Abstract
Polymer solar cells (PSCs) exhibit many advantages such as processing feasibility, capability of scaling up to large area, light weigh and flexibility. Thus we can fabricate cost-effective solar cells. However, mutual dissolution is one of the main problems for achieving PSCs with multilayer structure. In this work, we solve the problem by high temperature baking, spin-rinsing and buffer layer technique. The results show that this buffer layer technique with glycol would reduce the mutual dissolution problem and enhance the efficiency of multilayer structure devices. We use blending of P3HT and PCBM as active material in our study. Our main research is to modify the conventional bulk heterojunction (BHJ) structure with buffer layer technique. We spin an extra P3HT-rich layer (P layer) near the anode before a normal layer with 1:1 wt of P3HT/PCBM (I layer) being deposited and insert an extra P3HT-poor layer (N layer) near the cathode. The gradually-distributed active layer allow for efficient exciton separation and better carrier extraction at the same time. Therefore, this leads to a better PCE of PSCs. We successfully demonstrated bi-layer structure devices and multilayer p-i-n structure of P3HT-rich/blend/PCBM-rich in our study. The result shows that the dark current near operating voltage is suppressed. Besides, the recombination is significantly decreased. From the parameters extracted form the circuit model, an increased shunt resistance (Rsh) is observed. This increased Rsh lead to a higher operating voltage and thus an increased FF. The power conversion efficiency with P-I-N structured is enhanced from 2.46% to 3.35%! The buffer layer technique can be used as a new approach for fabrication of multilayer PSCs or tandem cells. Besides, the P-I-N structure is benefiting for lowering the leakage current and recombination current. This has potential of being applied in fabrication of large-area PSCs which usually have more leakage path and higher recombination current.