Supplemental Tables and Figures For:

Transparent, Near-Infrared Organic Photovoltaic Solar Cells for Window and Energy-Scavenging Applications

Richard R. Lunt1,2a), Vladimir Bulovic1,b)

1Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA

2Department of Chemical Engineering and Materials Science, MSU, East Lansing, MI

Table SI. Performance of control OPVs with Ag cathode, transparent OPVs with ITO cathode, and OPVs with ITO cathode and NIR mirror, at 0.8 sun illumination corrected for solar spectrum mismatch. Short circuit current, JSC, open circuit voltage, VOC, fill factor, FF, power conversion efficiency, P, and the average visible transmission, AVT, are indicated.

Cathode Thickness
(nm) / Cathode
Composition / JSC
(mA/cm2) / VOC
(V) / FF
- / P
(%) / AVT(%)
100 / Ag / 4.7 / 0.77 / 0.55 / 2.4 / 0
20 / ITO / 1.5 / 0.69 / 0.39 / 0.5 / 67
120 / ITO / 3.2 / 0.71 / 0.46 / 1.3 / 65
20 / ITO/NIR mirror / 2.2 / 0.73 / 0.32 / 0.6 / 53
40 / ITO/NIR mirror / 2.5 / 0.71 / 0.49 / 1.1 / 55
80 / ITO/NIR mirror / 2.9 / 0.71 / 0.46 / 1.2 / 56
120 / ITO/NIR mirror / 4.4 / 0.71 / 0.44 / 1.7 / 56
170 / ITO/NIR mirror / 3.2 / 0.69 / 0.48 / 1.3 / 66

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Figure S1. (a) Measured solar simulator spectrum (left axis, black line) exhibiting characteristics of the Xe-lamp and NREL reported mc-Si external quantum efficiency (EQE) for the reference-diode used to measure the solar simulator intensity (right-axis, red line). Because the responsivity of the reference diode extends significantly beyond the response of the OPV cell, the extra NIR light from the solar simulator (compared to the AM1.5G spectrum) results in solar mismatch factors less than 1. (b) Measured (left axis, black circles) and calculated (left axis, blue line) reflectivity of the distributed Bragg reflector used in this study as the transparent, NIR mirror. Also shown is the transmission spectrum (right-axis red-line) of the broad-band antireflection (BBAR) coatings.

Figure S2. Transfer matrix simulations of the average visible transmission (AVT, left column) and short-circuit current (right column) of the transparent OPV architecture as a function of the anode and cathode ITO thicknesses without (top graphs), and with (bottom graphs), the NIR mirror. The dotted white line indicates the thickness of the ITO anode utilized in this study. The active layer structure was Anode/MoO3(20nm)/ClAlPc(15nm)/C60(30nm)/BCP(7.5nm)/Cathode where the exciton diffusion lengths of ClAlPc and C60 were estimated from fitting the magnitudes of the photocurrent and EQE of the control cell to be 8±4nm and 15±6nm, respectively.

Figure S3. Calculated optical field, |E|2, of the transparent OVP as a function of position at a fixed wavelength close to the peak absorption of the ClAlPc active layer (~740nm) for an ITO cathode thickness of 20nm (black line) and 120nm (red line). Note the enhancement of the field within the ClAlPc layer for the optimized ITO thickness, where the absorption is proportional to |E|2 integrated over position.

Figure S4. Picture of the full circuit assembly (left). Electrical connections are made to the ITO contacts of the OPV device via carbon-tape. The LCD clock is connected to circuitry (right) that limits the voltage and passes excess current to a small LED such that the clock works under a wide range of OPV illumination conditions. The LCD clock requires approximately 1.5V and 10mA and can be run by the solar cell for intensities ≥ 0.05 suns (note that under the ambient lighting < 0.01sun the clock is off).

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