In recent years, the power conversion efficiency of perovskite solar cells has increased to reach over 20%. Finding an effective means of defect passivation is thought to be a promising route for bringing further increases in the power conversion efficiency and the open-circuit voltage (VOC) of perovskite solar cells. Here, we report the use of an organic halide salt phenethylammonium iodide (PEAI) on HC(NH2)2–CH3NH3 mixed perovskite films for surface defect passivation. We find that PEAI can form on the perovskite surface and results in higher-efficiency cells by reducing the defects and suppressing non-radiative recombination. As a result, planar perovskite solar cells with a certificated efficiency of 23.32% (quasi-steady state) are obtained. In addition, a VOC as high as 1.18 V is achieved at the absorption threshold of 1.53 eV, which is 94.4% of the Shockley–Queisser limit VOC (1.25 V). Planar perovskite solar cells that have been passivated using the organic halide salt phenethylammonium iodide are shown to have suppressed non-radiative recombination and operate with a certified power conversion efficiency of 23.3%.

Surface passivation of perovskite film for efficient solar cells

Although organic photovoltaic (OPV) cells have many advantages, their performance still lags far behind that of other photovoltaic platforms. A fundamental reason for their low performance is the low charge mobility of organic materials, leading to a limit on the active-layer thickness and efficient light absorption. In this work, guided by a semi-empirical model analysis and using the tandem cell strategy to overcome such issues, and taking advantage of the high diversity and easily tunable band structure of organic materials, a record and certified 17.29% power conversion efficiency for a two-terminal monolithic solution-processed tandem OPV is achieved.

https://science.sciencemag.org/content/sci/early/2018/08/08/science.aat2612.full.pdf

Organic and solution-processed tandem solar cells with 17.3% efficiency

The efficiencies of perovskite solar cells have gone from single digits to a certified 22.1% in a few years' time. At this stage of their development, the key issues concern how to achieve further improvements in efficiency and long-term stability. We review recent developments in the quest to improve the current state of the art. Because photocurrents are near the theoretical maximum, our focus is on efforts to increase open-circuit voltage by means of improving charge-selective contacts and charge carrier lifetimes in perovskites via processes such as ion tailoring. The challenges associated with long-term perovskite solar cell device stability include the role of testing protocols, ionic movement affecting performance metrics over extended periods of time, and determination of the best ways to counteract degradation mechanisms.

http://science.sciencemag.org/content/sci/358/6364/739.full.pdf

Promises and challenges of perovskite solar cells

With rapid progress in a power conversion efficiency (PCE) to reach 25%, metal halide perovskite-based solar cells became a game-changer in a photovoltaic performance race. Triggered by the development of the solid-state perovskite solar cell in 2012, intense follow-up research works on structure design, materials chemistry, process engineering, and device physics have contributed to the revolutionary evolution of the solid-state perovskite solar cell to be a strong candidate for a next-generation solar energy harvester. The high efficiency in combination with the low cost of materials and processes are the selling points of this cell over commercial silicon or other organic and inorganic solar cells. The characteristic features of perovskite materials may enable further advancement of the PCE beyond those afforded by the silicon solar cells, toward the Shockley-Queisser limit. This review summarizes the fundamentals behind the optoelectronic properties of perovskite materials, as well as the important approaches to fabricating high-efficiency perovskite solar cells. Furthermore, possible next-generation strategies for enhancing the PCE over the Shockley-Queisser limit are discussed.

High-Efficiency Perovskite Solar Cells.

A semiconductor that can be processed on a large scale with a bandgap around 1.8 eV could enable the manufacture of highly efficient low cost double-junction solar cells on crystalline Si. Solution-processable organic–inorganic halide perovskites have recently generated considerable excitement as absorbers in single-junction solar cells, and though it is possible to tune the bandgap of (CH3NH3)Pb(BrxI1–x)3 between 2.3 and 1.6 eV by controlling the halide concentration, optical instability due to photoinduced phase segregation limits the voltage that can be extracted from compositions with appropriate bandgaps for tandem applications. Moreover, these materials have been shown to suffer from thermal degradation at temperatures within the processing and operational window. By replacing the volatile methylammonium cation with cesium, it is possible to synthesize a mixed halide absorber material with improved optical and thermal stability, a stabilized photoconversion efficiency of 6.5%, and a bandgap of 1.9 eV.

