Organic Solar Cells—The Path to Commercial Success

Abstract

This, combined with little material consumption (≈1 g organic semiconductor per m 2 ), low-temperature processing and the compatibility with flexible substrates enables light-weight devices made in roll-toroll production and a large versatility in applications. This could make OSC the cheapest source of electricity in the world.The main difference in operation between silicon solar cells and OSC, and the reason that OSCs lag silicon solar in their commercialization, is that light absorption in organic semiconductor thin films does not lead to efficient generation of free charge carriers, but to the generation of strongly bound excitons having limited diffusion length. A solution to the former was published by Tang in 1986: [6,7] efficient exciton separation was achieved at the planar interface between two different organic semiconductors, an electron donor and an electron acceptor, leading to a type II heterojunction. The key concept for overcoming the limited exciton diffusion length was introduced by Hiramoto et al. [8] in 1991 by co-evaporating donor and acceptor molecules, leading to a bulk heterojunction (BHJ) with a distributed donor-acceptor interface. Here, each exciton is generated within its diffusion length of the heterojunction. Such BHJs are at the core of all efficient OSC today, independent whether they are processed in vacuum or made via solution-based processes. A typical OSC stack structure, along with a monolithic series connection of subcells into a module, is shown in Figure 1.Continuous research and development of organic semiconductors tailored for OSC, of processing techniques and stack design, have led to materials with better absorption and donor-acceptor energy offsets, [9,10] optimization of the BHJ microstructure, [11,12] and stack design, [13,14] pushing power conversion efficiencies (PCEs) to around 18% in single-junction solar cells. [15] PCEs of >20% appear to be within reach and module efficiencies are catching up with these values.PCEs of OSC devices and modules are important, but due to the further balance of system cost in a photovoltaic system [16] a high PCE alone is not sufficient for OSC to contribute at scale to solving climate change. For this, sufficient lifetime and scalability to terawatts of installed capacity at competitive cost are required, as well. In the following, we highlight some of the key research challenges, discuss OSC markets, and give an outlook on the transformative potential of OSC in terms of cost and carbon emissions. Research Challenges Voltage LossesOSCs can achieve short circuit current densities [22] and fill factors [23] on par with the ones of GaAs or perovskite-based devices Organic solar cells have the potential to become the cheapest form of electricity, beating even silicon photovoltaics. This article summarizes the state of the art in the field, highlighting research challenges, mainly the need for an efficiency increase as well as an improvement in long-term stability. It discusses possible current and future applications, such as buildi...

A Review on Printed Electronics: Fabrication Methods, Inks, Substrates, Applications and Environmental Impacts

“…With a global market share of about 90%, the silicon solar cells have power conversion efficiencies (PCEs) varying between 19 and 25% [99][100][101]. Printable solar cells, on the other hand, are promising candidates to harvest energy for niche applications such as wearable textile electronics to charge low-power devices and building-integrated systems to harvest energy from solar cells placed on roofs, windows or facades of buildings [102]. In these applications, the fabrication scalability, light-weight, flexibility and transparency are vital.…”

Tuning Aggregation Behavior of Polymer Donor viaMolecular‐Weight Control for Achieving 17.1% Efficiency Inverted Polymer Solar Cells

“…[ 1‐5 ] Nowadays, the power conversion efficiencies (PCEs) for single junction PSCs have exceeded the threshold for commercial viability of 15%. [ 6‐9 ] Remarkable breakthroughs should be attributed to many factors, including materials development, morphology control, device physics, device structure optimization, and so on. [ 10‐14 ] Specially, the development of non‐fullerene acceptors (NFAs) has further promoted state‐of‐the‐art PSCs to reach the milestone PCE of over 18%.…”

Reducing Non‐Radiative Voltage Losses by Methylation of Push–Pull Molecular Donors in Organic Solar Cells

“…Compound 1 b was effectively prepared by a Buchwald-Hartwig amination between N,4-dimethylaniline and 1-bromo-4-iodobenzene using [1,1'-biphenyl]-2-yldicyclohexylphosphane as ligand. Compounds were then engaged in a Pdcatalyzed cross-coupling reaction with 7-bromobenzo[c] [1,2,5] thiadiazole-4-carbaldehyde [34] affording aldehydes 3 a and 3 b. A subsequent Knoevenagel condensation with malononitrile led to MPA and Me-MPA (Scheme 1).…”

“…[18,19] In this context, small push-pull D-π-A molecules where an electron-donating block is connected to an electron-accepting group through a πconjugated spacer have been widely investigated as promising donor materials in OPV. [20][21][22][23][24][25] For example, high-efficiency vacuum-processed OSCs using 2-[(7-(4-[N,N-bis(4-methylphenyl)amino]phenyl)-2,1,3-benzothia-diazol-4-yl)methylene]propane-dinitrile (DCDCPB) and its thiophenic analogue 2-((7-(5-(dip-tolylamino)thiophen-2-yl)benzo[c] [1,2,5]thiadiazol-4-yl)methylene (DTDCTB) donors were reported, showing exceptionally long exciton diffusion lengths (see the Supporting Information, Figure S1). [26][27][28] In these push-pull molecules, a benzothiadiazole (BTZ) π-spacer connects the dicyanovinyl (DCV) electron-acceptor block to two different arylamine-based donor blocks exhibiting two methyl groups at the parapositions of the two external phenyl rings.…”