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

With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic–inorganic perovskite materials.

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High-efficiency crystalline silicon solar cells: status and perspectives

Photovoltaic solar cells based on metal halide perovskites have gained considerable attention over the past decade because of their potentially low production cost, earth-abundant raw materials, ease of fabrication and ever-increasing power conversion efficiencies of up to 25.2%. This type of solar cells offers the promise of generating electricity at a more competitive unit price than traditional fossil fuels by 2035. Nevertheless, the best research cell efficiencies are still below the theoretical limit defined by the Shockley-Queissier theory owing to the presence of non-radiative recombination losses. In this Review, we analyse the predominant pathways that contribute to non-radiative recombination losses in perovskite solar cells, and evaluate their impact on device performance. We then discuss how non-radiative recombination losses can be estimated through reliable characterization techniques, and highlight some notable advances in mitigating these losses, which hint at pathways towards defect-free perovskite solar cells. Finally, we outline directions for future work that will push the efficiency of perovskite solar cells towards the radiative limit.

Minimizing non-radiative recombination losses in perovskite solar cells

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pip.2728

Solar cell efficiency tables (version 47)

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pip.2788

Solar cell efficiency tables (version 48)

The crystalline silicon heterojunction structure adopted in photovoltaic modules commercialized as Panasonic's HIT has significantly reduced recombination loss, resulting in greater conversion efficiency. The structure of an interdigitated back contact was adopted with our crystalline silicon heterojunction solar cells to reduce optical loss from a front grid electrode, a transparent conducting oxide (TCO) layer, and a-Si:H layers as an approach for exceeding the conversion efficiency of 25%. As a result of the improved short-circuit current (J
 sc
), we achieved the world's highest efficiency of 25.6% for crystalline silicon-based solar cells under 1-sun illumination (designated area: 143.7 cm
 2
).

Achievement of More Than 25% Conversion Efficiency With Crystalline Silicon Heterojunction Solar Cell

PROBLEM TO BE SOLVED: To provide a concave-convex substrate fabrication method for reducing an amount of etching liquid variation between lots and constantly forming a uniform projection-recess structure on the surface and a method for fabricating a photovoltaic element using the concave-convex substrate SOLUTION: This method submerges a crystal silicon substrate in an alkaline solution and provides anisotropic etching on a surface of the substrate to form a projection-recess structure on the surface for concave-convex substrate fabrication The alkaline solution contains an addition agent represented in the chemical formula (1):Where, X represents a carboxyl group, sulfonic group, sulfate ester group, phosphoester group or quaternary ammonium while R1 to R5 represent a hydrogen atom, alkyl group, alkenyl group and alkoxy group COPYRIGHT: (C)2008,JPO&INPIT

Concave-convex substrate fabrication method and photovoltaic element fabrication method

A method for making an irregularly surfaced substrate by immersing a crystalline silicon substrate in an alkaline solution to anisotropically etch a surface of the substrate so that an irregularity structure is imparted to the surface of the substrate. The alkaline solution contains an additive represented by the following general formula (1):
 
(in the formula, X is a carboxyl, sulfonic, sulfate ester, phosphate ester or quaternary ammonium group; R1 - R5 are independently a hydrogen atom or an alkyl, alkenyl or alkoxy group; and at least one of R1 - R5 has 3 or more carbon atoms) .

Method for making irregularly surfaced substrate and method for fabricating photovoltaic device

A method for making a concavo-convex substrate and a method for making a photovoltaic element are provided to form stably a constant concavo-convex structure on a silicon substrate by using an alkali solution including an additive. A crystal silicon substrate(1) is dipped into an alkali solution. A surface of the crystal silicon substrate is etched by using an anisotropic etch method to form a concavo-convex structure on a surface(1a) of the substrate. The alkali solution includes an additive having a chemical structure. The chemical structure includes X and R1-R5 where X is one of carboxyl, sulfonic, sulfate ester, phosphate ester, quaternary ammonium groups, R1-R5 are one of hydrogen atom, alkyl, alkenyl, and alkoxy groups, and at least one of R1-R5 has 3 or more carbon atoms.

Naoki Yoshimura

Papers

Achievement of More Than 25% Conversion Efficiency With Crystalline Silicon Heterojunction Solar Cell

Concave-convex substrate fabrication method and photovoltaic element fabrication method

Method for making irregularly surfaced substrate and method for fabricating photovoltaic device

Method for making a concave and convex substrate and method for making a photovoltaic element