Cesium Lead Halide Perovskites with Improved Stability for Tandem Solar Cells

The efficiency of silicon solar cells has a large influence on the cost of most photovoltaics panels. Here, researchers from Kaneka present a silicon heterojunction with interdigitated back contacts reaching an efficiency of 26.3% and provide a detailed loss analysis to guide further developments.

Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26

We have applied an optical splitting system in order to achieve very high conversion efficiency for a full spectrum multi-junction solar cell. This system consists of multiple solar cells with different band gap optically coupled via an “optical splitter.” An optical splitter is a multi-layered beam splitter with very high reflection in the shorter-wave-length range and very high transmission in the longer-wave-length range. By splitting the incident solar spectrum and distributing it to each solar cell, the solar energy can be managed more efficiently. We have fabricated optical splitters and used them with a wide-gap amorphous silicon (a-Si) solar cell or a CH3NH3PbI3 perovskite solar cell as top cells, combined with mono-crystalline silicon heterojunction (HJ) solar cells as bottom cells. We have achieved with a 550 nm cutoff splitter an active area conversion efficiency of over 25% using a-Si and HJ solar cells and 28% using perovskite and HJ solar cells.

High efficiency solar cells combining a perovskite and a silicon heterojunction solar cells via an optical splitting system

A solar cell includes: first conductivity-type layers and second conductivity-type layers each provided on a rear surface of a semiconductor substrate; first electrodes provided on the first conductivity-type layers; and second electrodes provided on the second conductivity-type layers The first electrodes and the second electrodes are spaced apart from each other, and the first electrodes include a plurality of regions isolated from one another by the second electrodes disposed therebetween Each of the plurality of regions of the first electrodes includes a non-mounting electrode section and a wiring-mounting electrode section having a larger electrode height than the non-connection electrode section In two adjacent first electrode regions, an imaginary line connecting the top of the wiring-mounting electrode section of one of the regions and the top of the wiring-mounting electrode section of the other region does not cross the second electrode disposed between the two regions

Solar battery and solar battery module

PROBLEM TO BE SOLVED: To provide a silicon solar battery that can reduce leak current and increase a conversion efficiency, and a manufacturing method for the same.SOLUTION: A method of manufacturing a crystal silicon solar battery that has a conduction type single crystal silicon substrate 1, an inverse conduction type silicon-based layer 3a and a first transparent electrode layer 4a which are provided on a first primary face of the substrate in this order, and a second primary face side electrode layer 8 at a second primary face side, comprises: a first transparent electrode layer forming step for forming a first transparent electrode layer on the first primary face of the inverse conduction type silicon-based layer, and a cleaving step of cleaving a crystal silicon solar battery product having a first transparent electrode layer in progress into plural parts in this order. The method further comprises an opening area forming step of forming a first transparent electrode layer opening area having no first transparent electrode layer on the first primary face side surface of the substrate before the cleaving step. The cleaving step preferably contains a laser irradiating step of irradiating the first transparent electrode layer opening area with a laser beam so that at least a part of the substrate is exposed from the first primary face side.

Crystal silicon solar battery, manufacturing method for the same and solar battery module

Provided is a solar cell module having a crystalline silicon solar cell (4) and an interconnector (3) that is electrically connected to the crystalline silicon solar cell. The interconnector has a width of greater than or equal to 50 µm and less than 400 µm, and is disposed so as to electrically connect a plurality of finger electrodes while crossing the same. The crystalline silicon solar cell has a plurality of finger electrodes (9) that are provided in parallel arrangement on a photoelectric conversion unit (50), and is provided with an insulating layer (8) so as to cover a primary surface of the photoelectric conversion unit and the finger electrodes. In portions where the finger electrodes intersect with the interconnector, the finger electrodes and the interconnector are electrically connected through an opening provided in the insulating layer between each finger electrode and the interconnector.

Kunihiro Nakano

Papers

Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26

High efficiency solar cells combining a perovskite and a silicon heterojunction solar cells via an optical splitting system

Solar battery and solar battery module

Crystal silicon solar battery, manufacturing method for the same and solar battery module

Crystalline silicon solar cell module and manufacturing method for same