Toward High‐Performance Semi‐Transparent Polymer Solar Cells: Optimization of Ultra‐Thin Light Absorbing Layer and Transparent Cathode Architecture

Abstract

Organic photovoltaics (OPVs) have recently attracted extensive interest due to their potential for low cost, high throughput manufacturing to solve the scalability problem in solar energy. A typical OPV is based on the bulk-heterojunction (BHJ) device confi guration, which sandwiches a layer of polymer donor and fullerene acceptor blend between a transparent electrode (such as indium tin oxide (ITO)) and an opaque, refl ective metal electrode. These devices have shown high power conversion efficiencies (PCE) greater than 8%. [ 1 ] Semi-transparent organic photovoltaic cells (STOPVs), an extension of OPVs which utilize transparent conductive materials as both electodes, offer an extensive spectra of applications such as power-generating windows for buildings and automobiles, foldable solar curtains, and other aesthetic architectural uses. Furthermore, the capability of converting incident light to electric power shows the potential of STOPVs in the fi eld of effi cient energy conservation.When compared to vapor deposited small molecule STOPVs [ 2a ] or silicon-based STPVs, [ 2b ] the development of solution processed polymer-based STOPVs is lagging due to the absence of effi cient donor polymers and electrodes with proper transparency. STOPVs require more sophisticated materials and refi ned device engineering to simultaneously optimize both PCE and device transmittance, which are often contradictory to each other. In addition, for STOPVs to have practical solar window applications, good transparency perception (at least ≥ 20%) and color rendering properties are required under regular scene illumination. [ 2c ] To date, the state-of-the-art polymer-based STOPVs have either relatively low performance ( ≤ 3%) or unsatisfactory average visible transmittance (AVT) and color purity. [ 3 − 6 ] Therefore, there is a strong need to develop suitable polymer materials and novel device confi gurations to achieve improved PCE and transmittance for practical applications.In order for a device to have high PCE and transmittance in addition to proper color rendering index, it is critical to utilize appropriate thin BHJ layers that can effi ciently harvest the proper spectrum of light and electrodes with high transmittance and electrical conductivity. Until now, the frequently reported STOPVs still use a rather thick (at least 100 nm) poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC 61 BM) based BHJ layer. The dominant absorption of P3HT is located in the yellow-green wavelength region (500 ∼ 600 nm) where human eyes have the highest sensitivity, therefore leading to poor color perception and rendering properties. [ 3,4,7,8 ] The optimal materials for solar window applications should have ample light absorption outside of regions where human eyes are the most sensitive; at the same time allowing transmittance of visible light extensively. As a result, polymers with a band-gap smaller than P3HT have become a viable option for STOPVs. [ 4 ] Although these STOPVs showed improved transparency perce...

Thin Films for Advanced Glazing Applications

“…There are several organic-based approaches that produce semi-transparent OPV devices that exhibit good electrical performance (Figure 8), whereby they are composed of organic electronic materials, and transparent electrodes based on a wide range of different materials, including conducting polymers [122][123][124][125], thin metal films [126], sputtered transparent conducting oxides of LiCoO2/Al [127], carbon nanotubes [122], graphene [128], and silver nanowires (Ag NWs) [129][130][131][132][133]. Recently, a study by Beiley et al [134], has shown the development of a semi-transparent OPV which consists of a silver nanowire (Ag NW) and zinc oxide nanoparticle (ZnO NP) composite top electrode, and has a power conversion efficiency of 5.0%.…”

Semi-transparent polymer solar cells

“…First, we will consider what is, perhaps, the most straightforward approach consisting of further decreasing the polymer band gap to obtain a larger transparency in the visible spectrum. [79][80][81] One of the most relevant features of this approach is that it provides a very nice colorless high level of transparency. On the other hand, the limited harvesting at all wavelengths resulting from the low reflectivity of the top electrode can be partially compensated with the incorporation of an additional absorber layer in a tandem configuration.…”

Finely Tuned Polymer Interlayers Enhance Solar Cell Efficiency

“…[1,2] For example,i nterlayers located between the active layer and conductive electrodes improve the selectivity of charge transport, and minimize series resistance (R s ), leading to PCE values exceeding 9% for single junction PSCs. [3][4][5][6][7] A blend of poly(ethylenedioxythiophene)a nd poly(styrene sulfonate) (PEDOT:PSS) functions as as olution-processible hole-selective anode modification layer that has proven generally useful for PSCs.R ecent efforts have been devoted to developing new cathode modification layers to enhance electron extraction efficiency.S mall-molecule organic interlayers integrated into PSCs afford noteworthy device improvement, including functional fullerenes, [4,[8][9][10][11][12][13][14][15][16] perylene diimides, [17] and oligomeric fluorenes. [5] Polymer interlayers provide advantages of both facile solution processing and robust film formation, with two recently reported examples being poly(ethyleneimine) (PEI) [18,19] and tertiary-aminesubstituted polyfluorene (PFN).…”