naturally derived biomaterials with other semiconductor materials such as inorganic-organic perovskites. By studying the device performance, it is expected properties and underlying mechanism of biomaterial can be revealed. In addition, integrating biomaterial into devices may also bring new possibilities for next-generation optoelectronics.
The power conversion efficiencies of perovskite solar cells (PSCs) have reached 23.3% recently, rivaling those of established photovoltaic technologies. For PSCs to be commercially competitive, one of the important challenges is to overcome the limitations of small area and excessive material waste from spin-coating. Electrospray printing is a scalable and roll-to-roll compatible method with high material utilization rate. We reported an all electrospray printing process for PSCs in ambient air below 150 °C which leads to pin-hole free, smooth and uniform perovskite layer, hole transport layer and electron transport layer. The power conversion efficiency of the all electrospray printed devices reaches up to 15.0%, which is the highest to date for fully printed PSCs using mainstream printing methods in air without significant material waste.