Laboratory of Organic Photonics and Iontronics

Laboratory of Organic Photonics and Iontronics
Laboratory of Organic Photonics and Iontronics

Polymer Solar Cells


Flexible, low-cost plastic photovoltaic solar cells are immensely appealing. Early Schottky barrier-type polymer solar cells, however, had very low power conversion efficiencies on the order of 0.1%.

In 1995, I co-invented the revolutionary polymer bulk heterojunction (BHeJ) solar cell (Science 270:1789, 1995). With over 8,000 citations, the seminal Science paper is the most important work in the field of polymer photovoltaics. 

The BHeJ cells are based on a mixture of a polymer host and a fullerene guest, which allows for a near 100% charge separation upon photoexcitation. I showed that the cell efficiency was increased with fullerene loading (Synthetic Metals 84:979, 1996). The power conversion efficiency of BHeJ solar cells has now reached over 10% under simulated sunlight in some leading labs in the field. 

Our group's recent research in this area focused on the elucidation of the open-circuit voltage (VOC) in polymer PV cells. I investigated polymer BHeJ PV cells in a planar configuration (JAP 104:084512, 2008). As expected, planar cells with identical electrodes did not exhibit any photovoltaic response due to symmetry. Cells with dissimilar electrodes, on the other hand, showed a significant open-circuit voltage. The planar PV cells allowed for site-selective illumination and did not suffer from the inherent asymmetry of a sandwich cell, which displayed an anomalous VOC even when the front and back electrodes were made of the same metal (JAP 106:044505, 2009).

Currently we are conducting optical-beam-induced-current (OBIC) imaging of extremely large planar BHeJ cells. The results should provide vital information about the origin of the PV response in a polymer BHeJ solar cell and guide the design of more efficient devices.

optical-beam-induced-current (OBIC) imaging of extremely large planar BHeJ cells