Intermediate band solar cells: Present and future

Iñigo Ramiro,Antonio Martí

doi:10.1002/pip.3351

Abstract

AbstractIn the quest for high‐efficiency photovoltaics (PV), the intermediate band solar cell (IBSC) was proposed in 1997 as an alternative to tandem solar cells. The IBSC offers 63% efficiency under maximum solar concentration using a single semiconductor material. This high‐efficiency limit attracted the attention of the PV community, yielding to numerous intermediate band (IB) studies and IBSC prototypes employing a plethora of candidate IB materials. As a consequence, the principles of operation of the IBSC have been demonstrated, and the particularities and difficulties inherent to each different technological implementation of the IBSC have been reasonably identified and understood. From a theoretical and experimental point of view, the IBSC research has reached a mature stage. Yet we feel that, driven by the large number of explored materials and technologies so far, there is some confusion about what route the IBSC research should take to transition from the proof of concept to high efficiency. In this work, we give our view on which the next steps should be. For this, first, we briefly review the theoretical framework of the IBSC, the achieved experimental milestones, and the different technological approaches used, with special emphasis on those recently proposed.

Highlights

AND CONTEXTThe intermediate band solar cell (IBSC) was proposed by Luque and Martí[1] as a structurally simple yet highly efficient photovoltaic (PV) concept
Each technology has its strengths and weaknesses, but overall Quantum dots (QDs) is the one that has verified most of the phenomena expected in IBSC operation
Regarding deep-level impurities (DLIs) and Highly mismatched alloys (HMAs), we advise the community to focus efforts on understanding the mechanisms of non-radiative recombination introduced by the IB, so that they can be suppressed

Summary

INTRODUCTION

The intermediate band solar cell (IBSC) was proposed by Luque and Martí[1] as a structurally simple yet highly efficient photovoltaic (PV) concept. Thanks to the presence of the IB and the carrier selective contacts, IBSCs can achieve efficiencies as high as 63%1 under maximum light concentration (see Figure 1b), which represents a relative increment of around 50% with respect to conventional SGSCs.[3] the limiting efficiency of an IBSC is very close to that of a tandem cell with three gaps.[8] The potential high efficiency, combined with a conceptually simple structure, for instance, when compared with multi-junction solar cells (MJSC), were probably decisive factors that motivated extensive research on the topic.[9,10] Many different IB materials have been explored, as we will discuss later on. The SGSC delivers higher output voltage but a much lower current, consequence of the lower number of high-energy photons in the solar spectrum This example serves to clarify the concept of voltage preservation in IBSCs. Voltage is said to be preserved when it is not limited by the sub-gaps introduced by the IB, this is, when e·V > EH. The removal of the constraint of non-overlapping absorption coefficients results in different efficiency values and can be beneficial when the IB is not placed at the optimum position.[15,17,18]

TECHNOLOGICAL APPROACHES EMPLOYED IN IBSC

Achieved and pending experimental milestones

IBSC technology status

FUTURE DIRECTIONS

Findings

CONCLUSIONS