Organic photovoltaics (OPV) is a next-generation solar cell technology based on organic semiconductors .
It can be used for scalable clean energy and wearable electronic devices.
However, the compounding of photogenerated carriers in OPVs leads to irreversible energy conversion losses, which prevents further improvements in the power conversion efficiency (PCE) of OPVs.
A recent study published in Nature Energy shows that researchers at the City University of Hong Kong have overcome this obstacle.
They developed a new device engineering strategy that successfully suppressed OPV energy conversion losses, achieving a record photovoltaic conversion efficiency of more than 19%.
In OPV, the energy from sunlight generates excitons (negatively charged electrons and positively charged holes bound together) and dissociates into free electrons and holes at the nanoscale donor-receptor interface to produce charge carriers, or photocurrents.
However, if these charge carriers are not collected by the electrodes, they meet again at the donor-receptor interface, recombine into low-energy triplet excitons T₁, and relax back to the ground state.
During this irreversible process, energy is lost in the form of heat and photocurrent is lost, greatly limiting the maximum PCE achievable by OPV.
Instead of the conventional highly mixed native heterojunction (BHJ), the researchers used a planar mixed heterojunction (PMHJ) with reduced mixing of donor and acceptor materials.
The reduction of the donor-receptor contact enables the maximum suppression of the charge transfer state-mediated loss pathway at the interface and the reduction of T₁ concentration.
This study fundamentally changes the past strategy of improving OPV performance by increasing the donor-receptor contact interface.
and it provides a comprehensive basis for the future commercialization of OPV technology.