Abstract
After 60 years of research, silicon solar cell efficiency saturated close to the theoretical limit, and radically new approaches are needed to further improve the efficiency. The use of tandem systems raises this theoretical power conversion efficiency limit from 34% to 45%. We present the advantageous spectral stability of using voltage-matched tandem solar cells with respect to their traditional series-connected counterparts and experimentally demonstrate how singlet fission can be used to produce simple voltage-matched tandems. Our singlet fission silicon–pentacene tandem solar cell shows efficient photocurrent addition. This allows the tandem system to benefit from carrier multiplication and to produce an external quantum efficiency exceeding 100% at the main absorption peak of pentacene.
Highlights
C onventional single-junction solar cells are limited in efficiency to about 34%, mainly because of nonabsorbed below-band-gap photons and the loss of energy via thermalization of high-energy electron−hole pairs
We use a novel architecture, combining a conventional monocrystalline silicon solar cell with a pentacene cell connected electrically in parallel. In such a parallel tandem architecture, the efficiency of silicon photovoltaics can be enhanced with singlet fission by potentially doubling the current obtained from high-energy photons
The design and manufacturing of tandem solar cells is challenging and very costly,[10,11] and current matching cannot be maintained as the solar spectrum changes, under
Summary
The band gap combinations of all tandem cells were optimized for the AM1.5G standard spectrum. We measure the Letter pentacene tandem cell in a modified configuration where the singlet fission subcell features a reflective silver back-contact and is placed at a small off-normal angle from the incoming light In this configuration, light passes through the pentacene layer twice, before and after being reflected at the back-contact, and reaches the silicon solar cell (see inset of Figure 4B). This allows the doubling of the current from high-energy photons and reduction of the voltage to match the voltage of the low-band-gap subcell We have realized this parallel tandem solar cell using pentacene as the singlet fission sensitizer together with a monocrystalline silicon solar cell and demonstrated that the current of the two subcells adds.
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