24 - 28 October 2016 • Marina Bay Sands Sands Expo and Convention Centre, Singapore
Organo-metal-halide Perovskite Solar Cells – Past, Present, and Future
Organo metal halide perovskites, represented by CH3NH3PbX3 (X=Br, I), are ionic crystals exhibiting multi-functions in photovoltaic power generation and optoelectronics with high extinction coefficient, 105 cm-1, for visible light. In 2008 we fabricated the first perovskite solid-state photovoltaic cell with a carbon-polymer composite hole transport material. Rapid progress in preparation of high quality perovskite crystals enabled power conversion efficiency (PCE) to reach 22%. Our group has focused on low temperature-based high throughput process and design of perovskite cells with stable hysteresis-less performance. We made plastic film-based flexible perovskite cells by using SnO2 and brookite TiO2 as electron collectors, which work with non-hysteretic PCE>13% with high mechanical stability against bending. Formamidinium-based perovskites are promising materials with good heat resistance and are capable of PCE of 20% and more. However, lead-free new materials are sought after as next direction of printable hybrid perovskite materials. My talk will present metal oxide-based lead halide perovskite cells with high stability and performance and lead-free type perovskite cells as a new direction.
The electrical properties of CIGS film are critically affected by the bulk point defects in addition to interfacial defects. Especially the donor-type point defects such as Se vacancy and antisite defect should be well suppressed. We found that those defects can be reduced by simple Se annealing at 300°C. As a result, the short-circuit current of the CIGS solar cell clearly increased, while the fill factor and open-circuit voltage were degraded. With an appropriate surface treatment of the CIGS film in addition to Se annealing, the fill factor and open-circuit voltage of CIGS cells also increased significantly in addition to the short-circuit current. We will report examples of defect control in α-CIGS and β-CIGS films. The origin of the cell performance enhancement was described by analyzing the low temperature photoluminescence, x-ray photoelectron spectroscopy, the reverse saturation current from diode curves, and the carrier lifetimes from time-resolved photoluminescence.
Abstract to be uploaded soon.
Perovskite is a promising light harvester for use in photovoltaic solar cells. In recent years, the power conversion efficiency of perovskite solar cells has been dramatically increased, making them a competitive source of renewable energy. This work will discusses new directions related to organic inorganic perovskite and their applications in solar cells.
In low dimensional systems, stability of excitons in quantum wells is greatly enhanced due to the confined effect and the coulomb interaction. The exciton binding energy of the typical 2D organic-inorganic perovskites is up to 300 meV and their self-assembled films exhibit bright photoluminescence at room temperature.
We have already reported the interface architecture of perovskite (PVK: MAPbI3)/titania and proved that passivating the interface and decreasing the trap density at the interface is very important for enhancing solar cell efficiency. In this report, the architecture of other interface, namely, interface at PVK and hole transport layer will be discussed. The device has FTO-glass / compact titania / porous titania / PVK / SPIRO (hole ransport layer) / Au structure. After the interface between PVK and SPIRO was passivated, the photovoltaic efficiency increased from 14.5% to 17.6%. Interestingly, PVK grain boundary was also passivated. The charge recombination time scale between the PVK and SPIRO became longer from 0.3μsec to 60 μsec, drastically, leading to the conclusion that the PVK/SPIRO interface has large trap densities (charge recombination centers). The relationship between the passivation structure and solar cell performances will be discussed in detail.
Solar Frontier K.K. has been working on the research of several chalcogenide solar cells, Cu(In,Ga)(Se,S)2 (CIGSeS), Se-free Cu(In,Ga)S2 (CIGS), Cu2ZnSn(Se,S)4 and Se-free Cu2ZnSnS4. Recently, 22.3% conversion efficiency (Eff) on CIGSeS and 15.5% Eff on Se-free CIGS thin-film solar cells were achieved (both were confirmed by Fraunhofer ISE) as shown in Fig. 1 [1,2].
In this paper, we will especially focus on the Se-free CIGS solar cell and discuss about a new challenge for the Eff improvement. We have boosted the Eff of Se-free CIGS owing to open-circuit voltage and current density improvements by Ga-profile control and Cd-free buffer application. However, the fill-factor was still low, and it is assumed that the rough absorber made shunt passes.
Thus, we tried to obtain the flat absorber to prevent the shunt passes. Finally, the flat absorber was obtained by a new method as shown in Fig. 2. The detail of the electrical parameters will be presented at the conference.
Stability of Perovskite Solar Cells against Light and HeatOrganic-inorganic hybrid perovskite (CH3NH3PbI3) solar cells have been studied intensively for new energy resource of our future society, due to the high conversion efficiency. However, the CH3NH3PbI3 perovskite is quite unstable material. In this presentation, the efforts to improve and understand the stability issue of perovskite solar cells will be summarized. Specially, results of thermal stabile perovskite solar cells at 100 ºC will be presented.
Sequential processing of Cu(In,Ga)(S,Se)2 (CIGS) absorber layers is a viable industrial process for CIGS solar module fabrication. Large-scale state of the art technology still relies on the use of toxic gases such as H2Se/H2S for chalcogenization, driving up production costs. Here we present a sequential process routine, which employs fast atmospheric in-line chalcogenization of sputtered Cu-In-Ga precursors on Mo-coated glass using elemental Se and S as chalcogen sources. Ga aggregation at the back contact - as generally seen in sequentially processed CIGS thin films – and sulfurization of a partially selenized precursor seems to give good control over the in-depth Eg grading of the complete absorber. We find that type and amount of Na supply have considerable impact on the S in-depth profile. In addition sulfur implementation can result in evolution of different device defects such as e.g. the development of a barrier at the front (CIGSSe/CdS) or back interface
Perovskite solar cells have demonstrated a great potential for the high efficiency but still have to prove the long-term stability. Perovskite cells exhibit degradation upon exposure to moisture, UV light, heat, and electric field. We herein examined the degradation of perovskite solar cells in the presence of UV light alone, excluding the effects of moisture, oxygen, and other part of the solar light spectrum. Perovskite solar cells were exposed to 365 nm UV light for over 1,000 h in argon at <0.5 ppm humidity without encapsulation. The stability of perovskite cells was also observed under various electric bias conditions up to 1.2V. Some of the degraded cells showed a recovery under certain conditions. In this paper, the precise conditions will be presented that cause the degradation and the recovery, and the mechanisms behind the phenomena will also be presented.
The CIGS cell efficiency is now approaching 23%, thanks to the recent advancement in the front surface passivation scheme for the CIGS absorber layer. In this paper, we describe a number of key R&D items for further efficiency enhancement and for commercial implementation by considering in detail the performance losses in the small-area unit cell all the way to the large-area commercial-size module. Key process parameters for the efficiency enhancement were determined and a roadmap to 19% module efficiency without a major change in the manufacturing process was developed. The manufacturing cost broken down to each unit process was analyzed to identify the steps critical for cost reduction and to determine the tradeoff between the efficiency enhancement and the corresponding additional cost. Taking into account the economy of scale and the enhancement in the module efficiency, the road to manufacturing cost below $0.30/Wp is presented.